2022/12/02 更新

写真a

フジタ トモヒロ
藤田 智弘
Scopus 論文情報  
論文数: 0  Citation: 0  h-index: 22

Citation Countは当該年に発表した論文の被引用数

所属
附属機関・学校 高等研究所
職名
講師(任期付)
メールアドレス
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他学部・他研究科等兼任情報

  • 理工学術院   先進理工学部

 

論文

  • Can primordial parity violation explain the observed cosmic birefringence?

    Tomohiro Fujita, Yuto Minami, Maresuke Shiraishi, Shuichiro Yokoyama

       2022年08月

     概要を見る

    Recently, the cross-correlation between $E$- and $B$-mode polarization of the
    cosmic microwave background (CMB), which is well explained by cosmic
    birefringence with rotation angle $\beta\approx 0.3$ deg, has been found in CMB
    polarization data. We carefully investigate the possibility of explaining the
    observed $EB$ correlation by the primordial chiral gravitational waves (CGWs),
    which can be generated in the parity-violating theories in the primordial
    Universe. We found that the CGWs scenario does not work due to the
    overproduction of the $BB$ auto-correlation which far exceeds the observed one
    by SPTPol and POLARBEAR.

  • Stochastic formalism for U(1) gauge fields in axion inflation

    Tomohiro Fujita, Kyohei Mukaida, Yuichiro Tada

       2022年06月

     概要を見る

    We develop the stochastic formalism for $\mathrm{U}(1)$ gauge fields that has
    the Chern-Simons coupling to a rolling pseudo-scalar field during inflation.
    The Langevin equations for the physical electromagnetic fields are derived and
    the analytic solutions are studied. Using numerical simulation we demonstrate
    that the electromagnetic fields averaged over the Hubble scale continuously
    change their direction and their amplitudes fluctuate around the analytically
    obtained expectation values. Though the isotropy is spontaneously broken by
    picking up a particular local Hubble patch, each Hubble patch is understood
    independent and the isotropy is conserved globally by averaging all the Hubble
    patches.

  • Perturbation theory of LSS in the $Λ$CDM Universe: exact time evolution and the two-loop power spectrum

    Matteo Fasiello, Tomohiro Fujita, Zvonimir Vlah

       2022年05月

     概要を見る

    We derive exact analytic solutions for density and velocity fields to all
    orders in Eulerian perturbation theory for $\Lambda$CDM cosmology. In
    particular, we show that density and velocity field kernels can be written in a
    separable form in time and momenta at each perturbative order. The kernel
    solutions are built from an analytic basis of momentum operators and their
    time-dependent coefficients, which solve a set of recursive differential
    equations. We also provide an exact closed perturbative solution for such
    coefficients, expanding around the (quasi-)EdS approximation. We find that the
    perturbative solution rapidly converges towards the numerically obtained
    solutions and its leading order result suffices for any practical requirements.
    To illustrate our findings, we compute the exact two-loop dark matter density
    and velocity power spectra in $\Lambda$CDM cosmology. We show that the
    difference between the exact $\Lambda$CDM and the (quasi-)EdS approximated
    result can reach the level of several percent. This deviation can be partially
    mitigated by exploiting the degeneracy with the EFT counterterms. As an
    additional benefit of our algorithm for the solutions of time-dependent
    coefficients, the computational complexity of power spectra loops in
    $\Lambda$CDM is reduced to the same level of the EdS case. In performing the
    two-loop computation, we devise an explicit method to implement the so-called
    IR cancellations, as well as the cancellations arising as a consequence of mass
    and momentum conservation.

  • Stochastic effects on observation of ultralight bosonic dark matter

    Hiromasa Nakatsuka, Soichiro Morisaki, Tomohiro Fujita, Jun'ya Kume, Yuta Michimura, Koji Nagano, Ippei Obata

       2022年05月

     概要を見る

    Ultralight bosonic particles are fascinating candidates of dark matter (DM).
    It behaves as classical waves in our Galaxy due to its large number density.
    There have been various methods proposed to search for the wave-like DM, such
    as methods utilizing interferometric gravitational-wave detectors.
    Understanding the characteristics of DM signals is crucial to extract the
    properties of DM from data. While the DM signal is nearly monochromatic with
    the angular frequency of its mass, the amplitude and phase are gradually
    changing due to the velocity dispersion of DMs in our Galaxy halo. The
    stochastic amplitude and phase should be properly taken into account to
    accurately constrain the coupling constant of DM from data. Previous works
    formulated a method to obtain the upper bound on the coupling constant
    incorporating the stochastic effects. One of these works compared the upper
    bound with and without the stochastic effect in a measurement time that is much
    shorter than the variation time scale of the amplitude and phase. In this
    paper, we extend their formulation to arbitrary measurement time and evaluate
    the stochastic effects. Moreover, we investigate the velocity-dependent signal
    for dark photon DM including an uncertainly of the velocity. We demonstrate
    that our method accurately estimates the upper bound on the coupling constant
    with numerical simulations. We also estimate the expected upper bound of the
    coupling constant of axion DM and dark photon DM from future experiments in a
    semi-analytic way. The stochasticity especially affects constraints on a small
    mass region. Our formulation offers a generic treatment of the ultralight
    bosonic DM signal with the stochastic effect.

  • Effective treatment of U(1) gauge field and charged particles in axion inflation

    Tomohiro Fujita, Jun'ya Kume, Kyohei Mukaida, Yuichiro Tada

       2022年04月

     概要を見る

    The axionic inflaton with the Chern-Simons coupling may generate U(1) gauge
    fields and charged particles simultaneously. In order to incorporate the
    backreaction from the charged particles on the gauge fields, we develop a
    procedure to obtain an equilibrium solution for the gauge fields by treating
    the induced current as effective electric and magnetic conductivities.
    Introducing mean field approximation, and numerically solving self-consistency
    equations, we find that the gauge field amplitudes are drastically suppressed.
    Interestingly, as the production becomes more efficient, the charged particles
    gain a larger part of the transferred energy from the inflaton and eventually
    dominate it. Our formalism offers a basis to connect this class of inflationary
    models to a rich phenomenology such as baryogenesis and magnetogenesis.

