arXiv subjects

G. Tasinato

Publications and source records attributed to G. Tasinato.

25 records · Page 2Linked to original sources

arXiv2003

Warped Brane Worlds in Six Dimensional Supergravity

We present warped compactification solutions of six-dimensional supergravity, which are generalizations of the Randall-Sundrum warped brane world to codimension two and to a supersymmetric context. In these solutions the dilaton varies over the extra dimensions, and this makes the electroweak hierarchy only power-law sensitive to the proper radius of the extra dimensions (as opposed to being exponentially sensitive as in the RS model). Warping changes the phenomenology of these models because the Kaluza-Klein gap can be much larger than the internal space's inverse proper radius. We provide examples both for Romans' nonchiral supergravity and Salam-Sezgin chiral supergravity, and in both cases the solutions break all of the supersymmetries of the models. We interpret the solution as describing the fields sourced by a 3-brane and a boundary 4-brane (Romans' supergravity) or by one or two 3-branes (Salam-Sezgin supergravity), and we identify the topological constraints which are required by this interpretation. For both types of solutions the 3-branes are flat for all topologically-allowed values of the brane tensions. We identify the general mechanism for and limitations of the self-tuning of the effective 4D cosmological constant in higher-dimensional supergravity which these models illustrate.

hep-th↗

arXiv2003

Instabilities and Particle Production in S-Brane Geometries

We study the classical stability of a class of S-brane geometries having cosmological horizons. By considering the perturbations of the metric in these geometries we establish that their horizons are unstable in the sense that an observer trying to cross the horizon experiences an infinite flux of radiation at the instant of crossing. The backreaction of this radiation is likely to convert the horizons into curvature singularities, similar to the instability of the internal Cauchy horizon of the Reissner-Nordstrom black hole. We also compute the particle production by the time-dependent fields in the future regions of these geometries, and find that the spectrum of produced particles is thermal, with temperature coinciding with the Hawking temperature computed by euclideanizing the metric in the static region. Possible implications of these results are discussed.

hep-th↗

arXiv2003

Gravitational Interaction of Neutrinos in Models with Large Extra Dimensions

Whenever fields are allowed to propagate in different portions of space-time, the four dimensional theory exhibits an effective violation of the principle of equivalence. We discuss the conditions under which such an effect is relevant for neutrino physics. In the simplest case of compactification on a flat manifold, the effect of gravity is many orders of magnitude too weak and plays no role for solar neutrino oscillation. Instead, it could be important in the study of ultra high-energy neutrinos in cosmic rays. Gravity could also be relevant for lower energy neutrino processes involving bulk sterile states, if the mechanism of compactification is more subtle than that on torii.

hep-ph↗

arXiv2002

Cosmological Spacetimes from Negative Tension Brane Backgrounds

We identify a time-dependent class of metrics with potential applications to cosmology, which emerge from negative-tension branes. The cosmology is based on a general class of solutions to Einstein-dilaton-Maxwell theory, presented in {hep-th/0106120}. We argue that solutions with hyperbolic or planar symmetry describe the gravitational interactions of a pair of negative-tension $q$-branes. These spacetimes are static near each brane, but become time-dependent and expanding at late epoch -- in some cases asymptotically approaching flat space. We interpret this expansion as being the spacetime's response to the branes' presence. The time-dependent regions provide explicit examples of cosmological spacetimes with past horizons and no past naked singularities. The past horizons can be interpreted as S-branes. We prove that the singularities in the static regions are repulsive to time-like geodesics, extract a cosmological `bounce' interpretation, compute the explicit charge and tension of the branes, analyse the classical stability of the solution (in particular of the horizons) and study particle production, deriving a general expression for Hawking's temperature as well as the associated entropy.

hep-th↗

arXiv2002

S-Branes, Negative Tension Branes and Cosmology

A general class of solutions of string background equations is studied and its physical interpretations are presented. These solutions correspond to generalizations of the standard black p-brane solutions to surfaces with curvature k=-1,0. The relation with the recently introduced S-branes is provided. The mass, charge, entropy and Hawking temperature are computed, illustrating the interpretation in terms of negative tension branes. Their cosmological interpretation is discussed as well as their potential instability under small perturbations.

hep-th↗

arXiv2001

Branes on Charged Dilatonic Backgrounds: Self-Tuning, Lorentz Violations and Cosmology

We construct an n+q+2 dimensional background that has dilatonic q-brane singularities and that is charged under an antisymmetric tensor field, the background spacetime being maximally symmetric in n-dimensions with constant curvature k=0,+1,-1. For k=1 the bulk solutions correspond to black q-branes. For k=0,-1 the geometry resembles the `white hole' region of the Reissner-N"ordstrom solution with a past Cauchy horizon. The metric between the (timelike) singularity and the horizon is static whereas beyond the horizon it is cosmological. In the particular case of q=0, we study the motion of a codimension one n-brane in these charged dilatonic backgrounds that interpolate between the original scalar self-tuning and the black hole geometry and provide a way to avoid the naked singularity problem and/or the need of having exotic matter on the brane. These backgrounds are asymmetrically warped and so break 4D Lorentz symmetry in a way that is safe for particle physics but may lead to faster than light propagation in the gravitational sector.

hep-th↗

arXiv2001

Axion and neutrino physics from anomaly cancellation

It has been recently shown that the requirement of anomaly cancellation in a (non-supersymmetric) six-dimensional version of the standard model fixes the field content to the known three generations. We discuss the phenomenological consequences of the cancellation of the local anomalies: the strong CP problem is solved and the fundamental scale of the theory is bounded by the physics of the axion. Neutrinos acquire a mass in the range suggested by atmospheric experiments.

hep-ph↗