We consider light dark matter candidates originated from the evaporation of Schwarzschild primordial black holes, with masses in the range $10^{-5}-10^9$ g. These candidates are beyond Standard Model particles with negligible couplings to the other particles, so that they interact only gravitationally. Belonging to the category of warm dark matter, they nevertheless spoil structure formation, with a softer impact for increasing values of the candidate spin. Requiring such candidates to fully account for the observed dark matter, we find that the scenario of black hole domination is ruled out for all spin values up to 2. For the scenario of radiation domination, we derive upper limits on the parameter $β$ (the primordial black hole energy density at formation over the radiation one), which are less stringent the higher the candidate spin is.
We study scalar field fluctuations of the inflaton field in an early inflationary universe on an effective 4D Schwarzschild-de Sitter (SdS) metric, which is obtained after make a planar coordinate transformation on a 5D Ricci-flat Schwarzschild-de Sitter (SdS) static metric. We obtain the important result that the spectrum of fluctuations at zeroth order is independent of the scalar field mass $M$ on Schwarzschild scales, while on cosmological scales it exhibits a mass dependence. However, in the first-order expansion, the spectrum depends of the inflaton mass and the amplitude is linear with …
Primordial Black Holes (PBHs) serve as a unique probe to the physics of the early Universe, particularly inflation. In light of this, we study the formation of PBHs by the collapse of overdense perturbations generated during a model of warm inflation. For our model, we find that the primordial curvature power spectrum is red-tilted (spectral index $n_s<1$) at the large scale (small $k$) and is consistent with the $n_s-r$ values allowed from the CMB observations. Along with that, it has a blue-tilt ($n_s>1$) for the small PBH scales (large $k$), with a sufficiently large amplitude of the primor…
We report on a study of the natural warm inflationary paradigm (WNI). We show two important new results arise in this model. One is that the observational constraints on the primordial power spectrum from the cosmic microwave background (CMB) can be satisfied without going beyond the Planck scale of the effective field theory. The second is that WNI can inevitably provide perfect conditions for the production of primordial black holes (PBHs) in the golden window of black-hole mass range ($10^{-16} -10^{-11}M_{\odot}$) where it can account for all of the the dark matter content of the universe …
In warm inflation, dissipation due to the interactions of the inflaton field to other light degrees of freedom leads naturally to the enhancement of the primordial spectrum during the last 10-20 efolds of inflation. We study this effect in a variant of the Warm Little Inflaton model, where the inflaton couples to light scalars, with a quartic chaotic potential. These large fluctuations on re-entry will form light, evaporating Primordial Black Holes, with masses lighter than $10^6$ g. But at the same time they will act as a source for the tensors at second order. The enhancement is maximal near…
We compute the primordial curvature spectrum generated during warm inflation, including shear viscous effects. The primordial spectrum is dominated by the thermal fluctuations of the radiation bath, sourced by the dissipative term of the inflaton field. The dissipative coefficient Υ, computed from first principles in the close-to-equilibrium approximation, depends in general on the temperature T, and this dependence renders the system of the linear fluctuations coupled. Whenever the dissipative coefficient is larger than the Hubble expansion rate H, there is a growing mode in the fluctuations …
Next generation of cosmological observations are expected to improve the measurements of several quantities connected to the primordial inflation in the early Universe. These quantities include for example improved measurements for the spectral index of the scalar curvature of the primordial power spectrum and to also bring a better understanding on the scaling dependence of the primordial spectrum. This includes the running of the tilt and, possibly, also the running of the running. In this paper, we investigate the possibility of generating large runnings in the context of warm inflation. Us…
The mechanism of the generation of dark matter and dark radiation from the evaporation of primordial black holes is very interesting. We consider the case of Kerr black holes to generalize previous results obtained in the Schwarzschild case. For dark matter, the results do not change dramatically and the bounds on warm dark matter apply similarly: in particular, the Kerr case cannot save the scenario of black hole domination for light dark matter. For dark radiation, the expectations for $ΔN_{eff}$ do not change significantly with respect to the Schwarzschild case, but for an enhancement in th…
Primordial black holes can represent all or most of the dark matter in the window $10^{17}-10^{22}\,$g. Here we present an extension of the constraints on PBHs of masses $10^{13}-10^{18}\,$g arising from the isotropic diffuse gamma ray background. Primordial black holes evaporate by emitting Hawking radiation that should not exceed the observed background. Generalizing from monochromatic distributions of Schwarzschild black holes to extended mass functions of Kerr rotating black holes, we show that the lower part of this mass window can be closed for near-extremal black holes.