  • Gravitational waves detectable in laser interferometers from axion-SU(2) inflation

    Tomohiro Fujita, Kaname Imagawa, Kai Murai

       2022年03月

     概要を見る

    Chromo-natural inflation (CNI) is an inflationary model where an axion
    coupled with SU$(2)$ gauge fields acts as the inflaton. In CNI, the gauge
    fields have nonzero vacuum expectation values (VEVs), which results in the
    enhancement of gravitational waves (GWs). The original CNI is ruled out by the
    Planck observations due to the overproduction of GWs. In this work, we consider
    an inflationary model where the gauge fields acquire nonzero VEVs after the CMB
    modes exit the horizon. Moreover, we add to the model another field that
    dominates the universe and drives inflation after the axion starts to oscillate
    and the gauge field VEVs vanish. By performing numerical simulations, we find a
    parameter space where the enhanced GWs do not violate the CMB constraints and
    can be detected by the future GWs observations such as BBO and ET.

    DOI

    Scopus

  • Universality of linear perturbations in SU($N$)-natural inflation

    Tomohiro Fujita, Kai Murai, Ryo Namba

       2022年03月

     概要を見る

    We prove the universality of predictions for linear perturbations from the
    entire class of models of inflation driven by a pseudo-scalar field coupled to
    an SU($N$) gauge boson, where SU($2$) subgroups in the SU($N$) crossed with the
    background spatial SO($3$) spontaneously break into a single SO($3$). The
    effect of which SU($2$) subgroup in SU($N$) acquires a VEV through spontaneous
    symmetry breaking can be quantified by a single parameter $\lambda$, which
    always appears in combination with the gauge coupling constant $g$. In the
    linear perturbations, as well as the background system, the same dynamics and
    predictions as in the chromo-natural inflation hold for its SU($N$) extension
    by replacing $g \to g\lambda$. The latter models thereby draw the same
    prediction curve on the $n_s$-$r$ plane as the former at the tree level as long
    as $g \lambda$ stays constant during inflation. We briefly discuss possible
    transitions from one value of $\lambda$ to another during inflation and the
    observational prospects.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • When does the Schwinger preheating occur?

    So Okano, Tomohiro Fujita

    Journal of Cosmology and Astroparticle Physics   2022 ( 03 ) 040 - 040  2022年03月

     概要を見る

    Abstract

    When the inflaton couples to photons and amplifies electric fields, charged particles produced via the Schwinger effect can dominate the universe after inflation, which is dubbed as the Schwinger preheating. Using the hydrodynamic approach for the Boltzmann equation, we numerically study two cases, the Starobinsky inflation model with the kinetic coupling and the Watanabe-Kanno-Soda inflation model. The Schwinger preheating is not observed in the latter model but occurs for a sufficiently large inflaton-photon coupling in the first model. We analytically address its condition and derive a general attractor solution of the electric fields. The occurrence of the Schwinger preheating in the first model is determined by whether the electric fields enter the attractor solution during inflation or not.

    DOI

    Scopus

  • Inflation with two-form field: the production of primordial black holes and gravitational waves

    Tomohiro Fujita, Hiromasa Nakatsuka, Ippei Obata, Sam Young

       2022年02月

     概要を見る

    Antisymmetric tensor field (two-form field) is a ubiquitous component in
    string theory and generally couples to the scalar sector through its kinetic
    term. In this paper, we propose a cosmological scenario that the particle
    production of two-form field, which is triggered by the background motion of
    the coupled inflaton field, occurs at the intermediate stage of inflation and
    generates the sizable amount of primordial black holes as dark matter after
    inflation. We also compute the secondary gravitational waves sourced by the
    curvature perturbation and show that the resultant power spectra are testable
    with the future space-based laser interferometers.

  • Gravitational wave trispectrum in the axion-SU(2) model

    Tomohiro Fujita, Kai Murai, Ippei Obata, Maresuke Shiraishi

    Journal of Cosmology and Astroparticle Physics   2022 ( 01 ) 007 - 007  2022年01月

     概要を見る

    <jats:title>Abstract</jats:title>
    <jats:p>We study the trispectrum of the gravitational waves (GWs) generated through the dynamics of an axionic spectator field and SU(2) gauge fields during inflation.
    In non-Abelian gauge theory, the gauge fields have four-point self-interactions, which induce the tree-level GW trispectrum.
    We formulate this type of the GW trispectrum including the non-dynamical contributions and evaluate it in the equilateral limit as a unique signal of this model.
    We find that the ratio of the GW trispectrum to the cube of the scalar power spectrum can be as large as 𝒪(10<jats:sup>6</jats:sup>) in the viable parameter space, which could be captured in the CMB observations.</jats:p>

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Ultralight dark matter searches with KAGRA gravitational wave telescope

    Yuta Michimura, Tomohiro Fujita, Jun’ya Kume, Soichiro Morisaki, Koji Nagano, Hiromasa Nakatsuka, Atsushi Nishizawa, Ippei Obata

    Journal of Physics: Conference Series   2156 ( 1 ) 012071 - 012071  2021年12月

     概要を見る

    Abstract

    Among various dark matter candidates, bosonic ultralight fields with masses below 1eV are well motivated. Recently, a number of novel approaches have been put forward to search for ultralight dark matter candidates using laser interferometers at various scales. Those include our proposals to search for axion-like particles (ALPs) and vector fields with laser interferometric gravitational wave detectors. ALPs can be searched for by measuring the oscillating polarization rotation of laser light. Massive vector fields weakly coupled to the standard model sector can also be searched for by measuring the oscillating forces acting on the suspended mirrors of the interferometers. In this paper, the current status of the activities to search for such ultralight dark matter candidates using a gravitational wave detector in Japan, KAGRA, is reviewed. The analysis of data from KAGRA’s observing run in 2020 to search for vector dark matter, and the installation of polarization optics to the arm cavity transmission ports of the interferometer to search for ALPs in future observing runs are underway.

    DOI

    Scopus

  • Dark matter Axion search with riNg Cavity Experiment DANCE: Design and development of auxiliary cavity for simultaneous resonance of linear polarizations

    Hiroki Fujimoto, Yuka Oshima, Masaki Ando, Tomohiro Fujita, Yuta Michimura, Koji Nagano, Ippei Obata

       2021年10月

     概要を見る

    Axion-like particles (ALPs) are undiscovered pseudo-scalar particles that are
    candidates for ultralight dark matter. ALPs interact with photons slightly and
    cause the rotational oscillation of linearly polarized light. Dark matter Axion
    search with riNg Cavity Experiment (DANCE) searches for ALP dark matter by
    amplifying the rotational oscillation with a bow-tie ring cavity. Simultaneous
    resonance of linear polarizations is necessary to amplify both the carrier
    field and the ALP signal, and to achieve the design sensitivity. The
    sensitivity of the current prototype experiment DANCE Act-1 is less than
    expectation by around three orders of magnitude due to the resonant frequency
    difference between s- and p-polarization in the bow-tie ring cavity. In order
    to tune the resonant frequency difference, the method of introducing an
    auxiliary cavity was proposed. We designed an auxiliary cavity that can cancel
    out the resonant frequency difference and realize simultaneous resonance,
    considering optical loss. We also confirmed that the sensitivity of DANCE Act-1
    with the auxiliary cavity can reach the original sensitivity.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • SU($N$)-natural inflation

