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In this work, we explore the possibility that Early Dark Energy (EDE) is dynamical in nature and study its effect on cosmological observables. We introduce a parameterization of the equation of state allowing for an equation of state $w$ differing considerably from cosmological constant (cc, $w={-1}$) and vary both the initial $w_i$ as well final $w_f$ equation of state of the EDE fluid. This idea is motivated by the fact that in many models of EDE, the scalar field may have some kinetic energy when it starts to behave like EDE before the CMB decoupling. We find that the present data have a mild preference for non-cc early dark energy $( w_i= -0.78)$ using Planck+BAO+Pantheon+S$H_0$ES data sets, leading to $\Delta \chi^2_{\rm min}$ improvement of -2.5 at the expense of one more parameter. However, $w_i$ is only weakly constrained, with $w_i < -0.56$ at $1\sigma$. We argue that allowing for $w_i\neq -1$ can play a role in decreasing the $\sigma_8$ parameter. Yet, in practice the decrease is only $\sim0.4\sigma$ and $\sigma_8$ is still larger than weak lensing measurements. We conclude that while promising, a dynamical EDE cannot resolve both $H_0$ and $\sigma_8$ tensions simultaneously., Comment: 8 figures, Comments are most welcome

We present small-scale structure constraints on sterile dark matter produced from a heavy mediator particle, inspired by models of moduli decay. Dark matter particles produced through this mechanism can contribute to the entire dark matter energy density but the particles have a non-thermal phase-space distribution; however, we show that the resulting linear matter power spectra can be mapped to effective thermal-relic warm dark matter models. This production mechanism is therefore subject to warm dark matter constraints from small-scale structure as probed by ultra-faint dwarf galaxy abundances and strong gravitational lensing flux ratio statistics. We use the correspondence to thermal-relic models to derive a lower bound on the non-thermal particle mass of $107\ \mathrm{keV}$, at $95\%$ confidence. These are the first and most stringent constraints derived on sterile dark matter produced via the heavy mediator decay scenario we consider., Comment: Comments are most welcome

Cosmologies with Light Massive Relics (LiMRs) as a subdominant component of the dark sector are well-motivated from a particle physics perspective, and can also have implications for the $\sigma_8$ tension between early and late time probes of matter clustering. The effects of LiMRs on the Cosmic Microwave Background (CMB) and structure formation on large (linear) scales have been investigated extensively. In this paper, we initiate a systematic study of the effects of LiMRs on smaller, nonlinear scales using cosmological $N$-body simulations; focusing on quantities relevant for photometric galaxy surveys. For most of our study, we use a particular model of nonthermal LiMRs but the methods developed easily generalize to a large class of models of LiMRs -- we explicitly demonstrate this by considering the Dodelson-Widrow form of the velocity distribution. We find that, in general, the effects of LiMR on small scales are distinct from those of a $\Lambda$CDM universe, even when the value of $\sigma_8$ is matched between the models. We show that weak lensing measurements around massive clusters, between $\sim 0.1 h^{-1}$Mpc and $\sim 10 h^{-1}$Mpc, should have sufficient signal-to-noise in future surveys to distinguish between $\Lambda$CDM and LiMR models that are tuned to fit both CMB data and large (linear) scale structure data at late times. Furthermore, we find that different LiMR cosmologies which are indistinguishable by conventional linear probes can be distinguished by these probes if their velocity distributions are sufficiently different. LiMR models can, therefore, be best tested and constrained by jointly analyzing data from CMB and late-time structure formation on both large \textit{and} small scales., Comment: 6 figures

Recently there has been reports of finding a lower bound on the neutrino mass parameter ($\Sigma m_\nu$) when using ACT and SPTpol data however these bounds on the $\Sigma m_\nu$ are still weaker for most case around at 1 $\sigma$ level. In this context, here in this work, we study the consequences of using an enlarged four parameter dynamical dark energy equation of state on neutrino mass parameter as well as on the Hubble and S8 tensions. The four parameter dark energy equation of state incorporates a generic non-linear monotonic evolution of the dark energy equation of state, where the four parameters are the early and the present value of the equation of state, the transition scale factor and the sharpness of the transition. We report that with lensing-marginalized Planck + BAO + Pantheon and prior on absolute magnitude $M_B$ and KIDS/Viking $S_8$ prior, the model favours a non-zero value for the neutrino mass parameter at the most at $\sim 1 \sigma$ level ($\Sigma m_\nu = 0.1847_{-0.165}^{+0.0698}$ eV). In this case this model also brings down the Hubble tension to $\sim 2.5 \sigma$ level and the S8 tension to $\sim$ 1.5 $\sigma$ level. This model also provide a tighter constraints on the value of the dark energy equation of state at present epoch $w_0$ ($w_0 = -0.9901_{-0.0766}^{+0.0561}$) in comparison to the CPL like parameterization., Comment: accepted for Astrophysical Journal,more figures added

The $\Lambda$CDM prediction of $S_8\equiv\sigma_8(\Omega_m/0.3)^{0.5}$ -- where $\sigma_8$ is the root mean square of matter fluctuations on a 8 $h^{-1}$Mpc scale -- once calibrated on Planck CMB data is $2-3\sigma$ lower than its direct estimate by a number of weak lensing surveys. In this paper, we explore the possibility that the '$S_8$-tension' is due to a non-thermal hot dark matter (HDM) fractional contribution to the universe energy density leading to a power suppression at small-scales in the matter power spectrum. Any HDM models can be characterized by its effective mass $ m_{sp}^{\rm eff}$ and its contribution to the relativistic degrees of freedom at CMB decoupling $\Delta N_{\rm eff}$. Taking the specific example of a sterile particle produced from the decay of the inflaton during a matter dominated era, we find that from Planck only the tension can be reduced below $2\sigma$, but Planck does not favor a non-zero ${m_{sp}^{\rm eff},\Delta N_{\rm eff}}$. In combination with a measurement of $S_8$ from KIDS1000+BOSS+2dfLenS, the $S_8$-tension would hint at the existence of a particle of mass $ m_{sp}^{\rm eff} \simeq 0.67_{-0.48}^{+0.26}$ ${\rm eV}$ with a contribution to $\Delta N_{\rm eff} \simeq0.06\pm0.05$. However, Pantheon and BOSS BAO/$f\sigma_8$ data restricts the particle mass to $m_{sp}^{\rm eff} \simeq 0.48_{-0.36}^{+0.17}$ and contribution to $\Delta N_{\rm eff} \simeq 0.046_{-0.031}^{+0.004}$. We discuss implications of our results for other canonical non-thermal HDM models -- the Dodelson-Widrow model and a thermal sterile particle with a different temperature in the hidden sector. We report competitive results on such hidden sector temperature which might have interesting implications for particle physics model building, in particular connecting the $S_8$-tension to the longstanding short baseline oscillation anomaly., Comment: accepted Physical Review D, new figures, references and discussion added conclusion is same