108 research outputs found

### Hairy Black Holes in Massive Gravity: Thermodynamics and Phase Structure

The thermodynamic properties of a static and spherically symmetric hairy
black hole solution arising in massive gravity with spontaneous Lorentz
breaking are investigated. The analysis is carried out by enclosing the black
hole in a spherical cavity whose surface is maintained at a fixed temperature
$T$. It turns out that the ensemble is well-defined only if the "hair"
parameter $Q$ characterizing the solution is conserved. Under this condition we
compute some relevant thermodynamic quantities, such as the thermal energy and
entropy, and we study the stability and phase structure of the ensemble. In
particular, for negative values of the hair parameter, the phase structure is
isomorphic to the one of Reissner-Nordstrom black holes in the canonical
ensemble. Moreover, the phase-diagram in the plan ($Q,T$) has a line of
first-order phase transition that at a critical value of $Q$ terminates in a
second-order phase transition. Below this line the dominant phase consists of
small, cold black holes that are long-lived and may thus contribute much more
to the energy density of the Universe than what is observationally allowed for
radiating black holes.Comment: 12 pages, 11 figures, relevant references added, match the published
versio

### From Boltzmann equations to steady wall velocities

By means of a relativistic microscopic approach we calculate the expansion
velocity of bubbles generated during a first-order electroweak phase
transition. In particular, we use the gradient expansion of the Kadanoff-Baym
equations to set up the fluid system. This turns out to be equivalent to the
one found in the semi-classical approach in the non-relativistic limit.
Finally, by including hydrodynamic deflagration effects and solving the Higgs
equations of motion in the fluid, we determine velocity and thickness of the
bubble walls. Our findings are compared with phenomenological models of wall
velocities. As illustrative examples, we apply these results to three theories
providing first-order phase transitions with a particle content in the thermal
plasma that resembles the Standard Model.Comment: 40 pages, 8 figures; v2: added references, version published in JCA

### Electroweak vacuum stability and finite quadratic radiative corrections

If the Standard Model (SM) is an effective theory, as currently believed, it
is valid up to some energy scale $\Lambda$ to which the Higgs vacuum
expectation value is sensitive throughout radiative quadratic terms. The latter
ones destabilize the electroweak vacuum and generate the SM hierarchy problem.
For a given perturbative Ultraviolet (UV) completion, the SM cutoff can be
computed in terms of fundamental parameters. If the UV mass spectrum involves
several scales the cutoff is not unique and each SM sector has its own UV
cutoff $\Lambda_i$. We have performed this calculation assuming the Minimal
Supersymmetric Standard Model (MSSM) is the SM UV completion. As a result, from
the SM point of view, the quadratic corrections to the Higgs mass are
equivalent to finite threshold contributions. For the measured values of the
top quark and Higgs masses, and depending on the values of the different
cutoffs $\Lambda_i$, these contributions can cancel even at renormalization
scales as low as multi-TeV, unlike the case of a single cutoff where the
cancellation only occurs at Planckian energies, a result originally obtained by
Veltman. From the MSSM point of view, the requirement of stability of the
electroweak minimum under radiative corrections is incorporated into the
matching conditions and provides an extra constraint on the Focus Point
solution to the little hierarchy problem in the MSSM. These matching conditions
can be employed for precise calculations of the Higgs sector in scenarios with
heavy supersymmetric fields.Comment: 36 pages, 5 figures; v2: logarithm corrections included, figures
improved, references adde

### Bounding the speed of gravity with gravitational wave observations

The time delay between gravitational wave signals arriving at widely
separated detectors can be used to place upper and lower bounds on the speed of
gravitational wave propagation. Using a Bayesian approach that combines the
first three gravitational wave detections reported by the LIGO collaboration we
constrain the gravitational waves propagation speed c_gw to the 90% credible
interval 0.55 c < c_gw < 1.42 c, where c is the speed of light in vacuum. These
bounds will improve as more detections are made and as more detectors join the
worldwide network. Of order twenty detections by the two LIGO detectors will
constrain the speed of gravity to within 20% of the speed of light, while just
five detections by the LIGO-Virgo-Kagra network will constrain the speed of
gravity to within 1% of the speed of light.Comment: Version published in PRL. 5 pages, 3 figure

### Confronting SUSY models with LHC data via electroweakino production

We investigate multi-lepton signals produced by ElectroWeakino (EWino) decays
in the MSSM and the TMSSM scenarios with sfermions, gluinos and non Standard
Model Higgses at the TeV scale, being the Bino electroweak-scale dark matter.
We recast the present LHC constraints on EWinos for these models and we find
that wide MSSM and TMSSM parameter regions prove to be allowed. We forecast the
number of events expected in the signal regions of the experimental
multi-lepton analyses in the next LHC runs. The correlations among these
numbers will help to determine whether future deviations in multi-lepton data
are ascribable to the EWinos, as well as the supersymmetric model they
originate from.Comment: 33 pages, 10 figures, 3 table

### Probing primordial black holes at high redshift with future gravitational wave detector

We analyze the detection prospects for potential Primordial Black Hole Binary
(PBHB) populations buried in the Stellar-Origin Black Hole Binary (SOBHB)
population inferred by the LVK collaboration. We consider different PBHB
population scenarios and several future Gravitational Wave (GW) detectors. To
separate the PBHB component from the SOBHB one, we exploit the prediction that
the PBHB merger rate does not decline as fast as the SOBHB one at high
redshift. However, only a tiny fraction of PBHB events may be resolved
individually, and the sub-threshold events may yield an undetectable Stochastic
GW Background (SGWB). For this reason, we determine the statistical
significance of the PBHB contributions in the number of resolvable events seen
in future Earth-based detectors and the SGWB measured at LISA. We find that the
synergy between these probes will consistently help assess whether or not a
sizeable PBHB population is present.Comment: 31 pages, 8 figure

### Radion dynamics, heavy Kaluza-Klein resonances and gravitational waves

We study the confinement/deconfinement phase transition of the radion field
in a warped model with a polynomial bulk potential. The backreaction of the
radion on the metric is taken into account by using the superpotential
formalism, while the radion effective potential is obtained from a novel
formulation which can incorporate the backreaction. The phase transition leads
to a stochastic gravitational wave background that depends on the energy scale
of the first Kaluza-Klein resonance, $m_{\textrm{KK}}$. This work completes
previous studies in the following aspects: i) we detail the evaluation of the
radion spectrum; ii) we report on the mismatches between the thick wall
approximation and the numerical bounce solution; iii) we include a suppression
factor in the spectrum of sound waves accounting for their finite lifetime;
and, iv) we update the bound on $m_{\textrm{KK}}$ in view of the O3 LIGO and
Virgo data. We find that the forthcoming gravitational wave interferometers can
probe scenarios where $m_{\textrm{KK}} \lesssim 10^9$ TeV, while the O3-run
bounds rule out warped models with $10^4 \textrm{TeV} \lesssim m_{\textrm{KK}}
\lesssim 10^7$ TeV exhibiting an extremely strong confinement/deconfinement
phase transition.Comment: 16 pages, 7 figures; v2 extended version: added references and Figs.
2, 3, 5 and 7 (lower panels), Figs. 6 and 7 (upper panels) updated, extended
discussion in Secs. 3.3, 4, 5 and 6. Talk given by E.Megias at the 9th
International Conference on New Frontiers in Physics (ICNFP 2020), 4 Sep - 2
Oct 2020, Kolymbari, Crete, Greec

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