111 research outputs found
A note on Weyl transformations in two-dimensional dilaton gravity
We discuss Weyl (conformal) transformations in two-dimensional matterless
dilaton gravity. We argue that both classical and quantum dilaton gravity
theories are invariant under Weyl transformations.Comment: 8 pages, accepted for publication in Mod. Phys. Lett.
QCD and spin effects in black hole airshowers
In models with large extra dimensions, black holes may be produced in
high-energy particle collisions. We revisit the physics of black hole formation
in extensive airshowers from ultrahigh-energy cosmic rays, focusing on
collisional QCD and black hole emissivity effects. New results for rotating
black holes are presented. Monte Carlo simulations show that QCD effects and
black hole spin produce no observable signatures in airshowers. These results
further confirm that the main characteristics of black hole-induced airshowers
do not depend on the fine details of micro black hole models.Comment: 6 pages, 2 figures, accepted for publication in Physical Review
Approximate Canonical Quantization for Cosmological Models
In cosmology minisuperspace models are described by nonlinear
time-reparametrization invariant systems with a finite number of degrees of
freedom. Often these models are not explicitly integrable and cannot be
quantized exactly. Having this in mind, we present a scheme for the
(approximate) quantization of perturbed, nonintegrable, time-reparametrization
invariant systems that uses (approximate) gauge invariant quantities. We apply
the scheme to a couple of simple quantum cosmological models.Comment: 16 pages, Latex, accepted for publication in Int. Jou. Mod. Phys.
Supersymmetry versus black holes at the LHC
Supersymmetry and extra dimensions are the two most promising candidates for
new physics at the TeV scale. Supersymmetric particles or extra-dimensional
effects could soon be observed at the Large Hadron Collider. We propose a
simple but powerful method to discriminate the two models: the analysis of
isolated leptons with high transverse momentum. Black hole events are simulated
with the CATFISH black hole generator. Supersymmetry simulations use a
combination of PYTHIA and ISAJET, the latter providing the mass spectrum. Our
results show the measure of the dilepton invariant mass provides a strong
signature to differentiate supersymmetry and black hole events at the Large
Hadron Collider. Analysis of event-shape variables and multilepton events
complement and strengthen this conclusion.Comment: 12 pages, 5 figure
Stability of naked singularities and algebraically special modes
We show that algebraically special modes lead to the instability of naked
singularity spacetimes with negative mass. Four-dimensional negative-mass
Schwarzschild and Schwarzschild-de Sitter spacetimes are unstable. Stability of
the Schwarzschild-anti-de Sitter spacetime depends on boundary conditions. We
briefly discuss the generalization of these results to charged and rotating
singularities.Comment: 6 pages. ReVTeX4. v2: Minor improvements and extended discussion on
boundary conditions. Version to appear in Phys. Rev.
Prediction of Protein–Protein Interactions Between Alsin DH/PH and Rac1 and Resulting Protein Dynamics
Alsin is a protein of 1,657 amino acids known for its crucial role in vesicular trafficking in neurons thanks to its ability to interact with two guanosine triphosphatases, Rac1 and Rab5. Evidence suggests that Rac1 can bind Alsin central region, composed by a Dbl Homology (DH) domain followed by a Pleckstrin Homology (PH) domain, leading to Alsin relocalization. However, Alsin three-dimensional structure and its relationship with known biological functions of this protein are still unknown. In this work, a homology model of the Alsin DH/PH domain was developed and studied through molecular dynamics both in the presence and in the absence of its binding partner, Rac1. Due to different conformations of DH domain, the presence of Rac1 seems to stabilize an open state of the protein, while the absence of its binding partner results in closed conformations. Furthermore, Rac1 interaction was able to reduce the fluctuations in the second conserved region of DH motif, which may be involved in the formation of a homodimer. Moreover, the dynamics of DH/PH was described through a Markov State Model to study the pathways linking the open and closed states. In conclusion, this work provided an all-atom model for the DH/PH domain of Alsin protein; moreover, molecular dynamics investigations suggested underlying molecular mechanisms in the signal transduction between Rac1 and Alsin, providing the basis for a deeper understanding of the whole structure–function relationship for Alsin protein
Canonical and path integral quantisation of string cosmology models
We discuss the quantisation of a class of string cosmology models that are
characterized by scale factor duality invariance. We compute the amplitudes for
the full set of classically allowed and forbidden transitions by applying the
reduce phase space and the path integral methods. We show that these approaches
are consistent. The path integral calculation clarifies the meaning of the
instanton-like behaviour of the transition amplitudes that has been first
pointed out in previous investigations.Comment: 18 pages,2 eps figures, LaTeX2e, macro files included
(epsf.tex,epsf.sty), macros of Classical and Quantum Gravity used; accepted
for publication on Classical and Quantum Gravit
Jet Geometry and Rate Estimate of Coincident Gamma Ray Burst and Gravitational Wave Observations
Short Gamma-Ray Burst (SGRB) progenitors have long been thought to be
coalescing binary systems of two Neutron Stars (NSNS) or a Neutron Star and a
Black Hole (NSBH). The August 17, 2017 detection of the GW170817
gravitational-wave signal by Advanced LIGO and Advanced Virgo in coincidence
with the electromagnetic observation of the SGRB GRB 170817A confirmed this
scenario and provided new physical information on the nature of these
astronomical events. We use SGRB observations by the Neil Gehrels Swift
Observatory Burst Alert Telescope and GW170817/GRB 170817A observational data
to estimate the detection rate of coincident gravitational-wave and
electromagnetic observations by a gravitational-wave detector network and
constrain the physical parameters of the SGRB jet structure. We estimate the
rate of gravitational-wave detections coincident with SGRB electromagnetic
detections by the Fermi Gamma-ray Burst Monitor to be between 0.1 and
0.6 yr in the third LIGO-Virgo observing run and between
0.3 and 1.8 yr for the LIGO-Virgo-KAGRA network at design
sensitivity. Assuming a structured model with a uniform ultra-relativistic jet
surrounded by a region with power-law decay emission, we find the jet
half-opening angle and the power-law decay exponent to be -- and -- at 1 confidence
level, respectively.Comment: 20 pages, 10 figure
Geometrodynamical Formulation of Two-Dimensional Dilaton Gravity
Two-dimensional matterless dilaton gravity with arbitrary dilatonic potential
can be discussed in a unitary way, both in the Lagrangian and canonical
frameworks, by introducing suitable field redefinitions. The new fields are
directly related to the original spacetime geometry and in the canonical
picture they generalize the well-known geometrodynamical variables used in the
discussion of the Schwarzschild black hole. So the model can be quantized using
the techniques developed for the latter case. The resulting quantum theory
exhibits the Birkhoff theorem at the quantum level.Comment: 15 pages, LATE
PP-waves on Superbrane Backgrounds
In this paper we discuss a method of generating supersymmetric solutions of
the Einstein equations. The method involves the embedding of one supersymmetric
spacetime into another. We present two examples with constituent spacetimes
which support "charges", one of which was known previously and the other of
which is new. Both examples have PP-waves as one of the embedding constituents.Comment: 6 pages no figure
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