We consider a cosmological lepton asymmetry in the form of neutrinos and impose new expected sensitivities on such asymmetry through the degeneracy parameter ($\xi_\nu$) by using some future CMB experiment configurations, such as CORE and CMB-S4. Taking the default scenario with three neutrino states, we find $\xi_\nu =0.05±0.10(±0.04)$, from CORE (CMB-S4) at 95 per cent CL, respectively....
We present a detailed investigation of a sub-dominant oscillating scalar field ('early dark energy', EDE) in the context of resolving the Hubble tension. Consistent with earlier work, but without relying on fluid approximations, we find that a scalar field frozen due to Hubble friction until log10($z_c$)∼3.5, reaching ρ$_{\rm EDE}$($z_c$)/ρ$_{\rm tot}$∼10%, and diluting faster than matter...
Dark matter problem is a key problem in astrophysics. Recent gamma-ray and anti-proton detections suggest that dark matter annihilating via b quark channel can explain the Galactic center gamma-ray excess and the anti-proton excess simultaneously. Besides, recent studies show that radio data can also give stringent constraints for dark matter. Based on our recent studies using the radio...
Despite their incredible precision, both concluded and upcoming CMB missions (such as Planck, CMB-S4, or LiteBIRD) still face several intrinsic limitations that can only be overcome with the help of complementary probes. One particularly interesting avenue to extract more information from the CMB is given by its spectral distortions (SDs). Since these distortions are created whenever the...
In this work we estimated the cosmological constant in a pioneering approach by using galactic superclusters in the layout of $f(R,T)$ gravity. We set $f(R,T) = R + 2\lambda T$ where $\lambda$ is the model parameter. We report that appropriate values of $\lambda$ generate cosmological constant ($\Lambda$) values in harmony with observational value of $1.1056\times10^{-52}m^{-2}$. We also...
In a variety of theories, DM interacts with gauge bosons or scalars that induce long-range interactions because of repeated soft exchanges. Remarkably, the inclusion of bound-state effects for DM annihilation has been recently shown to have a large impact on the relic density and, therefore, on the parameters of a given model to be compatible with observations. At the same time, it is...
We consider scalar field models of dark matter, with a mass in the range 10^{-21} << m << 10^{-3} eV. In the nonrelativistic regime, derivative or potential self-interactions can give rise to an effective pressure that builds equilibrium configurations (solitons) in galactic halos. We extend the analysis to the relativistic regime, down to the horizon of the supermassive galactic Black Hole...
Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of galaxies. In calculations of spherically symmetric collapse, a Lagrangian relativistic hydrodynamical code is used to...
The light mediator scenario of self-interacting dark matter is strongly constrained in many ways. After summarizing the various constraints, we discuss minimal options and models which allow to nevertheless satisfy all these constraints.
Generalized coupling theories are characterized by a nontrivial coupling between the gravitational metric and matter, which is mediated by an auxiliary rank-2 tensor. The actions generating the field equations are constructed so that these theories are equivalent to general relativity in a vacuum, and only differ from Einstein's theory within a matter distribution. This talk will focus on one...
If the length scale of possible extra dimensions is large enough, the effective Planck scale is lowered such that microscopic black holes could be produced in collisions of high-energy particles, which opens up a plethora of novel phenomena in terrestrial detectors and in the early Universe. Microscopic black holes from high-energy cosmic neutrino-nucleon collisions are characterized by unique...
This talk will be mainly based on the paper; R. Erdem and K. Gultekin. JCAP 10 (2019) 061. By considering dynamics of a scalar Bose-Einstein condensation at microscopic level, we study the initial phase of formation of condensation in cosmology. To this end, first we introduce an effective Minkowski space formulation that enables considering only the effect of particle physics processes,...
We show that Dark Matter consisting of ultralight bosons in a Bose-Einstein condensate induces, via its quantum potential, a small positive cosmological constant which is close to the observed value. This explains why the densities of Dark Matter and Dark Energy are approximately equal.
[NOTE ADDED MC 2020.03.03 if abstract is selected, talk scheduled for 27, 28 or 29 April (i.e. Monday,...
If we consider sterile neutrino with a O(keV) mass as Warm Dark Matter candidates, produced in the early universe through admixtures with the active neutrinos, via the Dodelson-Widrow or the Shi-Fuller mechanisms, strong constraints on the active-sterile mixing angle are imposed by the observations in the X-ray band and the measurements of the total DM abundance. These constraints, that in a...
The properties of universes are explored that are entirely in the interior of black holes in another universe, a `mother universe'. It is argued that these models offer a paradigm that may shed a new light on old cosmological problems. The geometry of such a universe is discussed including how it would appear to the observer. The Hubble parameter is direction dependent, but it is argued that...
We investigate the correlation between the distribution of galaxies and the predicted gravitational wave background of astrophysical origin. We show that the average contribution to the background as a function of redshift can be easily constrained by cross-correlating with galaxy catalogs at different redshifts. Furthermore, the interpretation of this signal allows us to address the...