    Tomohiro Fujita, Kyohei Mukaida, Kai Murai, Hiromasa Nakatsuka

       2021年10月

     概要を見る

    We study SU($N$) gauge fields that couple to the inflaton through the
    Chern-Simons term. We provide a general procedure to construct homogeneous,
    isotropic, and attractor solutions of the gauge fields during inflation. The
    gauge fields develop various VEVs corresponding to different spontaneous
    symmetry breaking patterns of SU($N$) where embedded SU($2$) subgroups are
    broken with the spatial rotation SO($3$) symmetry. As specific examples, we
    construct the stable solutions for $N = 3$ and $4$. We also numerically solve
    the gauge field dynamics and confirm that our analytic solutions are complete
    and attractor. It is straightforward to apply our procedure to the other simple
    Lie groups.

    DOI

    Scopus

  • Axion dark matter search using arm cavity transmitted beams of gravitational wave detectors

    Koji Nagano, Hiromasa Nakatsuka, Soichiro Morisaki, Tomohiro Fujita, Yuta Michimura, Ippei Obata

    Physical Review D   104 ( 6 )  2021年09月

     概要を見る

    Axion is a promising candidate for ultralight dark matter which may cause a
    polarization rotation of laser light. Recently, a new idea of probing the axion
    dark matter by optical linear cavities used in the arms of gravitational wave
    detectors has been proposed [Phys. Rev. Lett. 123, 111301 (2019)]. In this
    article, a realistic scheme of the axion dark matter search with the arm cavity
    transmission ports is revisited. Since photons detected by the transmission
    ports travel in the cavity for odd-number of times, the effect of axion dark
    matter on their phases is not cancelled out and the sensitivity at low-mass
    range is significantly improved compared to the search using reflection ports.
    We also take into account the stochastic nature of the axion field and the
    availability of the two detection ports in the gravitational wave detectors.
    The sensitivity to the axion-photon coupling, $g_{a\gamma}$, of the
    ground-based gravitational wave detector, such as Advanced LIGO, with 1-year
    observation is estimated to be $g_{a\gamma} \sim 3\times10^{-12}$ GeV$^{-1}$
    below the axion mass of $10^{-15}$ eV, which improves upon the limit achieved
    by the CERN Axion Solar Telescope.

    DOI

  • Dark matter Axion search with riNg Cavity Experiment DANCE: Development of control system for long-term measurement

    Hiroki Fujimoto, Yuka Oshima, Masaki Ando, Tomohiro Fujita, Yuta Michimura, Koji Nagano, Ippei Obata

       2021年05月

     概要を見る

    Axion-like particles (ALPs) are pseudo-scalar particles that are candidates
    for ultralight dark matter. ALPs interact with photons slightly and cause the
    rotational oscillation of linear polarization. DANCE searches for ALP dark
    matter by enhancing the rotational oscillation in a bow-tie ring cavity. The
    signal to noise ratio of DANCE can be improved by long-term observation, and we
    are planning a year-long observation for the final DANCE. In this document, I
    will report on the control systems of the ring cavity we developed for the
    future long-term observation.

  • Resonant gravitational waves in dynamical Chern–Simons–axion gravity

    Tomohiro Fujita, Ippei Obata, Takahiro Tanaka, Kei Yamada

    Classical and Quantum Gravity   38 ( 4 ) 045010 - 045010  2021年02月  [査読有り]

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Chiral Gravitational Waves Produced in a Helical Magnetogenesis Model

    So Okano, Tomohiro Fujita

       2020年05月

     概要を見る

    We investigate the gravitational wave production induced by the primordial
    magnetic fields in a parity-violating magnetogenesis model. It is shown that
    the gravitational waves detectable by LISA, DECIGO or BBO and the magnetic
    fields strong enough to explain the blazar observation can be simultaneously
    produced. The magnetic fields and the gravitational waves have the same
    chirality and their amplitudes are related, which may also be tested by future
    observations.

    DOI

    Scopus

    11
    被引用数
    (Scopus)
  • DANCE: Dark matter Axion search with riNg Cavity Experiment

    Yuta Michimura, Yuka Oshima, Taihei Watanabe, Takuya Kawasaki, Hiroki Takeda, Masaki Ando, Koji Nagano, Ippei Obata, Tomohiro Fujita

    16TH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS (TAUP 2019)   1468  2020年  [査読有り]

     概要を見る

    We have proposed a new approach to search for axion dark matter with an optical ring cavity [Phys. Rev. Lett. 121, 161301 (2018)]. The coupling of photons to axions or axion-like particles makes a modulated difference in the phase velocity between left- and right-handed photons. Our method is to measure this phase velocity difference with a ring cavity, by measuring the resonant frequency difference between two circular polarizations. Our estimation shows that the sensitivity to axion-photon coupling constant g(a gamma) for axion mass m less than or similar to 10(-10) eV can be improved by several orders of magnitude compared with the current best limits. In this paper, we present the principles of the Dark matter Axion search with riNg Cavity Experiment (DANCE) and the status of the prototype experiment, DANCE Act-1.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Primordial tensor non-gaussianity from massive gravity

    Fujita, T., Mizuno, S., Mukohyama, S.

    Journal of Cosmology and Astroparticle Physics   2020 ( 1 )  2020年

    DOI

    Scopus

    6
    被引用数
    (Scopus)
  • Generation of chiral asymmetry via helical magnetic fields

    Schober, J., Fujita, T., Durrer, R.

    Physical Review D   101 ( 10 )  2020年

    DOI

    Scopus

    10
    被引用数
    (Scopus)
  • Scale-invariant helical magnetic fields from inflation

    Fujita, T., Durrer, R.

    Journal of Cosmology and Astroparticle Physics   2019 ( 9 )  2019年

    DOI

    Scopus

    25
    被引用数
    (Scopus)
  • Hunting Axion Dark Matter with Protoplanetary Disk Polarimetry

    Fujita, T., Tazaki, R., Toma, K.

    Physical Review Letters   122 ( 19 )  2019年

    DOI

    Scopus

    31
    被引用数
    (Scopus)
  • Tensor spectra templates for axion-gauge fields dynamics during inflation

    Fujita, T., Sfakianakis, E.I., Shiraishi, M.

