2022/10/02 更新

写真a

ヤマダ ユウスケ
山田 悠介
Scopus 論文情報  
論文数: 0  Citation: 0  h-index: 13

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)

経歴

  • 2019年04月
    -
    2022年03月

    東京大学   大学院理学系研究科附属ビッグバン宇宙国際研究センター   日本学術振興会特別研究員PD

  • 2016年10月
    -
    2019年03月

    スタンフォード大学   理論物理学研究所   ポスドク研究員

  • 2016年04月
    -
    2016年09月

    慶應義塾大学   自然科学研究教育センター   ポスドク研究員

 

論文

  • Goldstino Condensation?

    Renata Kallosh, Andrei Linde, Timm Wrase, Yusuke Yamada

       2022年06月

     概要を見る

    It was argued in \cite{DallAgata:2022abm} that the Volkov-Akulov (VA) model
    as well as similar models in supergravity and the related KKLT model in string
    theory, suffer from tachyonic instabilities due to goldstino condensation. The
    authors of \cite{DallAgata:2022abm} constructed a specific model with two
    unconstrained interacting chiral superfields with linearly realized
    supersymmetry which has an unstable vacuum. They claimed that this model
    becomes equivalent to the VA model in the UV limit. We show that the UV limit
    of their model is discontinuous, and the vacuum instability of the model
    proposed in \cite{DallAgata:2022abm} is not relevant to the VA model, to
    related models in supergravity, and to the KKLT construction.

    DOI

    Scopus

  • IIB String Theory and Sequestered Inflation

    Renata Kallosh, Andrei Linde, Timm Wrase, Yusuke Yamada

       2021年08月

     概要を見る

    We develop sequestered inflation models, where inflation occurs along flat
    directions in supergravity models derived from type IIB string theory. It is
    compactified on a ${\mathbb{T}^6 \over \mathbb{Z}_2 \times \mathbb{Z}_2}$
    orientifold with generalized fluxes and O3/O7-planes. At Step I, we use flux
    potentials which 1) satisfy tadpole cancellation conditions and 2) have
    supersymmetric Minkowski vacua with flat direction(s). The 7 moduli are split
    into heavy and massless Goldstone multiplets. At Step II we add a nilpotent
    multiplet and uplift the flat direction(s) of the type IIB string theory to
    phenomenological inflationary plateau potentials: $\alpha$-attractors with 7
    discrete values $3\alpha = 1, 2, 3, ..., 7$. Their cosmological predictions are
    determined by the hyperbolic geometry inherited from string theory. The masses
    of the heavy fields and the volume of the extra dimensions change during
    inflation, but this does not affect the inflationary dynamics.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Sequestered Inflation

    Renata Kallosh, Andrei Linde, Timm Wrase, Yusuke Yamada

       2021年08月

     概要を見る

    We construct supergravity models allowing to sequester the phenomenology of
    inflation from the Planckian energy scale physics. The procedure consists of
    two steps: At Step I we study supergravity models, which might be associated
    with string theory or M-theory, and have supersymmetric Minkowski vacua with
    flat directions. At Step II we uplift these flat directions to inflationary
    plateau potentials. We find certain conditions which ensure that the superheavy
    fields involved in the stabilization of the Minkowski vacua at Step I are
    completely decoupled from the inflationary phenomenology.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Aether SUSY breaking: Can aether be alternative to F-term SUSY breaking?

    Yusuke Yamada

       2021年06月

     概要を見る

    We investigate supersymmetry (SUSY) breaking scenarios where both SUSY and
    Lorentz symmetry are broken spontaneously. For concreteness, we propose models
    in which scalar fluid or vector condensation breaks Lorentz symmetry and
    accordingly SUSY. Then, we examine whether such scenarios are viable for
    realistic model buildings. We find, however, that the scalar fluid model
    suffers from several issues. Then, we extend it to a vector condensation model,
    which avoids the issues in the scalar fluid case. We show that accelerated
    expansion and soft SUSY breaking in matter sector can be achieved. In our
    simple setup, the soft SUSY breaking is constrained to be less than
    $\mathcal{O}(100)$TeV from the constraints on modification of gravity.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Superadiabatic basis in cosmological particle production: application to preheating

    Yusuke Yamada

       2021年06月

     概要を見る

    We discuss the adiabatic basis dependence of particle number in
    time-dependent backgrounds. In particular, we focus on preheating after
    inflation, and show that, for the optimal basis, the time dependence of the
    produced particle number can be well approximated by a simple connection
    formula, which can be obtained by analysing Stokes phenomenon in given
    backgrounds. As we show explicitly, the simple connection formula can describe
    various parameter regions such as narrow and broad resonance regime in a
    unified manner.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Chiral gravitational effect in time-dependent backgrounds

    Kohei Kamada, Jun'ya Kume, Yusuke Yamada

       2021年04月

     概要を見る

    Gravitational counterpart of the chiral magnetic effect, which is referred as
    the chiral gravitational effect, can also be of interest in a cosmological
    setup. In this study, we investigate this effect in the time-dependent chiral
    asymmetric fermion background and in the expanding spacetime by formulating the
    effective action of gravitational waves. We also analyze the anomaly equation
    to see how the backreaction from gravitational waves to thermal chiral plasma
    occurs. We find that the non-trivial time dependence of chiral chemical
    potential, which can be induced in some scenarios of baryogenesis, is the key
    ingredient of the chiral gravitational effect. It turns out that the "memory"
    of the effect is imprinted on the high frequency gravitational waves
    propagating in the plasma. Cosmological implications and potential effects on
    the gravitational wave observation are briefly discussed.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Stokes phenomenon and gravitational particle production -- How to evaluate it in practice

