Updated on 2022/08/17


Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Assistant Professor(without tenure)


  • 2014.09

    Waseda University   Graduate School of Advanced Science and Engineering  


Research Areas

  • Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

Research Interests

  • Gravity

  • Cosmology


  • Resolving Hubble Tension with Quintom Dark Energy Model

    Sirachak Panpanich, Piyabut Burikham, Supakchai Ponglertsakul, Lunchakorn Tannukij


     View Summary

    Recent low-redshift observations give value of the present-time Hubble
    parameter $H_{0}\simeq 74~\rm{km s}^{-1}\rm{Mpc}^{-1}$, roughly 10\% higher
    than the predicted value $H_{0}=67.4~\rm{km s}^{-1}\rm{Mpc}^{-1}$ from Planck's
    observations of the Cosmic Microwave Background radiation~(CMB) and the
    $\Lambda$CDM model. Phenomenologically, we show that by adding an extra
    component X with negative density in the Friedmann equation, it can relieve the
    Hubble tension without changing the Planck's constraint on the matter and dark
    energy densities. For the extra negative density to be sufficiently small, its
    equation-of-state parameter must satisfy $1/3\leq w_{X}\leq1$. We propose a
    quintom model of two scalar fields that realizes this condition and potentially
    alleviate the Hubble tension. One scalar field acts as a quintessence while
    another "phantom" scalar conformally couples to matter in such a way that
    viable cosmological scenario can be achieved. The model depends only on two
    parameters, $\lambda_{\phi}$ and $\delta$ which represent rolling tendency of
    the self-interacting potential of the quintessence and the strength of
    conformal phantom-matter coupling respectively. The toy quintom model with
    $H_{0}=73.4~\rm{km s}^{-1}\rm{Mpc}^{-1}$~(Quintom I) gives good Supernovae-Ia
    luminosity fits, decent $r_{\rm BAO}$ fit, but slightly small acoustic
    multipole $\ell_{A}=285.54$. Full parameter scan reveals that quintom model
    provide better model than the $\Lambda$CDM model in certain region of the
    parameter space, $0.02<\delta<0.10, \Omega_{m}^{(0)}<0.31$, while significantly
    relieving Hubble tension even though not completely resolving it. A benchmark
    quintom model, Quintom II, is presented as an example.

  • Particle motions and Gravitational Lensing in de Rham-Gabadadze-Tolley Massive Gravity Theory

    Sirachak Panpanich, Supakchai Ponglertsakul, Lunchakorn Tannukij


     View Summary

    We investigate gravitational lensing and particle motions around
    non-asymptotically flat black hole spacetime in non-linear, ghost-free massive
    gravity theory, called de Rham-Gabadadze-Tolley (dRGT) massive gravity.
    Deflection angle formulae are derived in terms of perihelion parameter. The
    deflection angle can be positive, zero or even negative with various perihelion
    distance. The negative angle reveals repulsive behaviour of gravity from a
    linear term $\gamma$ in the dRGT black hole solution. We also find an
    analytically approximated formula of deflection angle in two regimes: large and
    small $\gamma$ term regimes which are shown to be consistent with direct
    numerical integration. Null and timelike geodesic motions on equatorial plane
    are explored. Particle trajectories around the dRGT black hole are plotted and
    discussed in details.


  • Cosmological Dynamics and Double Screening of DBI Galileon Gravity

    Sirachak Panpanich, Supakchai Ponglertsakul, Kei-ichi Maeda


     View Summary

    We investigate cosmological dynamics and screening mechanism of the
    Dirac-Born-Infeld (DBI) Galileon model. The model has been divided into two
    regimes, one has positive signs in front of scalar field kinetic terms
    so-called the DBI galileon, another one has negative signs and it is dubbed as
    the DBIonic galileon. We find de Sitter solution and evolution of the Universe
    starting from radiation dominated era to late-time accelerated expansion in the
    DBI galileon model without the presence of potential term. In one of the
    attractors, the ghost and Laplacian instabilities vanishes for the whole
    evolution. We find mixing of screening mechanisms between the Vainshtein
    mechanism and the DBIonic screening mechanism in the DBIonic galileon model, in
    which a scale changing between these two mechanisms depends on a mass of a


  • Fitting rotation curve of galaxies by de Rham-Gabadadze-Tolley massive gravity

    Sirachak Panpanich, Piyabut Burikham


     View Summary

    We investigate effects of massive graviton on the rotation curves of the
    Milky Way, spiral galaxies and Low Surface Brightness~(LSB) galaxies. Using a
    simple de Rham, Gabadadze, and Tolley (dRGT) massive gravity model, we find
    static spherically symmetric metric and a modified Tolman-Oppenheimer-Volkoff
    (TOV) equation. The dRGT nonlinear graviton interactions generate density and
    pressures which behave like a dark energy that can mimic the gravitational
    effects of a dark matter halo. We found that rotation curves of most galaxies
    can be fitted well by a single constant-gravity parameter $\gamma \sim
    m_{g}^{2}C \sim 10^{-28}~{\rm m^{-1 } }$ corresponding to the graviton mass in
    the range $m_g \sim 10^{-21}-10^{-30} {\rm eV}$ depending on the choice of the
    fiducial metric parameter $C\sim 1-10^{18}~\text{m}$. Fitting rotation curve of
    the Milky Way puts strong constraint on the Yukawa-type coupling of the massive
    graviton exchange as a result of the shell effects.