    Journal of Cosmology and Astroparticle Physics   2019 ( 5 )  2019年

     概要を見る

    SU(2) gauge fields can generate large gravitational waves during inflation, if they are coupled to an axion which can be either the inflaton or a spectator field. The shape of the produced tensor power spectrum h depends on the form of the axion potential. We derive analytic expressions and provide general templates for h for various types of the spectator axion potential. Furthermore, we explore the detectability of the oscillatory feature, which is present in h in the case of an axion monodromy model, by possible future CMB B-mode polarization observations.

    DOI

    Scopus

    10
    被引用数
    (Scopus)
  • Axion dark matter search with interferometric gravitational wave detectors

    Nagano, K., Fujita, T., Michimura, Y., Obata, I.

    Physical Review Letters   123 ( 11 )  2019年

    DOI

    Scopus

    39
    被引用数
    (Scopus)
  • Mixed non-gaussianity from axion-gauge field dynamics

    Fujita, T., Namba, R., Obata, I.

    Journal of Cosmology and Astroparticle Physics   2019 ( 4 )  2019年

    DOI

    Scopus

    14
    被引用数
    (Scopus)
  • Hunting for statistical anisotropy in tensor modes with B -mode observations

    Hiramatsu, T., Yokoyama, S., Fujita, T., Obata, I.

    Physical Review D   98 ( 8 )  2018年

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Erratum: Critical constraint on inflationary magnetogenesis (Journal of Cosmology and Astroparticle Physics (2014) (013))

    Fujita, T., Yokoyama, S.

    Journal of Cosmology and Astroparticle Physics   2014 ( 5 )  2014年

    DOI

    Scopus

    9
    被引用数
    (Scopus)

▼全件表示

Misc

  • Blue-tilted Primordial Gravitational Waves from Massive Gravity

    Tomohiro Fujita, Sachiko Kuroyanagi, Shuntaro Mizuno, Shinji Mukohyama

    Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics   789  2018年08月

     概要を見る

    We study a theory of massive tensor gravitons which predicts blue-tilted and
    largely amplified primordial gravitational waves. After inflation, while their
    mass is significant until it diminishes to a small value, gravitons are diluted
    as non-relativistic matter and hence their amplitude can be substantially
    amplified compared to the massless gravitons which decay as radiation. We show
    that such gravitational waves can be detected by interferometer experiments,
    even if their signal is not observed on the CMB scales.

    DOI

  • Footprint of Two-Form Field: Statistical Anisotropy in Primordial Gravitational Waves

    Ippei Obata, Tomohiro Fujita

    Physical Review D   99 ( 2 )  2018年07月

     概要を見る

    We study the observational signatures of two-form field in the inflationary
    cosmology. In our setup a two-form field is kinetically coupled to a spectator
    scalar field and generates sizable gravitational waves and smaller curvature
    perturbation. We find that the sourced gravitational waves have a distinct
    signature: they are always statistically anisotropic and their spherical
    moments are non-zero for hexadecapole and tetrahexacontapole, while the
    quadrupole moment vanishes. Since their amplitude can reach
    $\mathcal{O}(10^{-3})$ in the tensor-to-scalar ratio, we expect this novel
    prediction will be tested in the next generation of the CMB experiments.

    DOI

  • Optical Ring Cavity Search for Axion Dark Matter

    Ippei Obata, Tomohiro Fujita, Yuta Michimura

    Physical Review Letters   121 ( 16 )  2018年05月

     概要を見る

    We propose a novel experiment to search for axion dark matter which
    differentiates the phase velocities of the left and right-handed polarized
    photons. Our optical cavity measures the difference of the resonant frequencies
    between two circular-polarizations of the laser beam. The design of our cavity
    adopts double-pass configuration to realize a null experiment and give a high
    common mode rejection of environmental disturbances. We estimate the potential
    sensitivity to the axion-photon coupling constant $g_{a\gamma}$ for the axion
    mass $m \lesssim 10^{-10}$ eV. In a low mass range $m \lesssim 10^{-15}$ eV, we
    can achieve $g_{a\gamma} \lesssim 3\times 10^{-16} ~\text{GeV}^{-1}$ which is
    beyond the current bound by several orders of magnitude.

    DOI

  • Quantum Entanglement in Multi-field Inflation

    Nadia Bolis, Tomohiro Fujita, Shuntaro Mizuno, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   2018 ( 9 )  2018年05月

     概要を見る

    We study the emergence of quantum entanglement in multi-field inflation. In
    this scenario, the perturbations of one field contribute to the observable
    curvature perturbation, while multi-field dynamics with the other fields affect
    the curvature perturbation through particle production and entanglement. We
    develop a general formalism which defines the quantum entanglement between the
    perturbations of the multiple fields both in the Heisenberg and Schr\"odinger
    pictures, and show that entanglement between different fields can arise
    dynamically in the context of multi-field inflationary scenarios. We also
    present a simple model in which a sudden change in the kinetic matrix of the
    scalar fields generates entanglement and an oscillatory feature appears in the
    power spectrum of the inflaton perturbation.

    DOI

  • Tensor Non-Gaussianity from Axion-Gauge-Fields Dynamics : Parameter Search

    Aniket Agrawal, Tomohiro Fujita, Eiichiro Komatsu

    Journal of Cosmology and Astroparticle Physics   2018 ( 6 )  2018年02月

     概要を見る

    We calculate the bispectrum of scale-invariant tensor modes sourced by
    spectator SU(2) gauge fields during inflation in a model containing a scalar
    inflaton, a pseudoscalar axion and SU(2) gauge fields. A large bispectrum is
    generated in this model at tree-level as the gauge fields contain a tensor
    degree of freedom, and its production is dominated by self-coupling of the
    gauge fields. This is a unique feature of non-Abelian gauge theory. The shape
    of the tensor bispectrum is approximately an equilateral shape for $3\lesssim
    m_Q\lesssim 4$, where $m_Q$ is an effective dimensionless mass of the SU(2)
    field normalised by the Hubble expansion rate during inflation. The amplitude
    of non-Gaussianity of the tensor modes, characterised by the ratio $B_h/P^2_h$,
    is inversely proportional to the energy density fraction of the gauge field.
    This ratio can be much greater than unity, whereas the ratio from the vacuum
    fluctuation of the metric is of order unity. The bispectrum is effective at
    constraining large $m_Q$ regions of the parameter space, whereas the power
    spectrum constrains small $m_Q$ regions.