    Soichiro Hashiba, Yusuke Yamada

       2021年01月

     概要を見る

    We revisit gravitational particle production from the Stokes phenomenon
    viewpoint, which helps us make a systematic way to understand asymptotic
    behavior of mode functions in time-dependent background. One of our purposes of
    this work is to make the method more practical for evaluation of
    non-perturbative particle production rate. In particular, with several examples
    of time-dependent backgrounds, we introduce some approximation methods that
    make the analysis more practical. Specifically, we consider particle production
    in simple expanding backgrounds, preheating after $R^2$ inflation, and a
    transition model with smoothly changing mass. As we find several technical
    issues in analyzing the Stokes phenomenon of each example, we discuss how to
    simplify the problems while showing the accuracy of analytic estimation under
    the approximations we make.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • M-theory Cosmology, Octonions, Error Correcting Codes

    Murat Gunaydin, Renata Kallosh, Andrei Linde, Yusuke Yamada

       2020年08月

     概要を見る

    We study M-theory compactified on twisted 7-tori with $G_2$-holonomy. The
    effective 4d supergravity has 7 chiral multiplets, each with a unit logarithmic
    K\"ahler potential. We propose octonion, Fano plane based superpotentials,
    codifying the error correcting Hamming (7,4) code. The corresponding 7-moduli
    models have Minkowski vacua with one flat direction. We also propose
    superpotentials based on octonions/error correcting codes for Minkowski vacua
    models with two flat directions. We update phenomenological $\alpha$-attractor
    models of inflation with $3\alpha=7,6,5,4,3,1$, based on inflation along these
    flat directions. These inflationary models reproduce the benchmark targets for
    detecting B-modes, predicting 7 different values of $r = 12\alpha/N_{e}^{2}$ in
    the range $10^{-2}\gtrsim r \gtrsim 10^{-3}$, to be explored by future
    cosmological observations.

    DOI

    Scopus

    6
    被引用数
    (Scopus)
  • Renormalization in gravitational leptogenesis with pseudo-scalar-tensor coupling

    Kohei Kamada, Jun'ya Kume, Yusuke Yamada

       2020年07月

     概要を見る

    We consider the renormalization in the pseudo-scalar inflation models with
    the gravitational Chern-Simons term. In this model, lepton asymmetry is
    generated from the chiral gravitational waves produced due to the Chern-Simons
    term through the gravitational chiral anomaly. However, it is known that the
    naive estimate of the expectation value of the gravitational Chern-Pontryagin
    density as well as the resultant lepton number density depend on the UV-cutoff
    scale, which raises a question on their validity. In this paper, we propose a
    way to renormalize the expectation value of the Chern-Pontryagin density to
    remove the UV-cutoff dependence. We also discuss the renormalized lepton number
    density when we adopt the minimal subtraction scheme and the viability of the
    gravitational leptogenesis scenario.

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Particle production induced by vacuum decay in real time dynamics

    Soichiro Hashiba, Yusuke Yamada, Jun'ichi Yokoyama

       2020年06月

     概要を見る

    We discuss particle production associated with vacuum decay, which changes
    the mass of a scalar field coupled to a background field which induces the
    decay. By utilizing the Stokes phenomenon, we can optimally track the
    time-evolution of mode function and hence calculate particle production
    properly. In particular, we use real time formalisms for vacuum decay in
    Minkowski and de Sitter spacetime together with the Stokes phenomenon method.
    For each case, we consider the flyover vacuum decay model and stochastic
    inflation, respectively. Within the real time formalism, the particle
    production can be viewed as that caused by nontrivial external fields. This
    gives us a novel perspective of the real time formalism of vacuum decay.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Gravitational leptogenesis with kination and gravitational reheating

    Kohei Kamada, Jun'ya Kume, Yusuke Yamada, Jun'ichi Yokoyama

       2019年11月

     概要を見る

    We revisit the gravitational leptogenesis scenario in which the inflaton is
    coupled to gravity by the Chern-Simons term and the lepton asymmetry is
    generated through the gravitational anomaly in the lepton number current during
    inflation. We constrain the possible model parameter space by requiring the
    absence of ghost modes below the Planck scale, which would suggest the
    breakdown of the effective theory, and evaluate the net baryon asymmetry for
    various reheating processes. We find that the mechanism with these requirements
    is insufficient to explain the observed baryon asymmetry of the Universe for
    standard reheating scenarios. We show that, however, with the kination scenario
    realized in e.g. the k- and G-inflation models, a sufficient baryon asymmetry
    can be generated within a feasible range of the model parameters.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Horndeski model in nonlinearly realized supergravity

    Yusuke Yamada, Jun'ichi Yokoyama

       2019年06月

     概要を見る

    We construct the Horndeski Lagrangian within non-linearly realized
    supergravity. We will show that the bosonic part of the Horndeski Lagrangian
    can be realized. Gravitino naturally couples to Horndeski sector in a
    super-covariant way. Such gravitino couplings are also free from ghosts.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • The supersymmetric anti-D3-brane action in KKLT