We analyze the processes relevant for star formation in a model with dark matter in the form of sterile neutrinos. Sterile neutrino decays produce an X-ray background radiation that has a two-fold effect on the collapsing clouds of hydrogen. First, the X-rays ionize the gas and cause an increase in the fraction of molecular hydrogen, which makes it easier for the gas to cool and to form stars. Second, the same X-rays deposit a certain amount of heat, which could, in principle, thwart the cooling of gas. We find that, in all the cases we have examined, the overall effect of sterile dark matter …
Analytic formulas reproducing the warm dark matter (WDM) primordial spectra are obtained for WDM particles decoupling in and out of thermal equilibrium which provide the initial data for WDM non-linear structure formation. We compute and analyze the corresponding WDM overdensities and compare them to the CDM case. We consider the ratio of the WDM to CDM primordial spectrum and the WDM to CDM overdensities: they turn to be self-similar functions of k/k_{1/2} and R/R_{1/2} respectively, k_{1/2} and R_{1/2} being the wavenumber and length where the WDM spectrum and overdensity are 1/2 of the resp…
Stochastic gravitational waves can be induced from the primordial curvature perturbations generated during inflation, through scalar-tensor mode coupling at the second order of cosmological perturbation theory. Here we discuss a model of warm inflation in which large curvature perturbations are generated at the small scales because of inflaton dissipation. These overdense perturbations then collapse at later epoch to form primordial black holes, as was studied in our earlier work (Ref. \cite{Arya:2019wck}), and therefore may also act as a source to the second-order tensor perturbations. In thi…
Motivated by some of the recent swampland conjectures, we study the implementation for the late time acceleration of the Universe of a mechanism developed by Anber and Sorbo in the context of primordial inflation, in which an axion field can slowly roll in a steep potential due to additional friction provided by its coupling to some U(1) gauge field. We first study the realization of this mechanism in N = 2 supergravity models resulting from string compactifications on Calabi--Yau manifolds. We then study the transition between matter domination and the axion domination, and show that indeed t…
Dark matter coupled solely gravitationally can be produced through the decay of primordial black holes in the early universe. If the dark matter is lighter than the initial black hole temperature, it could be warm enough to be subject to structure formation constraints. In this paper we perform a more precise determination of these constraints. We first evaluate the dark matter phase-space distribution, without relying on the instantaneous decay approximation. We then interface this phase-space distribution with the Boltzmann code CLASS to extract the corresponding matter power spectrum, which…
We study the effects of primordial magnetic fields on the inflationary potential in the context of a warm inflation scenario. The model, based on global supersymmetry with a new-inflation-type potential and a coupling between the inflaton and a heavy intermediate superfield, is already known to preserve the flatness required for slow-roll conditions even after including thermal contributions. Here we show that the magnetic field makes the potential even flatter, retarding the transition and rendering it smoother.
The 511 keV gamma emission from the galactic core may originate from a high concentration ($\sim 10^{22}$) of primordial black holes (PBHs) in the core each of whose Hawking radiation includes $\sim 10^{21}$ positrons per second. The PBHs we consider are taken as near the lightest with longevity greater than the age of the universe (mass $\sim 10^{12}$ kg; Schwarzschild radius $\sim 1$ fm). These PBHs contribute only a small fraction of cold dark matter, $Ω_{PBH} \sim 10^{-8}$. This speculative hypothesis, if confirmed implies the simultaneous discovery of Hawking radiation and an early univer…
Primordial black holes in the mass range from $10^{-5}$ to $10^9$ g might have existed in the early universe. Via their evaporation mechanism (completed before Big Bang Nucleosynthesis), they might have released stable particles beyond the Standard Model. We reconsider the possibility that such particles might constitute the main part or a fraction of the dark matter observed today, updating the impact on this scenario from warm dark matter constraints. If sufficiently light, stable particles from primordial black holes evaporation might also provide a significant contribution to dark radiatio…
We make use of the phase space density approach to discuss gravitino as a warm dark matter candidate. Barring fine tuning between the reheat temperature in the Universe and superparticle masses, we find that \emph{warm} gravitinos have both appropriate total mass density, Omega_{\tilde G} = Ω_{DM} \simeq 0.2, and suitable primordial phase space density at low momenta provided that their mass is in the range 1 keV \lesssim \mg \lesssim 15 keV, the reheat temperature in the Universe is low, T_R \lesssim 10 TeV, and masses of some of the superparticles are sufficiently small, M \lesssim 350 GeV. …