    DOI

  • Statistically Anisotropic Tensor Modes from Inflation

    Tomohiro Fujita, Ippei Obata, Takahiro Tanaka, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2018 ( 7 )  2018年01月

     概要を見る

    We consider the inflationary universe with a spectator scalar field coupled
    to a $U(1)$ gauge field and calculate curvature perturbation and gravitational
    waves (GWs). We find that the sourced GWs can be larger than the one from
    vacuum fluctuation and they are statistically anisotropic as well as linearly
    polarized. The GW power spectrum acquires higher multipole moments as
    $\mathcal{P}_h \propto (1-\cos^2\theta+\cos^4\theta-\cos^6\theta)$ irrespective
    of the model parameters.

    DOI

  • Does Anisotropic "Inflation" Produce a Small Statistical Anisotropy?

    Tomohiro Fujita, Ippei Obata

    Journal of Cosmology and Astroparticle Physics   2018 ( 1 )  2017年11月

     概要を見る

    Anisotropic inflation is an interesting model with an U(1) gauge field and it
    predicts the statistical anisotropy of the curvature perturbation characterized
    by a parameter $g_*$. However, we find that the background gauge field does not
    follow the classical attractor solution due to the stochastic effect. We
    develop the stochastic formalism of a vector field and solve Langevin and
    Fokker-Planck equations. It is shown that this model is excluded by the CMB
    constraint $g_*\le 10^{-2}$ with a high probability about $99.999\%$.

    DOI

  • Finding the chiral gravitational wave background of an axion-SU(2) inflationary model using CMB observations and laser interferometers

    Ben Thorne, Tomohiro Fujita, Masashi Hazumi, Nobuhiko Katayama, Eiichiro Komatsu, Maresuke Shiraishi

    Physical Review D   97 ( 4 )  2017年07月

     概要を見る

    A detection of B-mode polarization of the Cosmic Microwave Background (CMB)
    anisotropies would confirm the presence of a primordial gravitational wave
    background (GWB). In the inflation paradigm this would be an unprecedented
    probe of the energy scale of inflation as it is directly proportional to the
    power spectrum of the GWB. However, similar tensor perturbations can be
    produced by the matter fields present during inflation, breaking this simple
    relationship. It is therefore important to be able to distinguish between
    different generation mechanisms of the GWB. In this paper, we analyse the
    detectability of a new axion-SU(2) gauge field model using its chiral,
    scale-dependent tensor spectrum. We forecast the detectability of the resulting
    CMB TB and EB cross-correlations by the LiteBIRD satellite, considering the
    effects of residual foregrounds, gravitational lensing, and for the first time
    assess the ability of such an experiment to jointly detect primordial TB and EB
    spectra and self-calibrate its polarimeter. We find that LiteBIRD will be able
    to detect the chiral signal for $r_*>0.03$ with $r_*$ denoting the
    tensor-to-scalar ratio at the peak scale, and that the maximum signal-to-noise
    for $r_*<0.07$ is $\sim 2$. We go on to consider an advanced stage of a
    LISA-like mission, and find that such experiments would complement CMB
    observations by providing sensitivity to GWB chirality on scales inaccessible
    to the CMB. We conclude that in order to use the CMB to distinguish this model
    from a conventional vacuum fluctuation model two-point statistics provide some
    power, but to achieve high statistical significance we would require higher
    order statistics which take advantage of the model's non-Gaussianity. On the
    other hand, in the case of a spectrum peaked at very small scales, inaccessible
    to the CMB, a highly significant detection could be made using space-based
    laser interferometers.

    DOI

  • Large Tensor Non-Gaussianity from Axion-Gauge Fields Dynamics

    Aniket Agrawal, Tomohiro Fujita, Eiichiro Komatsu

    Physical Review D   97 ( 10 )  2017年07月

     概要を見る

    We show that an inflation model in which a spectator axion field is coupled
    to an SU(2) gauge field produces a large three-point function (bispectrum) of
    primordial gravitational waves, $B_{h}$, on the scales relevant to the cosmic
    microwave background experiments. The amplitude of the bispectrum at the
    equilateral configuration is characterized by
    $B_{h}/P_h^2=\mathcal{O}(10)\times \Omega_A^{-1}$, where $\Omega_A$ is a
    fraction of the energy density in the gauge field and $P_h$ is the power
    spectrum of gravitational waves produced by the gauge field.

    DOI

  • Does the detection of primordial gravitational waves exclude low energy inflation?

    Tomohiro Fujita, Ryo Namba, Yuichiro Tada

    Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics   778  2017年05月

     概要を見る

    We show that a detectable tensor-to-scalar ratio $(r\ge 10^{-3})$ on the CMB
    scale can be generated even during extremely low energy inflation which
    saturates the BBN bound $\rho_{\rm inf}\approx (30 {\rm MeV})^4$. The source of
    the gravitational waves is not quantum fluctuations of graviton but those of
    $SU(2)$ gauge fields, energetically supported by coupled axion fields. The
    curvature perturbation, the backreaction effect and the validity of
    perturbative treatment are carefully checked. Our result indicates that
    measuring $r$ alone does not immediately fix the inflationary energy scale.

    DOI

  • Very Massive Tracers and Higher Derivative Biases

    Tomohiro Fujita, Valentin Mauerhofer, Leonardo Senatore, Zvonimir Vlah, Raul Angulo

    Journal of Cosmology and Astroparticle Physics   2020 ( 1 )  2016年09月

     概要を見る

    Most of the upcoming cosmological information will come from analyzing the
    clustering of the Large Scale Structures (LSS) of the universe through LSS or
    CMB observations. It is therefore essential to be able to understand their
    behavior with exquisite precision. The Effective Field Theory of Large Scale
    Structures (EFTofLSS) provides a consistent framework to make predictions for
    LSS observables in the mildly non-linear regime. In this paper we focus on
    biased tracers. We argue that in calculations at a given order in the dark
    matter perturbations, highly biased tracers will underperform because of their
    larger higher derivative biases. A natural prediction of the EFTofLSS is
    therefore that by simply adding higher derivative biases, all tracers should
    perform comparably well. We implement this prediction for the halo-halo and the
    halo-matter power spectra at one loop, and the halo-halo-halo,
    halo-halo-matter, and halo-matter-matter bispectra at tree-level, and compare
    with simulations. We find good agreement with the prediction: for all tracers,
    we are able to match the bispectra up to $k\simeq0.17\,h/$Mpc at $z=0$ and the
    power spectra to a higher wavenumber.