    Niccolò Cribiori, Christoph Roupec, Timm Wrase, Yusuke Yamada

       2019年06月

     概要を見る

    An anti-D3-brane plays a crucial role in the construction of semi-realistic
    cosmological models in string theory. Part of its action provides an uplift
    term that has been used to lift AdS solutions to phenomenologically viable dS
    vacua in the KKLT and LVS setups. In the last few years it has been shown that
    this uplift breaks supersymmetry spontaneously and can be described in the 4d
    $\mathcal{N}=1$ supergravity language by using constrained supermultiplets.
    Here we derive the complete 4d $\mathcal{N}=1$ supergravity action for an
    anti-D3-brane coupled to all closed string background fields. In particular we
    include the vector field, the scalar fields and all fermions that live on the
    anti-D3-brane.

    DOI

    Scopus

    24
    被引用数
    (Scopus)
  • Off-shell $N=2\to N=1$ reduction in 4D conformal supergravity

    Yusuke Yamada

       2019年01月

     概要を見る

    We discuss $N=2\to N=1$ reduction in four dimensional conformal supergravity.
    In particular, we keep the off-shell structure of supermultiplets (except
    hypermultiplets). As we will show, starting with (almost) off-shell conformal
    supergravity makes the procedure simpler than that from $N=2$ Poincar\'e
    supergravity, which makes it easier to show the correspondence to the standard
    $N=1$ conformal supergravity. We find that the $N=1$ superconformal symmetry is
    simply realized by truncating the gravitino multiplet. We also discuss the
    consistency with the original $N=2$ system and show the reduced $N=1$ conformal
    supergravity action.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Simple Sinflaton-less $α$-attractors

    Renata Kallosh, Yusuke Yamada

       2019年01月

     概要を見る

    We construct the simplest inflationary $\alpha$-attractor models in
    supergravity: it has only one scalar, the inflaton. There is no sinflaton since
    the inflaton belongs to an orthogonal nilpotent superfield where the sinflaton
    depends on fermion bilinears. When the local supersymmetry is gauge-fixed,
    these models have only one single real scalar (the inflaton), a graviton and a
    massive gravitino. The sinflaton, sgoldstino and inflatino are all absent from
    the physical spectrum in the unitary gauge. The orthogonality condition leads
    to the simplest K\"ahler potential for the inflaton, while preserving the
    Poincar\'e disk geometry of $\alpha$-attractors. The models are particularly
    simple in the framework of the $\overline {D3}$ induced geometric inflation.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Planck 2018 and Brane Inflation Revisited

    Renata Kallosh, Andrei Linde, Yusuke Yamada

       2018年11月

     概要を見る

    We revisit phenomenological as well as string-theoretical aspects of D-brane
    inflation cosmological models. Phenomenologically these models stand out on par
    with $\alpha$-attractors, as models with Planck-compatible values of $n_s$,
    moving down to the sweet spot in the data with decreasing value of $r$. On the
    formal side we present a new supersymmetric version of these models in the
    context of de Sitter supergravity with a nilpotent multiplet and volume modulus
    stabilization. The geometry of the nilpotent multiplet is evaluated in the
    framework of string theory.

    DOI

    Scopus

    12
    被引用数
    (Scopus)
  • Duality Constraints on Counterterms in $\mathcal N=5,\ 6$ Supergravities

    Daniel Z. Freedman, Renata Kallosh, Yusuke Yamada

       2018年07月

     概要を見る

    The UV finiteness found in calculations of the 4-point amplitude in $\mathcal
    N=5$ supergravity at loop order $L=3, 4$ has not been explained, which
    motivates our study of the relevant superspace invariants and on-shell
    superamplitudes for both $\mathcal N=5$ and $\mathcal N=6$. The local 4-point
    superinvariants for $L = 3,4$ are expected to have nonlinear completions whose
    6-point amplitudes have non-vanishing SSL's (soft scalar limits), violating the
    behavior required of Goldstone bosons. For $\mathcal N=5$, we find at $L=3$
    that local 6-point superinvariant and superamplitudes, which might cancel these
    SSL's, do not exist. This rules out the candidate 4-point counterterm and thus
    gives a plausible explanation of the observed $L=3$ finiteness. However, at $L=
    4$ we construct a local 6-point superinvariant with non-vanishing SSL's, so the
    SSL argument does not explain the observed $L=4$ $\mathcal N=5$ UV finiteness.
    For $\mathcal N=6$ supergravity there are no 6-point invariants at either $L=
    3$ or 4, so the SSL argument predicts UV finiteness.

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Hypernatural inflation

    Andrei Linde, Dong-Gang Wang, Yvette Welling, Yusuke Yamada, Ana Achucarro

       2018年03月

     概要を見る

    We constructed a model of natural inflation in the context of
    $\alpha$-attractor supergravity, in which both the dilaton field and the axion
    field are light during inflation, and the inflaton may be a combination of the
    two. The T-model version of this theory is defined on the Poincare disk with
    radius |Z| = 1. It describes a Mexican hat potential with the flat axion
    direction corresponding to a circle of radius |Z| < 1. The axion decay constant
    $f_{a}$ in this theory can be exponentially large because of the hyperbolic
    geometry of the Poincare disk. Depending on initial conditions, this model may
    describe $\alpha$-attractor inflation driven by the radial component of the
    inflaton field, natural inflation driven by the axion field, or a sequence of
    these two regimes. We also construct the E-model version of this theory, which
    has similar properties. In addition, we describe generalized $\alpha$-attractor
    models where the potential can be singular at the boundary of the moduli space,
    and show that they can provide a simple solution for the problem of initial
    conditions for the models with plateau potentials.

