arXiv subjects

Indranil Dasgupta

Publications and source records attributed to Indranil Dasgupta.

8 recordsLinked to original sources

arXiv1998

Chiral Symmetry Breaking in 2+1 dimensions due to Sphalerons

In 2+1 dimensional gauge thories with $SU(N_c)$ color and $2N_f$ flavors of quarks in the fundamental representation, sphalerons, if present may lead to quark condensation and chiral symmetry breaking. The effect is similar to instanton induced chiral symmetry breaking in 3+1 dimensions and is due to the interaction of quark propagators with sphalerons. The existence of sphalerons requires that color symmetries be broken by a Higgs in the fundamental representation. We show that the sphaleron effect may persist for arbitrarily large $N_f$ but vanishes along with the mass of the gauge fields corresponding to broken generators of $SU(N_c)$. The effect is inherently non-Abelian and absent for QED.

hep-ph↗

arXiv1998

The imaginary time Path Integral and non-time-reversal-invariant- saddle points of the Euclidean Action

We discuss new bounce-like (but non-time-reversal-invariant-) solutions to Euclidean equations of motion, which we dub boomerons. In the Euclidean path integral approach to quantum theories, boomerons make an imaginary contribution to the vacuum energy. The fake vacuum instabilty can be removed by cancelling boomeron contributions against contributions from time reversed boomerons (anti-boomerons). The cancellation rests on a sign choice whose significance is not completely understood in the path integral method.

hep-th↗

arXiv1997

Vacuum Tunneling by Cosmic Strings

We consider vacuum tunneling of a new kind where the false vacua are not translationally invariant, but have topological defects that break some of their translational symmetries. In the particular case where the topological defects are cosmic strings, we show the existence of an O(2) \times O(2) symmetric bounce configuration that allows a semi-classical estimate of the rate of cosmic string induced tunneling. A method of reduction is then suggested for simplifying the computation of the bounce action. Some phenomenological applications are described.

hep-th↗

arXiv1997

Estimating Vacuum Tunneling Rates

We show that in Euclidean field theories that have bounce solutions, the bounce with the least action is the global minimum of the action in an open space of field configurations. A rigorous upper bound on the minimal bounce action can therefore be obtained by finite numerical methods. This sets a lower bound on the tunneling rate which, fortunately, is often the more interesting and useful bound. We introduce a notion of reduction which allows this bound to be computed with less effort by reducing complicated field theories to simpler ones.

hep-ph↗

arXiv1996

Binary String Dynamics

In this paper we investigate the dynamical properties of binary cosmic strings. We find extrinsic curvature dependence of the string action and show that kinks on binary strings are eroded while cusps can play a major role in their evolution.

hep-ph↗

arXiv1996

Baryogenesis from Cosmic Strings at the Electroweak Scale

We explore the viability of baryogenesis from light scalar decays after the electroweak phase transition. A minimal model of this kind is constructed with new CP violating interactions involving a heavy fourth family. The departure from thermal equilbrium must come from topological defects like cosmic strings, and we show that almost any mechanism for producing the cosmic strings at the electroweak scale results in a viable theory. Baryogenesis occurs in the fourth generation but the baryon number is later transported to the visible generations. This mechanism of indirect baryogenesis allows us to satisfy experimental limits on the proton lifetime while still having perturbative baryon number violation at low energies. The fourth family has very small mixing angles which opens the possibility of distinct observable signatures in collider experiments.

hep-ph↗

arXiv1996

Vacuum Instability in Low-Energy Supersymmetry Breaking Models

We show that for the simplest models of gauge mediated supersymmetry breaking, including all existing models, the true vacuum will not preserve QCD if it communicates supersymmetry breaking to the visible sector. We show that the desired supersymmetry breaking color preserving vacuum can nonetheless be stable cosmologically, but only if certain couplings are sufficiently small. We also present simple modifications to the sector which communicates supersymmetry breaking in which the true vacuum is acceptable, suggesting desirable properties to be sought in dynamical models of supersymmetry breaking.

hep-ph↗

arXiv1995

Binary Cosmic Strings

The properties of cosmic strings have been investigated in detail for their implications in early-universe cosmology. Although many variations of the basic structure have been discovered, with implications for both the microscopic and macroscopic properties of cosmic strings, the cylindrical symmetry of the short-distance structure of the string is generally unaffected. In this paper we describe some mechanisms leading to an asymmetric structure of the string core, giving the defects a quasi-two-dimensional character. We also begin to investigate the consequences of this internal structure for the microscopic and macroscopic physics.

hep-th↗