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We investigate two-field inflationary models in which scalar cosmological pertubations are generated via a spectator field nonminimally coupled to gravity, with the particular emphasis on curvaton scenarios. The principal advantage of these models is in the possibility to tune the spectator spectral index via the nonminimal coupling. Our models naturally yield red spectrum of the adiabatic perturbation demanded by observations. We study how the nonminimal coupling affects the spectrum of the curvature perturbation generated in the curvaton scenarios. In particular we find that for small, negative nonminimal couplings the spectral index gets a contribution that is negative and linear in the nonminimal coupling. Since in this way the curvature spectrum becomes redder, some of curvaton scenarios can be saved, which would otherwise be ruled out. In the power law inflation we find that a large nonminimal coupling is excluded since it gives the principal slow roll parameter that is of the order of unity. Finally, we point out that nonminimal coupling can affect the postinflationary growth of the spectator perturbation, and in this way the effectiveness of the curvaton mechanism.
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We consider a simple abelian vector dark matter (DM) model, where {it only} the DM $(widetilde{X}_mu)$ couples non-minimally to the scalar curvature $(widetilde{R})$ of the background spacetime via an operator of the form $sim widetilde{X}_mu,widetilde{X}^mu,widetilde{R}$. By considering the standard freeze-out scenario, we show, it is possible to probe such a non-minimally coupled DM in direct detection experiments for a coupling strength $xisimmathcal{O}left(10^{30}right)$ and DM mass $m_Xlesssim 55$ TeV, satisfying Planck observed relic abundance and perturbative unitarity. We also discuss DM production via freeze-in, governed by the non-minimal coupling, that requires $xilesssim 10^5$ to produce the observed DM abundance over a large range of DM mass depending on the choice of the reheating temperature. We further show, even in the absence of the non-minimal coupling, it is possible to produce the whole observed DM abundance via 2-to-2 scattering of the bath particles mediated by massless gravitons.
We consider a model where a light scalar field (with mass $lesssim 30, {rm eV}$), conjectured to be dark matter, has a non-minimal coupling to gravity. In the non-relativistic limit, this new coupling introduces a self-interaction term in the scalar-field equation of motion, and modifies the source term for the gravitational field. Moreover, in the small-coupling limit justified by the observed dark-matter density, the system further reduces to the Gross-Pitaevskii-Poisson equations, which remarkably also arise from a self-gravitating and self-interacting Bose-Einstein condensate system. We derive predictions of our model on linear and non-linear structure formation by exploiting this unexpected connection.
We investigate self-gravitating equilibria of halos constituted by dark matter (DM) non-minimally coupled to gravity. In particular, we consider a theoretically motivated non-minimal coupling which may arise when the averaging/coherence length $L$ associated to the fluid description of the DM collective behavior is comparable to the local curvature scale. In the Newtonian limit, such a non-minimal coupling amounts to a modification of the Poisson equation by a term $L^2, abla^2rho$ proportional to the Laplacian of the DM density $rho$ itself. We further adopt a general power-law equation of state $ppropto rho^{Gamma}, r^alpha$ relating the DM dynamical pressure $p$ to density $rho$ and radius $r$, as expected by phase-space density stratification during the gravitational assembly of halos in a cosmological context. We confirm previous findings that, in absence of the non-minimal coupling, the resulting density $rho(r)$ features a steep central cusp and an overall shape mirroring the outcomes of $N-$body simulations in the standard $Lambda$CDM cosmology, as described by the classic NFW or Einasto profiles. Most importantly, we find that the non-minimal coupling causes the density distribution to develop an inner core and a shape closely following, out to several core scale radii, the Burkert profile. In fact, we highlight that the resulting mass distributions can fit, with an accuracy comparable to the Burkerts one, the co-added rotation curves of dwarf, DM-dominated galaxies. Finally, we show that non-minimally coupled DM halos are consistent with the observed scaling relation between the core radius $r_0$ and core density $rho_0$, in terms of an universal core surface density $rho_0times r_0$ among different galaxies.
In a logamediate inflationary universe model we introduce the curvaton field in order to bring this inflationary model to an end. In this approach we determine the reheating temperature. We also outline some interesting constraints on the parameters that describe our models. Thus, we give the parameter space in this scenario.
Inspired by cite{Jiang:2018uce}, we propose a similar curvaton mechanism whose realization occurs in preheating process, in which the effective mass is running (its potential consists of coupling part and exponential part whose contribution is subdominant comparing to the coupling part). The production of curvaton contains the cases of narrow resonance and broad resonances whose criteria comes via the spectral index of curvaton. Since the inflationary potential is chaotic inflation (quadratic potential), it could smoothly transit into the preheating process. Once the entropy perturbation transferred into curvature perturbation, we will use $delta N$ formalism to investigate its validity. By neglecting the contribution of exponential potential of curvaton, we calculate power spectrum $P_zeta$ and non linear Non-Gaussian parameter $f_{NL}$. Our calculation analytically shows that these two observables are independent of potential of inflaton. Finally, as the curvaton almost decay (inflaton field vanishes), the exponential potential will be approaching a constant of order of cosmological constant, which may play a role of dark energy.
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