arXiv subjects

A. K. Mohanty

Publications and source records attributed to A. K. Mohanty.

28 records · Page 2Linked to original sources

arXiv2002

Long range correlations in DNA sequences

The so called long range correlation properties of DNA sequences are studied using the variance analyses of the density distribution of a single or a group of nucleotides in a model independent way. This new method which was suggested earlier has been applied to extract slope parameters that characterize the correlation properties for several intron containing and intron less DNA sequences. An important aspect of all the DNA sequences is the properties of complimentarity by virtue of which any two complimentary distributions (like GA is complimentary to TC or G is complimentary to ATC) have identical fluctuations at all scales although their distribution functions need not be identical. Due to this complimentarity, the famous DNA walk representation whose statistical interpretation is still unresolved is shown to be a special case of the present formalism with a density distribution corresponding to a purine or a pyrimidine group. Another interesting aspect of most of the DNA sequences is that the factorial moments as a function of length exceed unity around a region where the variance versus length in a log-log plot shows a bending. This is a pure phenomenological observation which is found for several DNA sequences with a few exception. Therefore, this length scale has been used as an approximate measure to exclude the bending regions from the slope analyses. The asymmetries in the nucleotide contents or the patchy structure as a possible origin of the long range correlations has also been investigated.

physics.bio-ph↗

arXiv2002

Spinodal decomposition: An alternate mechanism of phase conversion

The scenario of homogeneous nucleation is investigated for a first order quark-hadron phase transition in a rapidly expanding background of quark gluon plasma. It is found that significant supercooling is possible before hadronization begins. This study also suggests that spinodal decomposition competes with nucleation and may provide an alternative mechanism for phase conversion.

hep-ph↗

arXiv2002

Non-perturbative effects in a rapidly expanding quark-gluon plasma

Within first-order phase transitions, we investigate the pre-transitional effects due to the nonperturbative, large-amplitude thermal fluctuations which can promote phase mixing before the critical temperature is reached from above. In contrast with the cosmological quark-hadron transition, we find that the rapid cooling typical of the RHIC and LHC experiments and the fact that the quark-gluon plasma is chemically unsaturated suppress the role of non-perturbative effects at current collider energies. Significant supercooling is possible in a (nearly) homogeneous state of quark gluon plasma.

hep-ph↗

arXiv2001

Hard Photon production from unsaturated quark gluon plasma at two loop level

The hard photon productions from bremsstrahlung and annihilation with scattering that arise at two loop level are estimated from a chemically non-equilibrated quark gluon plasma using the frame work of thermal field theory. Although, the rate of photon production is suppressed due to unsaturated phase space, the above suppression is relatively smaller than expected due to an additional collinear enhancement (arise due to decrease in thermal quark mass) as compared to it's equilibrium counterpart. Interestingly, unlike the one loop case, the reduction in the two loop processes are found to be independent of gluon chemical poential, but strongly depends on quark fugacity. It is also found that, since the phase space suppression is highest for annihilation with scattering, the photon production is entirely dominated by bremsstrahlung mechanism at all energies. This is to be contrasted with the case of the equilibrated plasma where annihilation with scattering dominates the photon production particularly at higher energies.

hep-ph↗

arXiv2001

Nucleation versus Spinodal decomposition in a first order quark hadron phase transition

We investigate the scenario of homogeneous nucleation for a first order quark-hadron phase transition in a rapidly expanding background of quark gluon plasma. Using an improved preexponential factor for homogeneous nucleation rate, we solve a set of coupled equations to study the hadronization and the hydrodynamical evolution of the matter. It is found that significant supercooling is possible before hadronization begins. This study also suggests that spinodal decomposition competes with nucleation and may provide an alternative mechanism for phase conversion particularly if the transition is strong enough and the medium is nonviscous. For weak enough transition, the phase conversion may still proceed via homogeneous nucleation.