Primordial black holes (PBHs) in the mass range $(30$--$100)~M_{\odot}$ are interesting candidates for dark matter, as they sit in a narrow window between microlensing and cosmic microwave background constraints. There are however tight constraints from the binary merger rate observed by the LIGO and Virgo experiments. In deriving these constraints, PBHs were treated as point Schwarzschild masses, while the more careful analysis in an expanding universe we present here, leads to a time-dependent mass. This implies a stricter set of conditions for a black hole binary to form and means that blac…
Observations of the temperature anisotropies in the Cosmic Microwave Background (CMB) radiation show that the models of inflation with the monomial potentials are inconsistent with the allowed $n_s-r$ bounds. However certain monomial potentials of inflation are allowed in the context of \textit{Warm Inflation}, where the inflaton's coupling with other fields are significant both \textit{during and after} the inflationary phase. In our study, we consider $λϕ^4$ and $λϕ^6$ models of warm inflation with different forms of the inflaton dissipation coefficient. We parameterize the primordial power …
We entertain the possibility that primordialblack holes of mass $\sim (10^{26}$--$10^{29})$~g, with Schwarzschild radii of $\mathcal{O}{\text{cm}}$, constitute $\sim 10\%$ or more of cosmic dark matter, as allowed by various constraints. These black holes would typically originate from cosmological eras corresponding to temperatures $\mathcal{O}{10-100}$~GeV, and may be associated with first order phase transitions in the visible or hidden sectors. In case these small primordial black holes get captured in orbits around neutron stars or astrophysical black holes in our galactic neighborhood, g…
We explore the range of parameters for dark-matter sterile neutrinos in an extention of the Minimal Standard Model by three singlet fermions with masses below the electroweak scale (the $ν$MSM). This simple model can explain a wide range of phenomena, including neutrino oscillations, baryogenesis, the pulsar velocities, and the early reionization. The presence of two heavier sterile neutrinos and the possibility of entropy production in their decays broadens the allowed range of parameters for the dark-matter sterile neutrinos (or other types of dark matter, for example, the gravitino). In add…
About eight minutes before a black hole expires it has a decreasing mass of 10^{10} g, an increasing temperature of 1 TeV, and an increasing luminosity of 7x10^{27} erg/s. I show that such a black hole is surrounded by a quasi-stationary shell of matter undergoing radial hydrodynamic expansion. The inner radius of this shell is bounded by ten times the Schwarzschild radius of 1.6x10^{-5} fm and has a temperature about one-tenth that of the black hole. The outer radius, as defined by the photosphere, is about 1000 fm, has a local temperature of 100 keV, and is moving with a Lorentz gamma factor…
In this paper, we extend the idea that the spectrum of Hawking radiation can reveal valuable information on a number of parameters that characterize a particular black hole background - such as the dimensionality of spacetime and the value of coupling constants - to gain information on another important aspect: the curvature of spacetime. We investigate the emission of Hawking radiation from a D-dimensional Schwarzschild-de-Sitter black hole emitted in the form of scalar fields, and employ both analytical and numerical techniques to calculate greybody factors and differential energy emission r…
Hawking evaporation of black holes in the early Universe is expected to copiously produce all kinds of particles, regardless of their charges under the Standard Model gauge group. For this reason, any fundamental particle, known or otherwise, could be produced during the black hole lifetime. This certainly includes dark matter (DM) particles. This paper improves upon previous calculations of DM production from primordial black holes (PBH) by consistently including the greybody factors, and by meticulously tracking a system of coupled Boltzmann equations. We show that the initial PBH densities …
Warm dark matter (WDM) may resolve the possible conflict between observed galaxy halos and the halos produced in cold dark matter (CDM) simulations. Here we present an extension of MSSM to include WDM by adding a gauge singlet fermion, \barχ, with a portal-like coupling to the MSSM Higgs doublets. This model has the property that the dark matter is {\it necessarily warm}. In the case where M_{\barχ} is mainly due to electroweak symmetry breaking, the \barχ mass is completely determined by its relic density and the reheating temperature, T_R. For 10^2 GeV < T_{R} < 10^{5} GeV$, the range allowe…
Braneworld black holes existing today may be of primordial origin, or may even be produced in high energy particle collisions in the laboratory and in cosmic ray showers as well. These black holes obey a modified mass-radius relationship compared to standard Schwarzschild black holes. Using the variational principle we calculate the bending angle of a light ray near the horizon of a braneworld black hole in the weak field limit. We next derive the expressions of several lensing quantities like the Einstein radius and the magnification for a point light source. These expressions are modified co…
