June 19, 2001
We have investigated the phase transition and disoriented chiral condensate domain formation in linear sigma model. Solving the Langevin equation for the linear $\sigma$ model, we have shown that for zero mass pions the fields undergo phase transition above a certain temperature ($T_c$). For finite mass pions, there is no phase transition. It was also shown that when the fields, thermalised at temperature above $T_c$ are cooled down sufficiently rapidly, disoriented chiral condensate domains are formed quite late in the evolution, if the pions are assumed to be mass less. For massive pions, no large DCC domain is formed.
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July 28, 2000
We have investigated the phase transition and disoriented chiral condensate domain formation in linear sigma model. Solving the equation of motion for the sigma model fields in contact with a heat bath, we have shown that the fields undergo phase transition above a certain critical temperature(T_c). It was also shown that when the fields thermalised at temperature above T_c are cooled down sufficiently rapidly, disoriented chiral condensate domains are formed quite late in th...
November 1, 1999
Applying a microscopically motivated semi-classical Langevin description of the linear sigma model we investigate for various different scenarios the stochastic evolution of a disoriented chiral condensate (DCC) in a rapidly expanding system. Some particular emphasize is put on the numerical realisation of colored noise in order to treat the underlying dissipative and nonmarkovian stochastic equations of motion. A comparison with an approximate markovian (i.e. instantaneous) ...
September 21, 1998
Applying a Langevin description of the linear sigma model we investigate four different scenarios for the evolution of a disoriented chiral condensate: annealing or quench with initial conditions governed by effective `light' or physical mass pions. We present pion number distributions estimated from the zero mode (i.e. k=0-field) component. The best DCC signal is expected for the quench scenario with initial conditions centered around zero as would be the case of effective l...
June 22, 2001
As the matter produced in a relativistic heavy ion collision cools through the QCD phase transition, the dynamical evolution of the chiral condensate will be driven out of thermal equilibrium. As a prelude to analyzing this evolution, and in particular as a prelude to learning how rapid the cooling must be in order for significant deviations from equilibrium to develop, we present a detailed analysis of the time-evolution of an idealized region of disoriented chiral condensat...
April 7, 1997
Utilizing the Langevin scenario for the linear sigma model we investigate the effect of friction and white noise on the evolution and stability of collective pionic fields in heavy ion collisions. We find that the smaller the volume the more stable pionic fluctuations become (the avergae mass increases). On the other hand the variance of the mass square increases even more, so for a system preheated in 10 fm3 volume individual trajectories do become unstable during a rapid on...
March 13, 1996
It is unlikely to reach at high temperatures the state which is used as the starting point of DCC formation in the quenched approximation. The chiral symmetry is restored in the linear sigma model by Goldstone modes (pions), because such isospin-p-wave states carry more entropy. In this paper we estimate this effect of isospin-angular motion in the mean field approximation assuming equipartition of the energy.
November 1, 2000
Using the Langevin equation for the linear $\sigma$ model, we have investigated the effect of friction and noise on the possible disoriented chiral condensate formation. Friction and noise are supposed to suppress longwavelength oscillations and growth of disoriented chiral condensate domains. Details simulation shows that for heavy ion collisions, interplay of friction and noise occur in such a manner that formation of disoriented chiral condensate domains are enhanced.
August 17, 1999
We investigate the effect of friction on domain formation in disoriented chiral condensate. We solve the equation of motion of the linear sigma model, in the Hartree approximation, including a friction and a white noise term. For quenched initial condition, we find that even in presence of noise and dissipation domain like structure emerges after a few fermi of evolution. Domain size as large as 5 fm can be formed.
July 7, 1994
We consider the quantum state describing theDisoriented Chiral Condensate (DCC), which may be produced in high energy collisions. We show how a mean field treatment of the quantum equations corresponding to the classical linear sigma model leads to a squeezed state description of the pions emerging from the DCC. We examine various squeezed and coherent state descriptions of those pions with particular attention to charge and number fluctuations. We also study the phenomenolog...
April 8, 1999
We investigate the effect of friction on domain formation in disoriented chiral condensate. Including a friction term, we solve the equation of motion of the linear sigma model fields, in the Hartree approximation. With boost-invariance and cylinderical symmetry, irrespective of friction, on average, we donot find any indication of domain like formation with quenched initial condition. However, with or without friction, some events can be found with large instabilities, indic...