Ajit M. Srivastava

The Cosmological Kibble mechanism in the laboratory: String formation in liquid crystals

The production of strings (disclination lines and loops) has been observed by means of the Kibble mechanism of domain (bubble) formation in the isotropic-nematic phase transition of the uniaxial nematic liquid crystal 4-cyano-4-n-pentylbiphenyl. The number of strings formed per bubble is about 0.6. This value is in reasonable agreement with a numerical simulation of the experiment in which the Kibble mechanism is used for the order parameter space of a uniaxial nematic liquid crystal.

Vortex - antivortex pair production in a first order phase transition

We carry out numerical simulation of a first order phase transition in 2+1 dimensions by randomly nucleating bubbles, and study the formation of global U(1) vortices. Bubbles grow and coalesce and vortices are formed at junctions of bubbles via standard Kibble mechanism as well as due to a new mechanism, recently proposed by us, where defect-antidefect pairs are produced due to field oscillations. We make a comparative study of the contribution of both of these mechanisms for vortex production. We find that, for high nucleation rate of bubbles, vortex-antivortex pairs produced via the new mechanism have overlapping configurations, and annihilate quickly; so only those vortices survive till late which are produced via the Kibble mechanism. However, for low nucleation rates, bubble collisions are energetic enough to lead to many well separated vortex-antivortex pairs being produced via the new mechanism. For example, in a simulation involving nucleation of 20 bubbles, a total of 14 non-overlapping vortices and antivortices formed via this new mechanism of pair creation (6 of them being very well separated), as compared to 6 vortices and antivortices produced via the Kibble mechanism. Our results show the possibility that in extremely energetic bubble collisions, such as those in the inflationary models of the early Universe, this new mechanism may drastically affect the defect production scenario.

Baryon-antibaryon production by disordered chiral condensates

We investigate the production of baryons and antibaryons in the central rapidity region of high energy nuclear collisions within the framework of the Skyrme model taking into account the effects of explicit chiral symmetry breaking. We argue that the formation of disordered chiral condensates may lead to enhanced baryon-antibaryon production at low transverse momentum.

ON THE PRODUCTION OF FLUX VORTICES AND MAGNETIC MONOPOLES IN PHASE TRANSITIONS

We examine the basic assumptions underlying a scenario due to Kibble that is widely used to estimate the production of topological defects. We argue that one of the crucial assumptions, namely the geodesic rule, although completely valid for global defects, becomes ill-defined for the case of gauged defects. We address the issues involved in formulating a suitable geodesic rule for this case and argue that the dynamics plays an important role in the production of gauge defects.

Proximal chiral phase transition

We consider the form of the chiral-symmetry-breaking piece of the effective potential in the linear ensuremath{sigma} model. Surprisingly, it allows for a second local minimum at both zero and finite temperatures. Even though chiral symmetry is not exact, and therefore is not restored in a true phase transition at finite temperature, this second minimum can nevertheless mimic many of the effects of a first-order phase transition. We derive a lower limit on the height of the second minimum relative to the global minimum based on cosmological considerations; this limit is so weak as to be practically nonexistent. In high energy nuclear collisions, it may lead to observable effects in Bose-Einstein interferometry due to domain walls and to coherent pion emission.

Resonant production of topological defects

We describe a novel phenomenon in which vortices are produced due to resonant oscillations of a scalar field which is driven by a periodically varying temperature T, with T remaining much below the critical temperature T(c). Also, in a rapid heating of a localized region to a temperature below T(c), far separated vortex and antivortex can form. We compare our results with recent models of defect production during reheating after inflation. We also discuss possible experimental tests of our predictions of topological defect production without ever going through a phase transition.

Boundary Layer Separation and Vortex Creation in Superflow Through Small Orifices

We report on numerical solutions of the Gross-Pitaevskii equation for twodimensional flow of a super fluid condensate through a small orifice. When the super fluid velocity in the center of the orifice exceeds about 60 % of the speed of sound, the flow in the throat of the orifice becomes unstable to a form of boundary layer separation. Low condensate-density regions bulge away from the walls and form the cores of singly quantized vortices. These detach from the boundary and are convected downstream.

Measuring cosmic defect correlations in liquid crystals

From the theory of topological defect formation proposed for the early universe, the so called Kibble mechanism, it follows that the density correlation functions of defects and anti-defects in a given system should be completely determined in terms of a single length scale

Possibility of formation of a disoriented chiral condensate in p p collisions at energies available at the CERN Large Hadron Collider via the reaction-diffusion equation

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Condensed matter analogues of cosmology

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