    DOI

    Scopus

    24
    被引用数
    (Scopus)
  • Supertrace formulae for nonlinearly realized supersymmetry

    Divyanshu Murli, Yusuke Yamada

       2018年03月

     概要を見る

    We derive the general supertrace formula for a system with $N$ chiral
    superfields and one nilpotent chiral superfield in global and local
    supersymmetry. The nilpotent multiplet is realized by taking the
    scalar-decoupling limit of a chiral superfield breaking supersymmetry
    spontaneously. As we show, however, the modified formula is not simply related
    to the scalar-decoupling limit of the supertrace in linearly-realized
    supersymmetry. We also show that the supertrace formula reduces to that of a
    linearly realized supersymmetric theory with a decoupled sGoldstino if the
    Goldstino is the fermion in the nilpotent multiplet.

    DOI

    Scopus

  • U(1) symmetric $α$-attractors

    Yusuke Yamada

       2018年02月

     概要を見る

    We present a class of supergravity $\alpha$-attractors with an approximate
    global U(1) symmetry corresponding to the axion direction. We also develop a
    multi-field generalization of these models and show that the $\alpha$-attractor
    models with U(1) symmetries have a dual description in terms of a two-form
    superfield coupled to a three-form superfield.

    DOI

    Scopus

    10
    被引用数
    (Scopus)
  • On quantum compatibility of counterterm deformations and duality symmetries in ${\cal N}\geq 5$ supergravities

    Renata Kallosh, Hermann Nicolai, Radu Roiban, Yusuke Yamada

       2018年02月

     概要を見る

    In ${\cal N}=5, 6, 8$ supergravities there are hidden symmetries of equations
    of motion, described by duality groups $SU(1,5), \, SO^*(12), \, E_{7(7)}$
    respectively. UV divergences and known candidate counterterms violate the
    deformed duality symmetry current conservation. Extra higher derivative terms
    in the action are required to restore duality. We study the effect of a
    two-vector part of the counterterm for ${\cal N}\geq 5$ supergravities using
    the universality of the symplectic structure of extended supergravities. We
    construct a compact form of a deformed action with infinite number of higher
    derivative terms and restored duality symmetry with deformation parameter
    $\lambda$. We find, in $\lambda^2$ approximation, that the $SU({\cal N})$
    symmetry of the deformed theory is restored on shell.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Ghostbusters in $f(R)$ supergravity

    Toshiaki Fujimori, Muneto Nitta, Keisuke Ohashi, Yusuke Yamada

    Journal of High Energy Physics   2018 ( 5 )  2017年12月

     概要を見る

    $f(R)$ supergravity is known to contain a ghost mode associated with
    higher-derivative terms if it contains $R^n$ with $n$ greater than two.We
    remove the ghost in $f(R)$ supergravity by introducing auxiliary gauge field to
    absorb the ghost. We dub this method as the ghostbuster
    mechanism~\cite{Fujimori:2016udq}. We show that the mechanism removes the ghost
    supermultiplet but also terms including $R^n$ with $n\geq3$, after integrating
    out auxiliary degrees of freedom. For pure supergravity case, there appears an
    instability in the resultant scalar potential. We then show that the
    instability of the scalar potential can be cured by introducing matter
    couplings in such a way that the system has a stable potential.

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Internal Supersymmetry and Small-field Goldstini

    Diederik Roest, Pelle Werkman, Yusuke Yamada

       2017年10月

     概要を見る

    The dynamics of the Goldstino mode of spontaneously broken supersymmetry is
    universal, being fully determined by the non-linearly realized symmetry. We
    investigate the small-field limit of this theory. This model non-linearly
    realizes an alternative supersymmetry algebra with vanishing anti-commutators
    between the fermionic generators, much like an internal supersymmetry. This
    Goldstino theory is akin to the Galilean scalar field theory that arises as the
    small-field limit of Dirac-Born-Infeld theory and non-linearly realizes the
    Galilean symmetry. Indeed, the small-field Goldstino is the partner of a
    complex Galilean scalar field under conventional supersymmetry. We close with
    the generalization to extended internal supersymmetry and a discussion of its
    higher-dimensional origin.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Gravitino Problem in Inflation Driven by Inflaton-Polonyi Kähler Coupling

    Fuminori Hasegawa, Kazunori Nakayama, Takahiro Terada, Yusuke Yamada

       2017年09月

     概要を見る

    We discuss the cosmological gravitino problem in inflation models in which
    the inflaton potential is constructed from K\"ahler potential rather than
    superpotential: a representative model is $\overline{\text{D}3}$-induced
    geometric inflation. A critical ingredient in this type of models is the
    coupling of the inflaton and Polonyi (supersymmetry-breaking) field in the
    K\"ahler potential, which is needed to build the inflaton potential. We point
    out the same coupling let the inflaton dominantly decay into a pair of
    inflatino and gravitino causing the gravitino problem. We propose some possible
    solutions to this problem.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Ghost-free vector superfield actions in supersymmetric higher-derivative theories

