arXiv subjects

Diego Chialva

Publications and source records attributed to Diego Chialva.

24 records · Page 2Linked to original sources

arXiv2006

Quantum effects in gravitational wave signals from cuspy superstrings

We study the gravitational emission, in Superstring Theory, from fundamental strings exhibiting cusps. The classical computation of the gravitational radiation signal from cuspy strings features strong bursts in the special null directions associated to the cusps. We perform a quantum computation of the gravitational radiation signal from a cuspy string, as measured in a gravitational wave detector using matched filtering and located in the special null direction associated to the cusp. We study the quantum statistics (expectation value and variance) of the measured filtered signal and find that it is very sharply peaked around the classical prediction. Ultimately, this result follows from the fact that the detector is a low-pass filter which is blind to the violent high-frequency quantum fluctuations of both the string worldsheet, and the incoming gravitational field.

hep-th↗

arXiv2005

Warped Reheating in Multi-Throat Brane Inflation

We investigate in some quantitative details the viability of reheating in multi-throat brane inflationary scenarios by estimating and comparing the time scales for the various processes involved. We also calculate within perturbative string theory the decay rate of excited closed strings into KK modes and compare with that of their decay into gravitons; we find that in the inflationary throat the former is preferred. We also find that over a small but reasonable range of parameters of the background geometry, these KK modes will preferably tunnel to another throat (possibly containing the Standard Model) instead of decaying to gravitons due largely to their suppressed coupling to the bulk gravitons. Once tunneled, the same suppressed coupling to the gravitons again allows them to reheat the Standard Model efficiently. We also consider the effects of adding more throats to the system and find that for extra throats with small warping, reheating still seems viable.

hep-th↗

arXiv2005

Cross sections for production of closed superstrings at high energy colliders in brane world models

In brane world string models with large extra dimensions, there are processes where fermion and antifermion (or two gluons) can annihilate producing a light particle (e.g. gluon) carrying transverse momentum and a Kaluza-Klein graviton or an excited closed string that propagates in the extra dimensions. In high energy colliders, this process gives a missing momentum signature. We compute the total cross section for this process within the context of type II superstring theory in the presence of a D brane. This includes all missing energy sources for this string theory model up to s=8M_s^2, and it can be used to put new limits on the string scale M_s.

hep-ph↗

arXiv2004

Search for the most stable massive state in superstring theory

In ten dimensional type II superstring, all perturbative massive states are unstable, typically with a short lifetime compared to the string scale. We find that the lifetime of the average string state of mass M has the asymptotic form T < const.1/(g^2 M). The most stable string state seems to be a certain state with high angular momentum which can be classically viewed as a circular string rotating in several planes ("the rotating ring"), predominantly decaying by radiating soft massless NS-NS particles, with a lifetime T = c_0 M^5/g^2. Remarkably, the dominant channel is the decay into a similar rotating ring state of smaller mass. The total lifetime to shrink to zero size is ~ M^7. In the presence of D branes, decay channels involving open strings in the final state are exponentially suppressed, so the lifetime is still proportional to M^5, except for a D brane at a special angle or flux. For large mass, the spectrum for massless emission exhibits qualitative features typical of a thermal spectrum, such as a maximum and an exponential tail. We also discuss the decay properties of rotating rings in the case of compact dimensions.

hep-th↗

arXiv2004

Long Lived Large Type II Strings: decay within compactification

Motivated also by recent revival of interest about metastable string states (as cosmic strings or in accelerator physics), we study the decay, in presence of dimensional compactification, of a particular superstring state, which was proven to be remarkably long-lived in the flat uncompactified scenario. We compute the decay rate by an exact numerical evaluation of the imaginary part of the one-loop propagator. For large radii of compactification, the result tends to the fully uncompactified one (lifetime T = const M^5/g^2), as expected, the string mainly decaying by massless radiation. For small radii, the features of the decay (emitted states, initial mass dependence,....) change, depending on how the string wraps on the compact dimensions.

hep-th↗

arXiv2003

Decay of long-lived massive closed superstring states: Exact results

We find a one-parameter family of long-lived physical string states in type II superstring theory. We compute the decay rate by an exact numerical evaluation of the imaginary part of the one-loop propagator. Remarkably, the lifetime rapidly increases with the mass. We find a power-law dependence of the form $T = const. g^{-2} Mass^α$, where the value of $α$ depends on the parameter characterizing the state. For the most stable state in this family, one has $α~= 5$. The dominant decay channel of these massive string states is by emission of soft massless particles. The quantum states can be viewed semiclassically as closed strings which cannot break during the classical evolution.

hep-th↗