hep-ph↗

arXiv2000

Dynamical growth of the hadron bubbles during the quark-hadron phase transition

The rate of dynamical growth of the hadron bubbles in a supercooled baryon free quark-gluon plasma, is evaluated by solving the equations of relativistic fluid dynamics in all regions. For a non-viscous plasma, this dynamical growth rate is found to depend only on the range of correlation $ξ$ of order parameter fluctuation, and the radius $R$ of the critical hadron bubble, the two length scales relevant for the description of the critical phenomena. Further, it is shown that the dynamical prefactor acquires an additive component when the medium becomes viscous. Interestingly, under certain reasonable assumption for the velocity of the sound in the medium around the saddle configuration, the viscous and the non-viscous parts of the prefactor are found to be similar to the results obtained by Csernai-Kapusta and Ruggeri-Friedman (for the case of zero viscosity) respectively.

hep-ph↗

arXiv2000

Inhomogeneous nucleation in quark hadron phase transition

The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles are created due to thermal fluctuations, and can introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For reasonable choices of surface tension and correlation length, as obtained from the lattice QCD calculations, we show that the amount of phase mixing at the critical temperature remains below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a metastable quark-gluon phase (QGP), within an inhomogeneous background populated by an equilibrium distribution of subcritical hadron bubbles. The inhomogeneity of the medium results in a substantial reduction of the nucleation barrier for critical bubbles. Using the corrected nucleation barrier, we estimate the amount of supercooling for different parameters controlling the phase transition, and briefly discuss its implications to cosmology and heavy-ion collisions.

hep-ph↗

arXiv1999

Effect of baryon density on parton production, chemical equilibration and thermal photon emission from quark gluon plasma

The effect of baryon density on parton production processes of $gg\rightleftharpoons ggg$ and $gg\rightleftharpoons q{\bar q}$ is studied using full phase space distribution function and also with inclusion of quantum statistics i.e. Pauli blocking and Bose enhancement factors, in the case of both saturated and unsaturated quark gluon plasma. The rate for the process $gg \rightleftharpoons q{\bar q}$ is found to be much less as compared to the most commonly used factorized result obtained on the basis of classical approximation. This discrepancy, which is found both at zero as well as at finite baryon densities, however, is not due to the lack of quantum statistics in the classical approximation, rather due to the use of Fermi-Dirac and Bose-Einstein distribution functions for partons instead of Boltzmann distribution which is appropriate under such approximation. Interestingly, the rates of parton production are found to be insensitive to the baryo-chemical potential particularly when the plasma is unsaturated although the process of chemical equilibration strongly depends on it. The thermal photon yields, have been calculated specifically from unsaturated plasma at finite baryon density. The exact results obtained numerically are found to be in close agreement with the analytic expression derived using factorized distribution functions appropriate for unsaturated plasma. Further, it is shown that in the case of unsaturated plasma, the thermal photon production is enhanced with increasing baryon density both at fixed temperature and fixed energy density of the quark gluon plasma.

hep-ph↗

arXiv1999

Dissipative phenomena in chemically non-equilibrated quark gluon plasma

The dissipative corrections to the hydrodynamic equations describing the evolution of energy-momentum tensor and parton densities are derived in a simple way using the scaling approximation for the expanding quark gluon plasma at finite baryon density. This procedure has been extended to study the process of chemical equilibration using a set of rate equations appropriate for a viscous quark gluon plasma. It is found that in the presence of dissipation, the temperature of the plasma evolves slower, whereas the quark and gluon fugacities evolve faster than their counterparts in the ideal case without viscosity.

hep-ph↗

arXiv1999

Chemical equilibration and thermal dilepton production from the quark gluon plasma at finite baryon density

The chemical equilibration of a highly unsaturated quark-gluon plasma has been studied at finite baryon density. It is found that in the presence of small amount of baryon density, the chemical equilibration for gluon becomes slower and the temperature decreases less steeply as compared to the baryon free plasma. As a result, the space time integrated yield of dilepton is enhanced if the initial temperature of the plasma is held fixed. Even at a fixed initial energy density, the suppression of the dilepton yields at higher baryo-chemical potential is compensated, to a large extent, by the slow cooling of the plasma.

hep-ph↗