470 research outputs found
Evaporating Kerr black holes as probes of new physics
In the string axiverse scenario, primordial black holes (PBHs) can sustain
non-negligible spin parameters as they evaporate. We show that tracking both
the mass and spin evolution of a PBH in its final hour can yield a purely
gravitational probe of new physics beyond the TeV scale, allowing one to
determine the number of new scalars, fermions, vector bosons, and spin-3/2
particles. Furthermore, we propose a multi-messenger approach to accurately
measure the mass and spin of a PBH from its Hawking photon and neutrino primary
emission spectra, which is independent of putative interactions between the new
degrees of freedom and the Standard Model particles, as well as from the
Earth-PBH distance
Determining the spin of light primordial black holes with Hawking radiation II: high spin regime
We propose a method to determine the mass and spin of primordial black holes
based on measuring the energy and emission rate at the dipolar and quadrupolar
peaks in the primary photon Hawking spectrum, applicable for dimensionless spin
parameters . In particular, we show that the ratio
between the energies of the two peaks is only a function of the black hole
spin, while the ratio between their emission rates depends also on the
line-of-sight inclination. The black hole mass and distance from the Earth may
then be inferred from the absolute values of the peak energies and emission
rates. This method is relevant for primordial black holes born with large spin
parameters that are presently still in the early stages of their evaporation
process
Warming up brane-antibrane inflation
We show that, in constructions with additional intersecting D-branes,
brane-antibrane inflation may naturally occur in a warm regime, such that
strong dissipative effects damp the inflaton's motion, greatly alleviating the
associated eta-problem. We illustrate this for D3-antiD3 inflation in flat
space with additional flavor D7-branes, where for both a Coulomb-like or a
quadratic hybrid potential a sufficient number of e-folds may be obtained for
perturbative couplings and O(10-10^4) branes. This is in clear contrast with
the corresponding cold scenarios, thus setting the stage for more realistic
constructions within fully stabilized compactifications. Such models
generically predict a negligible amount of tensor perturbations and
non-gaussianity f_NL \sim O(10).Comment: 8 pages, 2 figures; version to be published in Physical Review
Scalar field dark matter and the Higgs field
We discuss the possibility that dark matter corresponds to an oscillating scalar field coupled to the Higgs boson. We argue that the initial field amplitude should generically be of the order of the Hubble parameter during inflation, as a result of its quasi-de Sitter fluctuations. This implies that such a field may account for the present dark matter abundance for masses in the range 10^-6 - 10^-4 eV, if the tensor-to-scalar ratio is within the range of planned CMB experiments. We show that such mass values can naturally be obtained through either Planck-suppressed non-renormalizable interactions with the Higgs boson or, alternatively, through renormalizable interactions within the Randall–Sundrum scenario, where the dark matter scalar resides in the bulk of the warped extra-dimension and the Higgs is confined to the infrared brane
Warm Inflation, Neutrinos and Dark matter: a minimal extension of the Standard Model
We show that warm inflation can be realized within a minimal extension of the
Standard Model with three right-handed neutrinos, three complex scalars and a
gauged lepton/B-L U(1) symmetry. This simple model can address all the
shortcomings of the Standard Model that are not related to fine-tuning, within
general relativity, with distinctive experimental signatures that can be probed
in the near future. The inflaton field emerges from the collective breaking of
the U(1) symmetry, and interacts with two of the right-handed neutrinos,
sustaining a high-temperature radiation bath during inflation. The discrete
interchange symmetry of the model protects the scalar potential against large
thermal corrections and leads to a stable inflaton remnant at late times which
can account for dark matter. Consistency of the model and agreement with Cosmic
Microwave Background observations naturally yield light neutrino masses below
0.1 eV, while thermal leptogenesis occurs naturally after a smooth exit from
inflation into the radiation era.Comment: 43 pages (30 main + 13 appendices), 8 figures. Comments are welcom
Superradiance in the sky
We discuss the conditions under which plane electromagnetic and gravitational waves can be amplified by a rotating black hole due to superradiant scattering. We show, in particular, that amplification can occur for low-frequency waves with an incidence angle parametrically close to 0 (or π) with respect to the black hole spin axis and with a parametrically small left (or right) polarization. This is the case of the radiation emitted by a spinning electric/magnetic dipole or gravitational quadrupole orbiting a black hole companion at large radius and co-rotating with the latter. This can yield observable effects of superradiance, for example, in neutron star-stellar mass black hole binaries, as well as in triple systems composed by a compact binary orbiting a central supermassive black hole. Due to superradiance, the total source luminosity in these systems exhibits a characteristic orbital modulation that may lead to significant observational signatures, thus paving the way for testing, in the near future, one of the most peculiar predictions of general relativity
Superradiant axion clouds around asteroid-mass primordial black holes
We analyze the dynamics and observational signatures of axion clouds formed
via the superradiant instability around primordial black holes, focusing on the
mass range kg where the latter may account for all the dark
matter. We take into account the leading effects of axion self-interactions,
showing that, even though these limit the number of axions produced within each
cloud, a large number of superradiant axions become free of the black hole's
gravitational potential and accumulate in the intergalactic medium or even in
the host galaxy, depending on their escape velocity. This means that primordial
black hole dark matter may lead to a sizeable astrophysical population of
non-relativistic axions, with masses ranging from 0.1 eV to 1 MeV, depending on
the primordial black hole mass and spin. We then show that if such axions
couple to photons their contribution to the galactic and extragalactic
background flux, mainly in the X-ray and gamma-ray band of the spectrum, is
already beyond current observational limits for a large range of parameters
that are, therefore, excluded. We finish by showing the prospects of the Athena
X-ray telescope to further probe this co-existence of primordial black holes
and axions.Comment: 21 pages, 5 figure
Solvent-free process for the development of photocatalytic membranes
PTDC/EAM-AMB/30989/2017.This work described a new sustainable method for the fabrication of ceramic membranes with high photocatalytic activity, through a simple sol-gel route. The photocatalytic surfaces, prepared at low temperature and under solvent-free conditions, exhibited a narrow pore size distribution and homogeneity without cracks. These surfaces have shown a highly efficient and reproducible behavior for the degradation of methylene blue. Given their characterization results, the microfiltration photocatalytic membranes produced in this study using solvent-free conditions are expected to effectively retain microorganisms, such as bacteria and fungi that could then be inactivated by photocatalysis.publishe
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