  • Cosmological Dynamics of D-BIonic and DBI Scalar Field and Coincidence Problem of Dark Energy

    Sirachak Panpanich, Kei-ichi Maeda, Shuntaro Mizuno


     View Summary

    We study the cosmological dynamics of D-BIonic and DBI scalar field, which is
    coupled to matter fluid. For the exponential potential and the exponential
    couplings, we find a new analytic scaling solution yielding the accelerated
    expansion of the Universe. Since it is shown to be an attractor for some range
    of the coupling parameters, the density parameter of matter fluid can be the
    observed value, as in the coupled quintessence with a canonical scalar field.
    Contrary to the usual coupled quintessence, where the value of matter couple
    giving observed density parameter is too large to satisfy observational
    constraint from CMB, we show that the D-BIonic theory can give similar solution
    with much smaller value of matter coupling. As a result, together with the fact
    that the D-BIonic theory has a screening mechanism, the D-BIonic theory can
    solve the so-called coincidence problem as well as the dark energy problem.


  • Effects of Chameleon Scalar Field on Rotation Curves of the Galaxies

    Piyabut Burikham, Sirachak Panpanich


     View Summary

    We investigate the effects of chameleon scalar field to the effective density
    and pressure of a dark matter halo. The pressure is generated from the
    chameleonic fifth force on the matter. We demonstrate that the thick-shell
    non-singular boundary condition which forbids singular point leads to extremely
    stringent constraint on the matter-chameleon coupling when applied to galaxy.
    We argue that chameleon profile with central singularity is more likely to
    develop in general physical situation. The chameleonic fifth force from the
    chameleon profile with central singularity experienced by the dark matter could
    significantly modify the rotation curve of galaxies. The chameleonic fifth
    force could generate steeper cusp to the rotation curves in any dark matter
    profiles starting from the Navarro-Frenk-White (NFW) to the pseudo-isothermal
    (ISO) profile. Upper limits on the coupling constant between the chameleon and
    the dark matter are estimated from observational data of the late-type
    Low-Surface-Brightness galaxies (LSB). It is in the order of $\beta < 10^{-3}$.


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Specific Research

  • Dark Energy Model Satisfying the Solar System Observations

    2021   Kei-ichi MAEDA

     View Summary

    We study the modified gravity theory, names cuscuta-galileon gravity to explain the accelerated expansion of the universe by using a nondynamical scalar field. We find that the model can provide the sequence of the thermal history of the universe correctly, in the same time the gravitational coupling is modified from the Newtonian gravitational constant. Interestingly, the new gravitational coupling depends on time, then it leads to a changing on the Hubble parameter. As a result, the present value of the Hubble parameter in our model increases from the standard model of cosmology, the Lambda-Cold-Dark-Matter model, about 10%, then it might be a tendency to solve one of the recent problems in cosmology, so-called the Hubble tension problem. Observations in universe such as Big-Bang-Nucleosysthesis and Lunar-Laser-Ranging also provide constraints on parameters of the model, however the model can satisfy these observations. The above results have been done under some conditions, namely we assume an exponential form of potential for the scalar field. Thus other forms of potential may give other possibilities and results. We also improve the model by adding a small negative vacuum energy, it leads to a smaller of the present value of the Hubble parameter which satisfies the latest observations on Super Novae Type IA.

  • Cosmological dynamics and screening mechanisms of modified gravity theories

    2020   MAEDA Kei-ichi

     View Summary

    We study cosmology dynamics of the cuscuta-galileon gravity. This model has only two gravitational degrees of freedom as the General Relativity, thus it is satisfied observations in the solar system scale. We use dynamical system approach to find behavior under cosmological background. We found that the cuscuta-galileon model without a potential term cannot provide the thermal history of the universe correctly. After adding a potential term we successfully find radiation dominated, matter dominated, and dark energy dominated eras. By studying stabilities of the dynamical system we found that if we start from the radiation dominated era, it will follow by matter dominated and dark energy dominated eras respectively which corresponds to the thermal history of the universe. Therefore the model can be one of the candidates for the dark energy to explain the accelerated expansion of the universe. However, the amount of dark energy in the matter dominated and the radiation dominated eras is large comparing to the cosmological constant. Thus, some observations such as the Cosmic Microwave Background, the cuscuta-galileon gravity may not satisfy. Moreover, in the perturbations level we found that there is an instability in the model which arises from negative sound speed squared.



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