    DOI

  • Primordial Gravitational Waves from Axion-Gauge Fields Dynamics

    Emanuela Dimastrogiovanni, Matteo Fasiello, Tomohiro Fujita

    Journal of Cosmology and Astroparticle Physics   2017 ( 1 )  2016年08月

     概要を見る

    Inspired by the chromo-natural inflation model of Adshead&Wyman, we reshape
    its scalar content to relax the tension with current observational bounds.
    Besides an inflaton, the setup includes a spectator sector in which an axion
    and SU(2) gauge fields are coupled via a Chern-Simons-type term. The result is
    a viable theory endowed with an alternative production mechanism for
    gravitational waves during inflation. The gravitational wave signal sourced by
    the spectator fields can be much larger than the contribution from standard
    vacuum fluctuations, it is distinguishable from the latter on the basis of its
    chirality and, depending on the theory parameters values, also its tilt. This
    production process breaks the well-known relation between the tensor-to-scalar
    ratio and the energy scale of inflation. As a result, even if the Hubble rate
    is itself too small for the vacuum to generate a tensor amplitude detectable by
    upcoming experiments, this model still supports observable gravitational waves.

    DOI

  • Hubble induced mass after inflation in spectator field models

    Tomohiro Fujita, Keisuke Harigaya

    Journal of Cosmology and Astroparticle Physics   2016 ( 12 )  2016年07月

     概要を見る

    Spectator field models such as the curvaton scenario and the modulated
    reheating are attractive scenarios for the generation of the cosmic curvature
    perturbation, as the constraints on inflation models are relaxed. In this
    paper, we discuss the effect of Hubble induced masses on the dynamics of
    spectator fields after inflation. We pay particular attention to the Hubble
    induced mass by the kinetic energy of an oscillating inflaton, which is
    generically unsuppressed but often overlooked. In the curvaton scenario, the
    Hubble induced mass relaxes the constraint on the property of the inflaton and
    the curvaton, such as the reheating temperature and the inflation scale. We
    comment on the implication of our discussion for baryogenesis in the curvaton
    scenario. In the modulated reheating, the predictions of models e.g. the
    non-gaussianity can be considerably altered. Furthermore, we propose a new
    model of the modulated reheating utilizing the Hubble induced mass which
    realizes a wide range of the local non-gaussianity parameter.

    DOI

  • Fermionic Schwinger effect and induced current in de Sitter space

    Takahiro Hayashinaka, Tomohiro Fujita, Jun'ichi Yokoyama

    Journal of Cosmology and Astroparticle Physics   2016 ( 7 )  2016年03月

     概要を見る

    We explore Schwinger effect of spin 1/2 charged particles with static
    electric field in 1+3 dimensional de Sitter spacetime. We analytically
    calculate the vacuum expectation value of the spinor current which is induced
    by the produced particles in the electric field. The renormalization is
    performed with the adiabatic subtraction scheme. We find that the current
    becomes negative, namely it flows in the direction opposite to the electric
    field, if the electric field is weaker than a certain threshold value depending
    on the fermion mass, which is also known to happen in the case of scalar
    charged particles in 1+3 de Sitter spacetime. Contrary to the scalar case,
    however, the IR hyperconductivity is absent in the spinor case.

    DOI

  • Pre-reheating Magnetogenesis in the Kinetic Coupling Model

    Tomohiro Fujita, Ryo Namba

    Physical Review D   94 ( 4 )  2016年02月

     概要を見る

    Recent blazar observations provide growing evidence for the presence of
    magnetic fields in the extragalactic regions. While a natural speculation is to
    associate the production to inflationary physics, it has been known that
    magnetogenesis solely from inflation is quite challenging. We therefore study a
    model in which a non-inflaton field $\chi$ coupled to the electromagnetic field
    through its kinetic term, $-I^2(\chi) F^2 /4$, continues to move after
    inflation until the completion of reheating. This leads to a post-inflationary
    amplification of the electromagnetic field. We compute all the relevant
    contributions to the curvature perturbation, including gravitational
    interactions, and impose the constraints from the CMB scalar fluctuations on
    the strength of magnetic fields. We, for the first time, explicitly verify both
    the backreaction and CMB constraints in a simple yet successful magnetogenesis
    scenario without invoking a dedicated low-scale inflationary model in the
    weak-coupling regime of the kinetic coupling model.

    DOI

  • Large-scale magnetic fields can explain the baryon asymmetry of the Universe

    Tomohiro Fujita, Kohei Kamada

    Physical Review D   93 ( 8 )  2016年02月

     概要を見る

    Helical hypermagnetic fields in the primordial Universe can produce the
    observed amount of baryon asymmetry through the chiral anomaly without any
    ingredients beyond the standard model of particle physics. While they generate
    no $B-L$ asymmetry, the generated baryon asymmetry survives the spharelon
    washout effect, because the generating process remains active until the
    electroweak phase transition. Solving the Boltzmann equation numerically and
    finding an attractor solution, we show that the baryon asymmetry of our
    Universe can be explained, if the present large-scale magnetic fields indicated
    by the blazar observations have a negative helicity and existed in the early
    Universe before the electroweak phase transition. We also derive the upper
    bound on the strength of the helical magnetic field, which is tighter than the
    cosmic microwave background constraint, to avoid the overproduction of baryon
    asymmetry.

    DOI

  • Spatially covariant theories of gravity: disformal transformation, cosmological perturbations and the Einstein frame

    Tomohiro Fujita, Xian Gao, Jun'ichi Yokoyama

    Journal of Cosmology and Astroparticle Physics   2016 ( 2 )  2015年11月

     概要を見る

    We investigate the cosmological background evolution and perturbations in a
    general class of spatially covariant theories of gravity, which propagates two
    tensor modes and one scalar mode. We show that the structure of the theory is
    preserved under the disformal transformation. We also evaluate the primordial
    spectra for both the gravitational waves and the curvature perturbation, which
    are invariant under the disformal transformation. Due to the existence of
    higher spatial derivatives, the quadratic Lagrangian for the tensor modes
    itself cannot be transformed to the form in the Einstein frame. Nevertheless,
    there exists a one-parameter family of frames in which the spectrum of the
    gravitational waves takes the standard form in the Einstein frame.

