arXiv subjects

Stharporn Sapa

Publications and source records attributed to Stharporn Sapa.

4 recordsLinked to original sources

arXiv2026

Cluster number counts in dark energy model with energy and momentum coupling to dark matter

The influences on the cluster number counts from the coupling between dark energy and dark matter with momentum transfer are investigated. We find that the extrapolated linear density contrast computed from the spherical collapse model is suppressed when the strength of momentum transfer is increased. Using the Sheth-Tormen mass function, the cluster number counts are computed. The minimum mass limit in the mass integration for each redshift bin is determined by matching the predicted number counts from the $Λ$CDM model with the result from eROSITA surveys. We find that the number of clusters is maximal at a higher redshift bin, and the number of clusters in a maximum redshift bin is enhanced when the strength of momentum and energy transfers increases due to the reduction of extrapolated linear density contrast. Setting the parameters of the dark energy model with momentum coupling according to the observational constraints in \cite{bestfit}, the predicted number counts from the coupled dark energy is larger than the result from eROSITA surveys. The statistical analysis yields a $p$-value of 0.189 for the proposed model relative to $Λ$CDM. Consequently, there is no statistically significant evidence of an improved fit over the standard $Λ$CDM framework based on the eROSITA cluster number counts.

astro-ph.CO↗

arXiv2022

Coupled dark energy model inspired from general conformal transformation

We study the coupled dark energy model constructed from the general conformal transformation in which the coefficient of the conformal transformation depends on both the scalar field and its kinetic term. Under this conformal transformation, the action for subclass of Degenerate Higher-Order Scalar-Tensor (DHOST) theories is related to the Einstein-Hilbert action. The evolution of the background universe has the scaling fixed point which corresponds to acceleration of the universe at late time. For the choices of parameters which make the late-time scaling point stable, the fixed point corresponding to $ϕ$-matter-dominated-era ($ϕ$MDE) is a saddle point, and the universe can evolve from radiation dominated epoch through $ϕ$MDE before reaching the scaling point at late time with the cosmological parameters which satisfy the observational bound. During the $ϕ$MDE, the effective equation of state parameter is slightly positive, so that one of possible mechanisms for alleviating the $H_0$ tension can be achieved. In this coupled dark energy model, the effective gravitational coupling for dark matter perturbations on small scales can be smaller than that in the $Λ$CDM model. Therefore a growth rate of the dark matter perturbations is suppressed compare with the $Λ$CDM model, which implies that the $σ_8$ tension could be alleviated.

gr-qc↗

arXiv2018

Spherical collapse and cluster number counts in dark energy models disformally coupled to dark matter

We investigate the effects of a disformal coupling between dark energy and dark matter in the predictions of the spherical collapse and its signatures in galaxy cluster number counts. We find that the disformal coupling has no significant effects on spherical collapse at high redshifts, and in particular during matter domination epoch. However, at lower redshifts, the extrapolated linear density contrast at collapse close to redshift $z \lesssim 1$ and overdensity at virialization can be strongly suppressed by a disformal coupling between dark energy and dark matter. We also find that disformal coupling can have different imprints on cluster number counts compared with conformal coupling, such that the disformal coupling can strongly suppress the predicted number of clusters per redshift interval at $z > 0.1$ while enhance the number of cluster at $z < 0.05$. Using the specifications of eROSITA survey, we find that the disformal coupling between dark energy and dark matter can be tightly constrained by cluster number counts.

astro-ph.CO↗

arXiv2017

Dynamics of the universe with disformal coupling between the dark sectors

We use the dynamical analysis to study the evolution of the universe at late time for the model in which the interaction between dark energy and dark matter is inspired by disformal transformation. We extend the analysis in the existing literature by supposing that the disformal coefficient depends both on the scalar field and its kinetic terms. We find that the dependence of the disformal coefficient on the kinetic term of scalar field leads to two classes of the scaling fixed points that can describe the acceleration of the universe at late time. The first class exists only for the case where the disformal coefficient depends on the kinetic terms. The fixed points in this class are saddle points unless the slope of the conformal coefficient is sufficiently large. The second class can be viewed as the generalization of the fixed points studied in the literature. According to the stability analysis of these fixed points, we find that the stable fixed point can take two different physically relevant values for the same value of the parameters of the model. These different values of the fixed points can be reached for different initial conditions for the equation of state parameter of dark energy. We also discuss the situations in which this feature disappears.

gr-qc↗