    Toshiaki Fujimori, Muneto Nitta, Keisuke Ohashi, Yusuke Yamada, Ryo Yokokura

    Journal of High Energy Physics   2017 ( 9 )  2017年08月

     概要を見る

    We systematically construct ghost-free higher-derivative actions of Abelian
    vector supermultiplets in four-dimensional ${\cal N}=1$ global supersymmetric
    theories. After giving a simple example which illustrates that a naive
    introduction of a higher-derivative term gives rise to a ghost, we discuss
    possible building blocks for a ghost-free action and explicitly show that their
    bosonic parts have no ghost mode and the auxiliary field $\boldsymbol{D}$ does
    not propagate. Higher-derivative terms yield higher powers of the auxiliary
    field $\boldsymbol{D}$ in the actions, and the D-term equations of motion
    consequently admit multiple solutions in general. We confirm that the
    well-known supersymmetric Dirac-Born-Infeld action falls into this class. We
    further give another example in which the standard quadratic kinetic term
    (Maxwell term) is corrected by a quartic term of the field strength. We also
    discuss possible couplings to matter fields and a deformed D-term potential.

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Fibre Inflation and $α$-attractors

    Renata Kallosh, Andrei Linde, Diederik Roest, Alexander Westphal, Yusuke Yamada

       2017年07月

     概要を見る

    Fibre inflation is a specific string theory construction based on the Large
    Volume Scenario that produces an inflationary plateau. We outline its relation
    to $\alpha$-attractor models for inflation, with the cosmological sector
    originating from certain string theory corrections leading to $\alpha=2$ and
    $\alpha=1/2$. Above a certain field range, the steepening effect of
    higher-order corrections leads first to the breakdown of single-field slow-roll
    and after that to the onset of 2-field dynamics: the overall volume of the
    extra dimensions starts to participate in the effective dynamics. Finally, we
    propose effective supergravity models of fibre inflation based on an
    ${\overline {D3 } }$ uplift term with a nilpotent superfield. Specific moduli
    dependent $\overline {D3}$ induced geometries lead to cosmological fibre models
    but have in addition a de Sitter minimum exit. These supergravity models
    motivated by fibre inflation are relatively simple, stabilize the axions and
    disentangle the Hubble parameter from supersymmetry breaking.

    DOI

    Scopus

    20
    被引用数
    (Scopus)
  • $\overline{D3}$ Induced Geometric Inflation

    Renata Kallosh, Andrei Linde, Diederik Roest, Yusuke Yamada

       2017年05月

     概要を見る

    Effective supergravity inflationary models induced by anti-D3 brane
    interaction with the moduli fields in the bulk geometry have a geometric
    description. The K\"ahler function carries the complete geometric information
    on the theory. The non-vanishing bisectional curvature plays an important role
    in the construction. The new geometric formalism, with the nilpotent superfield
    representing the anti-D3 brane, allows a powerful generalization of the
    existing inflationary models based on supergravity. They can easily incorporate
    arbitrary values of the Hubble parameter, cosmological constant and gravitino
    mass. We illustrate it by providing generalized versions of polynomial chaotic
    inflation, T- and E-models of $\alpha$-attractor type, disk merger. We also
    describe a multi-stage cosmological attractor regime, which we call cascade
    inflation.

    DOI

    Scopus

    43
    被引用数
    (Scopus)
  • Maximal Supersymmetry and B-Mode Targets

    Renata Kallosh, Andrei Linde, Timm Wrase, Yusuke Yamada

       2017年04月

     概要を見る

    Extending the work of Ferrara and one of the authors, we present dynamical
    cosmological models of $\alpha$-attractors with plateau potentials for
    $3\alpha=1,2,3,4,5,6,7$. These models are motivated by geometric properties of
    maximally supersymmetric theories: M-theory, superstring theory, and maximal $N
    = 8$ supergravity. After a consistent truncation of maximal to minimal
    supersymmetry in a seven-disk geometry, we perform a two-step procedure: 1) we
    introduce a superpotential, which stabilizes the moduli of the seven-disk
    geometry in a supersymmetric minimum, 2) we add a cosmological sector with a
    nilpotent stabilizer, which breaks supersymmetry spontaneously and leads to a
    desirable class of cosmological attractor models. These models with $n_s$
    consistent with observational data, and with tensor-to-scalar ratio $r \approx
    10^{-2}- 10^{-3}$, provide natural targets for future B-mode searches. We
    relate the issue of stability of inflationary trajectories in these models to
    tessellations of a hyperbolic geometry.