    DOI

  • Consistent generation of magnetic fields in axion inflation models

    Tomohiro Fujita, Ryo Namba, Yuichiro Tada, Naoyuki Takeda, Hiroyuki Tashiro

    Journal of Cosmology and Astroparticle Physics   2015 ( 5 )  2015年03月

     概要を見る

    There has been a growing evidence for the existence of magnetic fields in the
    extra-galactic regions, while the attempt to associate their origin with the
    inflationary epoch alone has been found extremely challenging. We therefore
    take into account the consistent post-inflationary evolution of the magnetic
    fields that are originated from vacuum fluctuations during inflation. In the
    model of our interest, the electromagnetic (EM) field is coupled to a
    pseudo-scalar inflaton $\phi$ through the characteristic term $\phi F\tilde F$,
    breaking the conformal invariance. This interaction dynamically breaks the
    parity and enables a continuous production of only one of the polarization
    states of the EM field through tachyonic instability. The produced magnetic
    fields are thus helical. We find that the dominant contribution to the observed
    magnetic fields in this model comes from the modes that leave the horizon near
    the end of inflation, further enhanced by the tachyonic instability right after
    the end of inflation. The EM field is subsequently amplified by parametric
    resonance during the period of inflaton oscillation. Once the thermal plasma is
    formed (reheating), the produced helical magnetic fields undergo a turbulent
    process called inverse cascade, which shifts their peak correlation scales from
    smaller to larger scales. We consistently take all these effects into account
    within the regime where the perturbation of $\phi$ is negligible and obtain
    $B_{\rm eff} \sim 10^{-19}$G, indicating the necessity of additional mechanisms
    to accommodate the observations.

    DOI

  • Can a spectator scalar field enhance inflationary tensor mode?

    Tomohiro Fujita, Jun'ichi Yokoyama, Shuichiro Yokoyama

    Progress of Theoretical and Experimental Physics   2015 ( 4 )  2014年11月

     概要を見る

    We consider the possibility of enhancing the inflationary tensor mode by
    introducing a spectator scalar field with a small sound speed which induces
    gravitational waves as a second order effect. We analytically obtain the power
    spectra of gravitational waves and curvature perturbation induced by the
    spectator scalar field. We found that the small sound speed amplifies the
    curvature perturbation much more than the tensor mode and the current
    observational constraint forces the induced gravitational waves to be
    negligible compared with those from the vacuum fluctuation during inflation.

    DOI

  • Probing Beyond Standard Model via Hawking Radiated Gravitational Waves

    Tomohiro Fujita

       2014年07月

     概要を見る

    We propose a novel technique to probe the beyond standard model (BSM) of
    particle physics. The mass spectrum of unknown BSM particles can be scanned by
    observing gravitational waves (GWs) emitted by Hawking radiation of black
    holes. This is because information on the radiation of the BSM particles is
    imprinted in the spectrum of the GWs. We fully calculate the GW spectrum from
    evaporating black holes taking into account the greybody factor. As an
    observationally interesting application, we consider primordial black holes
    which evaporate in the very early universe. In that case, since the frequencies
    of GWs are substantially redshifted, the GWs emitted with the BSM energy scales
    become accessible by observations.

  • Non-perturbative approach for curvature perturbations in stochastic-$δN$ formalism

    Tomohiro Fujita, Masahiro Kawasaki, Yuichiro Tada

    Journal of Cosmology and Astroparticle Physics   2014 ( 10 )  2014年05月

     概要を見る

    In our previous paper, we have proposed a new algorithm to calculate the
    power spectrum of the curvature perturbations generated in inflationary
    universe with use of the stochastic approach. Since this algorithm does not
    need the perturbative expansion with respect to the inflaton fields on
    super-horizon scale, it works even in highly stochastic cases. For example,
    when the curvature perturbations are very large or the non-Gaussianities of the
    curvature perturbations are sizable, the perturbative expansion may break down
    but our algorithm enables to calculate the curvature perturbations. We apply it
    to two well-known inflation models, chaotic and hybrid inflation, in this
    paper. Especially for hybrid inflation, while the potential is very flat around
    the critical point and the standard perturbative computation is problematic, we
    successfully calculate the curvature perturbations.

    DOI

  • Curvaton in large field inflation

    Tomohiro Fujita, Masahiro Kawasaki, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2014 ( 9 )  2014年04月

     概要を見る

    We comprehensively explore the quadratic curvaton models in the chaotic
    inflation. In the light of the BICEP2 result $r \approx 0.2$, all model
    parameters and relevant observables are computed. It is found the curvaton
    field value is constrained into a narrow range, $\sigma_* =
    \mathcal{O}(10^{-2}$-$10^{-1})$ and the running of the spectral index is $n_s'
    \gtrsim -10^{-3}$. We show that if the curvaton is added, the models are
    heavily degenerated on the $n_s$ - $r$ plane. However, introducing a new plane,
    the degeneracy can be resolved. To distinguish the curvaton models, precise
    measurements of not only $r$ but also $n_s'$ and the tensor tilt $n_T$ are
    required.

    DOI

  • Is there supercurvature mode of massive vector field in open inflation?

    Daisuke Yamauchi, Tomohiro Fujita, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   2014 ( 3 )  2014年02月

     概要を見る

    We investigate the Euclidean vacuum mode functions of a massive vector field
    in a spatially open chart of de Sitter spacetime. In the one-bubble open
    inflationary scenario that naturally predicts a negative spatial curvature
    after a quantum tunneling, it is known that a light scalar field has the
    so-called supercurvature mode, i.e. an additional discrete mode which describes
    fluctuations over scales larger than the spatial curvature scale. If such
    supercurvature modes exist for a vector field with a sufficiently light mass,
    then they would decay slower and easily survive the inflationary era. However,
    the existence of supercurvature mode strongly depends on details of the system.
    To clarify whether a massive vector field has supercurvature modes, we consider
    a U(1) gauge field with gauge and conformal invariances spontaneously broken
    through the Higgs mechanism, and present explicit expressions for the Euclidean
    vacuum mode functions. We find that, for any values of the vector field mass,
    there is no supercurvature mode. In the massless limit, the absence of
    supercurvature modes in the scalar sector stems from the gauge symmetry.

    DOI

  • Critical constraint on inflationary magnetogenesis

    Tomohiro Fujita, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2014 ( 3 )  2014年02月

     概要を見る

    Recently, there are several reports that the cosmic magnetic fields on Mpc
    scale in void region is larger than $\sim 10^{-15}$G with an uncertainty of a
    few orders from the current blazar observations. On the other hand, in
    inflationary magnetogenesis models, additional primordial curvature
    perturbations are inevitably produced from iso-curvature perturbations due to
    generated electromagnetic fields. We explore such induced curvature
    perturbations in a model independent way and obtained a severe upper bound for
    the energy scale of inflation from the observed cosmic magnetic fields and the
    observed amplitude of the curvature perturbation, as $\rho_{\rm inf}^{1/4} <
    30{\rm GeV} \times (B_{\rm obs}/10^{-15}{\rm G})^{-1}$ where $B_{\rm obs}$ is
    the strength of the magnetic field at present. Therefore, without a dedicated
    low energy inflation model or an additional amplification of magnetic fields
    after inflation, inflationary magnetogenesis on Mpc scale is generally
    incompatible with CMB observations.