Solutions of string theory with a four-dimensional de Sitter space-time could serve as an interesting starting point to build cosmological models of the early universe, or the present one. Obtaining such solutions in a well-controlled manner is however notoriously difficult. This has recently led to various conjectures, in the context of the swampland program, that strongly constrain the...
We revisit the scalar singlet dark matter (DM) scenario with a pair of dark lepton partners which form a vector-like Dirac fermionic doublet. The extra doublet couples with the SM leptonic doublet and the scalar singet via a non-SM-like Yukawa structure. As a result, (1) since the extra fermionic states interact with other dark sector particles as well as the SM via gauge and Yukawa...
Despite its remarkable success, the standard LCDM paradigm has been challenged lately by significant tensions between different datasets. This has boosted interest in non-minimal dark sectors, which are theoretically well-motivated and inspire new search strategies for DM. With this in mind, we have developed a new and efficient version of the Boltzmann code CLASS that allows for one DM...
Early Dark Energy (EDE) contributing a fraction f_EDE(z_c) ∼ 10% of the energy density of the universe around z_c = 3500 and diluting as or faster than radiation afterwards, can provide a simple resolution to the Hubble tension, the ∼ 5σ discrepancy – in the ΛCDM context – between the H0 value derived from early- and late-universe observations. However, the inclusion of Large-Scale Structure...
Recent weak lensing surveys have revealed that the direct measurement of the parameter combination S8 = σ8 (Ωm/0.3)^0.5-- measuring the amplitude of matter fluctuations on 8 Mpc/h scales -- is ∼3σ discrepant with the value reconstructed from cosmic microwave background (CMB) data assuming the ΛCDM model. In this talk, I discuss that it is possible to resolve the tension if dark matter (DM)...
Dark matter (DM) in cosmic structures is expected to produce signals originating from its particle physics nature, among which the electromagnetic emission represents a relevant opportunity. One of the major candidates for DM are weak-scale particles, however no convincing signal of them has been observed so far. For this reason, alternative candidates are getting increasing attention, notably...
Thermal freeze-in is a simple scenario of dark matter production that can however be very difficult to probe. We discuss a decaying dark matter setup in which the feeble coupling required to reproduce the observed relic abundance gives rise to transitions between dark matter components, resulting in gamma ray spectral features.
In the present work, we have presented and analyzed the cosmological models of the universe with an anisotropic variable parameter. We have set up the ?field equations with the space time in the form of Bianchi I metric with an f(R;T) gravity. The functional form for the f(R;T) gravity assumed to be f(R;T) = R + 2f(T), where R and T respectively the Ricci scalar and trace of energy momentum...
Particle production by oscillating curvature in $R+R^2$ cosmology is considered. It is shown that the cosmological density of massive stable relics may be close to the observed density of dark matter. The proper range of mass values depends on the channel of the scalaron decay. In particular it opens the window for heavy supersymmetric particles to be viable dark matter constituents.
The large-scale structure growth index γ provides a consistency test of the standard cosmology and is a potential indicator of modified gravity. We investigate the constraints on γ from next-generation spectroscopic surveys (like SKA, Euclid and DESI), and possible improvements from combining these using a multi-tracer technique. Using the angular power spectrum, which is observed in redshift...
We derive the modified Friedmann equations based on non-extensive Tsallis thermodynamics. This model admits an accelerated expansion for the universe filled by ordinary matter and without needing dark energy. The age problem can also be alleviated in this model.
Extra dimensions (ED) have been used as attempts to explain several phenomena in particle physics, such as the hierarchy and flavor problems. The interaction between new mediators in the bulk (vector, scalar of fermion fields) and the Standard Model (SM) particles can be naturally suppressed if one employs a single, flat ED. In this setup, the SM fields are localized in a finite width ‘fat’...
Degenerate scalar-tensor theories of gravity extend general relativity by a single degree of freedom, despite their equations of motion being higher than second order, a virtue made possible by the existence of an additional constraint that removes the would-be ghost. This constraint can however be obstructed by matter fields, even when minimally coupled to the metric. In this talk I will...
We propose a 1/N expansion of Starobinsky and Yokoyama’s effective stochastic approach for light quantum fields on superhorizon scales in de Sitter spacetime. We explicitly compute the spectrum and the eigenfunctions of the Fokker-Planck operator for a O(N)-symmetric theory with quartic selfinteraction at leading and next-to-leading orders in this expansion. We obtain simple analytical...
We are investigating if the double copy structure as product of scattering amplitudes
of gauge theories applies to cosmological correlators computed, in a class of theories for
inflation, by the operatorial version of the In-In formalism of Schwinger-Keldysh. We
consider tree level momentum-space correlators involving primordial gravitational waves
with different polarizations and the...