    DOI

    Scopus

    30
    被引用数
    (Scopus)
  • Absence of U(1) Anomalous Superamplitudes in $\mathcal{N}\geq 5$ Supergravities

    Daniel Z. Freedman, Renata Kallosh, Divyanshu Murli, Antoine Van Proeyen, Yusuke Yamada

       2017年03月

     概要を見る

    We list all potential candidates for U(1) anomalous non-local 1-loop 4-point
    amplitudes and higher loop UV divergences in $\mathcal{N}\geq 5$
    supergravities. The relevant chiral superinvariants are constructed from
    linearized chiral superfields and define the corresponding superamplitudes. The
    anomalous amplitudes, of the kind present in $\mathcal{N}=4$, are shown to be
    absent in $\mathcal{N} \geq 5$. In $\mathcal{N}=6$ supergravity the result is
    deduced from the double-copy $\mathcal{N}=4_{YM} \times (\mathcal{N}=2)_{YM}$
    model, whereas in $\mathcal{N}=5,8$ the result on absence of anomalous
    amplitudes is derived in supergravities as well as in the $(\mathcal{N}=4)_{YM}
    \times (\mathcal{N}-4)_{YM}$ double-copy models.

    DOI

    Scopus

    12
    被引用数
    (Scopus)
  • Gravitino Problem in Minimal Supergravity Inflation

    Fuminori Hasegawa, Kyohei Mukaida, Kazunori Nakayama, Takahiro Terada, Yusuke Yamada

       2017年01月

     概要を見る

    We study non-thermal gravitino production in the minimal supergravity
    inflation. In this minimal model utilizing orthogonal nilpotent superfields,
    the particle spectrum includes only graviton, gravitino, inflaton, and
    goldstino. We find that a substantial fraction of the cosmic energy density can
    be transferred to the longitudinal gravitino due to non-trivial change of its
    sound speed. This implies either a breakdown of the effective theory during
    reheating or a serious gravitino problem.

    DOI

    Scopus

    18
    被引用数
    (Scopus)
  • More on DBI action in 4D $\mathcal{N}=1$ supergravity

    Shuntaro Aoki, Yusuke Yamada

       2016年11月

     概要を見る

    We construct a Dirac-Born-Infeld (DBI) action coupled to a two-form field in
    four dimensional $\mathcal{N}=1$ supergravity. Our superconformal formulation
    of the action shows a universal way to construct it in various Poincar\'e
    supergravity formulations. We generalize the DBI action to that coupled to
    matter sector. We also discuss duality transformations of the DBI action, which
    are useful for phenomenological and cosmological applications.

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Note on "Equivalence Between Different Auxiliary Field Formulations of ${\cal N}=1$ Supergravity Coupled to Matter"

    Shuntaro Aoki, Yusuke Yamada

       2016年09月

     概要を見る

    In the version 1 of this paper, we claimed that 4D ${\cal N}=1$ supergravity
    formulations with different auxiliary fields can be unified using U(1) gauge
    symmetry, whose gauge superfield does not have a kinetic term. However, after
    submission, we found a critical error in our statement. This is the note on the
    paper of the version 1.

  • Ghostbusters in higher derivative supersymmetric theories: who is afraid of propagating auxiliary fields?

    Toshiaki Fujimori, Muneto Nitta, Yusuke Yamada

    Journal of High Energy Physics   2016 ( 9 )  2016年08月

     概要を見る

    We present for the first time a ghost-free higher-derivative chiral model
    with a propagating auxiliary F-term field (highest component of the chiral
    multiplet). We obtain this model by removing a ghost in a higher derivative
    chiral model, with Higgsing it in terms of an auxiliary vector superfield.
    Depending on the sign of the quadratic derivative term of the chiral
    superfield, the model contains two ghost free branches of the parameter
    regions. We find that supersymmetry is spontaneously broken in one branch while
    it is preserved in the other branch. As a consequence of dynamical F-term
    field, a conserved U(1) charge corresponding to the number density of $F$
    appears, which can be regarded as a generalization of the R-symmetry.

    DOI

    Scopus

    22
    被引用数
    (Scopus)
  • Cosmological relaxation and high scale inflation

    Tetsutaro Higaki, Naoyuki Takeda, Yusuke Yamada

       2016年07月

     概要を見る

    We study whether the relaxion mechanism solves the Higgs hierarchy problem
    against a high scale inflation or a high reheating temperature. To accomplish
    the mechanism, we consider the scenario that the Higgs vacuum expectation value
    is determined after inflation. We take into account the effects of the Hubble
    induced mass and thermal one in the dynamics of the relaxion.

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Abelian tensor hierarchy in 4D ${\cal N}=1$ conformal supergravity

    Shuntaro Aoki, Tetsutaro Higaki, Yusuke Yamada, Ryo Yokokura

       2016年06月

     概要を見る

    We consider Abelian tensor hierarchy in four-dimensional ${\cal N}=1$
    supergravity in the conformal superspace formalism, where the so-called
    covariant approach is used to antisymmetric tensor fields. We introduce
    $p$-form gauge superfields as superforms in the conformal superspace. We solve
    the Bianchi identities under the constraints for the superforms. As a result,
    each of form fields is expressed by a single gauge invariant superfield. The
    action of superforms is shown with the invariant superfields. We also show the
    relation between the superspace formalism and the superconformal tensor
    calculus.

    DOI

    Scopus

    14
    被引用数
    (Scopus)
  • DBI action of real linear superfield in 4D ${\cal N}=1$ conformal supergravity

    Shuntaro Aoki, Yusuke Yamada

       2016年03月

     概要を見る

    We construct the Dirac-Born-Infeld (DBI) action of a real linear multiplet in
    4D $\mathcal{N}=1$ supergravity. Based on conformal supergravity, we derive the
    general condition under which the DBI action can be realized, and show that it
    can be constructed in the new minimal supergravity. We also generalize it to
    the matter coupled system.