    DOI

  • Void magnetic field and its primordial origin in inflation

    Tomohiro Fujita

       2014年01月

     概要を見る

    Since magnetic fields in galaxies, galactic clusters and even void regions
    are observed, theoretical attempts to explain their origin are strongly
    motivated. It is interesting to consider that inflation is responsible for the
    origin of the magnetic fields as well as the density perturbation. However, it
    is known that inflationary magnetogenesis suffers from several problems. We
    explore these problems by using a specific model, namely the kinetic coupling
    model, and show how the model is constrained. Model independent arguments are
    also discussed.

  • Baryon Asymmetry, Dark Matter, and Density Perturbation from PBH

    Tomohiro Fujita, Keisuke Harigaya, Masahiro Kawasaki, Ryo Matsuda

    Physical Review D - Particles, Fields, Gravitation and Cosmology   89 ( 10 )  2014年01月

     概要を見る

    We investigate the consistency of a scenario in which the baryon asymmetry,
    dark matters, as well as the cosmic density perturbation are generated
    simultaneously through the evaporation of primordial black holes (PBHs). This
    scenario can explain the coincidence of the dark matter and the baryon density
    of the universe, and is free from the isocurvature perturbation problem. We
    show that this scenario predicts the masses of PBHs, right-handed neutrinos and
    dark matters, the Hubble scale during inflation, the non-gaussianity and the
    running of the spectral index. We also discuss the testability of the scenario
    by detecting high frequency gravitational waves from PBHs.

    DOI

  • A new algorithm for calculating the curvature perturbations in stochastic inflation

    Tomohiro Fujita, Masahiro Kawasaki, Yuichiro Tada, Tomohiro Takesako

    Journal of Cosmology and Astroparticle Physics   2013 ( 12 )  2013年08月

     概要を見る

    We propose a new approach for calculating the curvature perturbations
    produced during inflation in the stochastic formalism. In our formalism, the
    fluctuations of the e-foldings are directly calculated without perturbatively
    expanding the inflaton field and they are connected to the curvature
    perturbations by the $\delta N$ formalism. The result automatically includes
    the contributions of the higher order perturbations because we solve the
    equation of motion non-perturbatively. In this paper, we analytically prove
    that our result (the power spectrum and the nonlinearity parameter) is
    consistent with the standard result in single field slow-roll inflation. We
    also describe the algorithm for numerical calculations of the curvature
    perturbations in more general inflation models.

    DOI

  • Large Scale Cosmic Perturbation from Evaporation of Primordial Black Holes

    Tomohiro Fujita, Keisuke Harigaya, Masahiro Kawasaki

    Physical Review D - Particles, Fields, Gravitation and Cosmology   88 ( 12 )  2013年06月

     概要を見る

    We present a novel mechanism to generate the cosmic perturbation from
    evaporation of primordial black holes. A mass of a field is fluctuated if it is
    given by a vacuum expectation value of a light scalar field because of the
    quantum fluctuation during inflation. The fluctuated mass causes variations of
    the evaporation time of the primordial black holes. Therefore provided the
    primordial black holes dominate the universe when they evaporate, primordial
    cosmic perturbations are generated. We find that the amplitude of the large
    scale curvature perturbation generated in this scenario can be consistent with
    the observed value. Interestingly, our mechanism works even if all fields which
    are responsible for inflation and the generation of the cosmic perturbation are
    decoupled from the visible sector except for the gravitational interaction. An
    implication to the running spectral index is also discussed.

    DOI

  • Higher order statistics of curvature perturbations in IFF model and its Planck constraints

    Tomohiro Fujita, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2013 ( 9 )  2013年06月

     概要を見る

    We compute the power spectrum P_\zeta, and non-linear parameters f_nl and
    \tau_nl of the curvature perturbation induced during inflation by the
    electromagnetic fields in the kinetic coupling model (IFF model). By using the
    observational result of P_\zeta, f_nl and \tau_nl reported by the Planck
    collaboration, we study the constraint on the model comprehensively.
    Interestingly, if the single slow-rolling inflaton is responsible for the
    observed P_\zeta, the constraint from \tau_nl is most stringent. We also find a
    general relationship between f_nl and \tau_nl generated in this model. Even if
    f_nl \sim O(1), a detectable \tau_nl can be produced.

    DOI

  • Universal upper limit on inflation energy scale from cosmic magnetic field

    Tomohiro Fujita, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   2012 ( 10 )  2012年05月

     概要を見る

    Recently observational lower bounds on the strength of cosmic magnetic fields
    were reported, based on gamma-ray flux from distant blazars. If inflation is
    responsible for the generation of such magnetic fields then the inflation
    energy scale is bounded from above as rho_{inf}^{1/4} < 2.5 times 10^{-7}M_{Pl}
    times (B_{obs}/10^{-15}G)^{-2} in a wide class of inflationary magnetogenesis
    models, where B_{obs} is the observed strength of cosmic magnetic fields. The
    tensor-to-scalar ratio is correspondingly constrained as r< 10^{-19} times
    (B_{obs}/10^{-15}G)^{-8}. Therefore, if the reported strength B_{obs} \geq
    10^{-15}G is confirmed and if any signatures of gravitational waves from
    inflation are detected in the near future, then our result indicates some
    tensions between inflationary magnetogenesis and observations.

    DOI

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受賞

  • 若手奨励賞(宇宙線・宇宙物理領域)

    2022年03月   日本物理学会   ゲージ場の宇宙論  

講演・口頭発表等

  • 日本物理学会 第16回 若手奨励賞 受賞記念講演「ゲージ場の宇宙論」

    藤田智弘  [招待有り]

    日本物理学会  

    発表年月: 2022年03月

    開催年月:
    2022年03月
     
     
  • SU(N)-natural inflationにおける原始重力波生成

    藤田智弘

    第1回「素粒子と重力波」研究会  

    発表年月: 2022年02月

    開催年月:
    2022年02月
     
     
  • SU(N) gauge-natural inflation

    Tomohiro Fujita

    Yukawa International Seminar 2022a "Gravity - The Next Generation-"  

    発表年月: 2022年02月

    開催年月:
    2022年02月
     
     
  • Cosmic Birefringence and Axion Dark Energy

    Tomohiro Fujita  [招待有り]

    8th Korea-Japan workshop on Dark Energy  

    発表年月: 2021年10月

    開催年月:
    2021年10月
     
     
  • SU(N) chromo-natural inflation

    藤田智弘, 中塚洋佑, 向田享平, 村井開

    日本物理学会  

    発表年月: 2021年09月

    開催年月:
    2021年09月
     
     
 

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