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • de Sitter vacuum from $R^2$ supergravity

    Fuminori Hasegawa, Yusuke Yamada

       2015年09月

     概要を見る

    We propose a supergravity model with a constrained curvature multiplet, which
    realizes the Starobinsky inflation and the de Sitter vacuum in the present
    universe simultaneously. Surprisingly, at the vacuum, the soft supersymmetry
    breaking scale for minimal supersymmetric standard model sector becomes the TeV
    scale, however, the gravitino mass scale becomes much higher than that of soft
    supersymmetry breaking. Such a hierarchical structure, which naturally avoids
    the gravitino problem, appears without introducing a new scale other than
    inflation scale.

    DOI

    Scopus

    12
    被引用数
    (Scopus)
  • N=1 superfield description of six-dimensional supergravity

    Hiroyuki Abe, Yutaka Sakamura, Yusuke Yamada

       2015年07月

     概要を見る

    We express the action of six-dimensional supergravity in terms of
    four-dimensional N=1 superfields, focusing on the moduli dependence of the
    action. The gauge invariance of the action in the tensor-vector sector is
    realized in a quite nontrivial manner, and it determines the moduli dependence
    of the action. The resultant moduli dependence is intricate, especially on the
    shape modulus. Our result is reduced to the known superfield actions of
    six-dimensional global SUSY theories and of five-dimensional supergravity by
    replacing the moduli superfields with their background values and by performing
    the dimensional reduction, respectively.

  • Component action of nilpotent multiplet coupled to matter in 4 dimensional ${\cal N}=1$ supergravity

    Fuminori Hasegawa, Yusuke Yamada

       2015年07月

     概要を見る

    We construct the component action of the system including an ordinary matter
    and a nilpotent multiplet in global and local supersymmetric framework. The
    higher dimensional operators of not only Goldstino but also matter and
    gravitino fields are shown, which appear due to nonlinearly realized
    supersymmetry.

    DOI

    Scopus

    69
    被引用数
    (Scopus)
  • Massive vector multiplet inflation with Dirac-Born-Infeld type action

    Hiroyuki Abe, Yutaka Sakamura, Yusuke Yamada

       2015年05月

     概要を見る

    We investigate the inflation model with a massive vector multiplet in a case
    that the action of the vector multiplet is extended to the Dirac-Born-Infeld
    (DBI) type one. We show the massive DBI action in 4 dimensional ${\cal N}=1$
    supergravity, and find that the higher order corrections associated with the
    DBI-extension make the scalar potential flat with a simple choice of the matter
    couplings. We also discuss the DBI-extension of the new minimal Starobinsky
    model, and find that it is dual to a special class of the massive DBI action.

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Impacts of supersymmetric higher derivative terms on inflation models in supergravity

    Shuntaro Aoki, Yusuke Yamada

       2015年04月

     概要を見る

    We show the effects of supersymmetric higher derivative terms on inflation
    models in supergravity. The results show that such terms generically modify the
    effective kinetic coefficient of the inflaton during inflation if the cut off
    scale of the higher derivative operators is sufficiently small. In such a case,
    the $\eta$-problem in supergravity does not occur, and we find that the
    effective potential of the inflaton generically becomes a power type potential
    with a power smaller than two.

    DOI

    Scopus

    18
    被引用数
    (Scopus)
  • Matter coupled Dirac-Born-Infeld action in 4-dimensional N=1 conformal supergravity

    Hiroyuki Abe, Yutaka Sakamura, Yusuke Yamada

       2015年04月

     概要を見る

    We construct the Dirac-Born-Infeld action in the context of N=1 conformal
    supergravity and its possible extensions including matter couplings. We
    especially focus on the Volkov-Akulov constraint, which is important to avoid
    ghost modes from the higher derivative terms. In the case with matter
    couplings, we find the modified D-term potential.

    DOI

    Scopus

    10
    被引用数
    (Scopus)
  • N=1 superfield description of vector-tensor couplings in six dimensions

    Hiroyuki Abe, Yutaka Sakamura, Yusuke Yamada

       2015年01月

     概要を見る

    We express supersymmetric couplings among the vector and the tensor
    multiplets in six dimensions (6D) in terms of N=1 superfields. The superfield
    description is derived from the invariant action in the projective superspace.
    The obtained expression is consistent with the known superfield actions of 6D
    supersymmetric gauge theory and 5D Chern-Simons theory after the dimensional
    reduction. Our result provides a crutial clue to the N=1 superfield description
    of 6D supergravity.

    DOI

    Scopus

    8
    被引用数
    (Scopus)
  • Reheating processes after Starobinsky inflation in old-minimal supergravity

    Takahiro Terada, Yuki Watanabe, Yusuke Yamada, Jun'ichi Yokoyama

       2014年11月

     概要を見る

    We study reheating processes and its cosmological consequences in the
    Starobinsky model embedded in the old-minimal supergravity. First, we consider
    minimal coupling between the gravity and matter sectors in the higher curvature
    theory, and transform it to the equivalent standard supergravity coupled to
    additional matter superfields. We then discuss characteristic decay modes of
    the inflaton and the reheating temperature $T_{\rm R}$. Considering a simple
    model of supersymmetry breaking sector, we estimate gravitino abundance from
    inflaton decay, and obtain limits on the masses of gravitino and supersymmetry
    breaking field. We find $T_{\rm R}\simeq 1.0\times10^9$ GeV and the allowed
    range of gravitino mass as $10^4$ GeV $\lesssim m_{3/2} \lesssim 10^5$ GeV,
    assuming anomaly-induced decay into the gauge sector as the dominant decay
    channel.

    DOI

    Scopus

    36
    被引用数
    (Scopus)
  • Inflation in supergravity without Kahler potential

    Shuntaro Aoki, Yusuke Yamada

       2014年09月

     概要を見る

    We propose a new class of inflation models in supergravity with higher
    derivative terms. In those models, the K\"ahler potential does not contain the
    inflaton multiplet, but a supersymmetric derivative term does. In the models,
    inflation is effectively driven by a single scalar field with a standard
    kinetic term and a scalar potential. Remarkably, the so-called $\eta$ problem
    does not exist in our models.

    DOI

    Scopus

    21
    被引用数
    (Scopus)
  • Illustrating SUSY breaking effects on various inflation mechanisms

    Hiroyuki Abe, Shuntaro Aoki, Fuminori Hasegawa, Yusuke Yamada

       2014年08月

     概要を見る

    We consider the supersymmetry breaking effects on typical inflation models
    with different types of K\"ahler potential. The critical size of
    supersymmetry-breaking scale, above which the flatness of the inflaton
    potential is spoiled, drastically changes model by model. We present the
    universal description of such effects in terms of a field-dependent scaling
    factor by which gravity-mediated supersymmetry breaking terms are suppressed or
    enhanced, based on the conformal supergravity framework. Such a description
    would be useful when we estimate them in constructing supersymmetric models of
    particle cosmology.

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Natural realization of large extra dimension in 5D supersymmetric theory

    Yutaka Sakamura, Yusuke Yamada

       2014年01月

     概要を見る

    An exponentially large extra dimension can be naturally realized by the
    Casimir energy and the gaugino condensation in 5D supersymmetric theory. The
    model does not require any hierarchies among the 5D parameters. The key
    ingredient is an additional modulus other than the radion, which generically
    exists in 5D supergravity. SUSY is broken at the vacuum, which can be regarded
    as the Scherk-Schwarz SUSY breaking. We also analyze the mass spectrum and
    discuss some phenomenological aspects.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Impacts of non-geometric moduli on effective theory of 5D supergravity

    Yutaka Sakamura, Yusuke Yamada

       2013年07月

     概要を見る

    5D supergravity generically has non-geometric moduli other than the radion
    that belong to 5D vector multiplets. We summarize the impacts of such moduli on
    4D effective theory of 5D supergravity on S^1/Z_2. We mainly discuss the
    structure of the effective Kahler potential including the one-loop quantum
    corrections. As an illustrative example, we construct a model in which the size
    of the extra dimension is stabilized at an exponentially large value compared
    to the Planck length, which is similar to the LARGE volume scenario in string
    theory.

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Instant uplifted inflation: A solution for a tension between inflation and SUSY breaking scale

    Yusuke Yamada

       2012年11月

     概要を見る

    The Hubble parameter during the inflationary era must be smaller than the
    gravitino mass if the moduli are stabilized by the Kachru-Kallosh-Linde-Trivedi
    mechanism. This condition represents the difficulty to combine the low scale
    SUSY breaking and the high scale inflation. We propose a simple mechanism which
    can naturally separate the inflation scale from the SUSY breaking scale today.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • SUSY flavor structure of generic 5D supergravity models

    Hiroyuki Abe, Hajime Otsuka, Yutaka Sakamura, Yusuke Yamada

    European Physical Journal C   72 ( 5 ) 1 - 22  2011年11月

     概要を見る

    We perform a comprehensive and systematic analysis of the SUSY flavor
    structure of generic 5D supergravity models on $S^1/Z_2$ with multiple
    $Z_2$-odd vector multiplets that generate multiple moduli. The SUSY flavor
    problem can be avoided due to contact terms in the 4D effective K\"ahler
    potential peculiar to the multi-moduli case. A detailed phenomenological
    analysis is provided based on an illustrative model.

    DOI

    Scopus

    12
    被引用数
    (Scopus)

▼全件表示

Misc

  • QFT approach to dressed particle processes in preheating and non-perturbative mechanism in kinematically-forbidden regime

    Hidetoshi Taya, Yusuke Yamada

       2022年07月

     概要を見る

    We provide a quantum-field theoretic formulation of dressed particle dynamics
    that systematically include particle production and scattering/decay processes
    in the preheating era. Our approach is based on the so-called perturbation
    theory in the Furry picture, in which coherent background fields (i.e.,
    inflaton and the expanding Universe) are treated non-perturbatively whereas
    interactions between dressed particles are taken into account perturbatively.
    As application, we consider the instant preheating mechanism and compute the
    number of produced particles explicitly, assuming that the coherent fields are
    adiabatic. We find a novel non-perturbative particle-production mechanism,
    which is kinematically forbidden within the conventional perturbative
    calculation and produces particles exponentially efficiently than the
    perturbative one does.