The motion of cosmic strings in the universe leads to the generation of wakes behind them. We stu... more The motion of cosmic strings in the universe leads to the generation of wakes behind them. We study magnetized wakes of cosmic strings moving in the postrecombination plasma. We show that magnetic reconnection can occur in the postshock region. Since the width of the cosmic-string wake is very small, the reconnection occurs over a very short length scale. The reconnection leads to a large amount of kinetic energy being released in the postshock region of the cosmic-string wake. This enhances the kinetic energy released during the reconnection. We make a rudimentary estimate of the kinetic energy released by the magnetic reconnection in cosmic-string wakes and show that it can account for low-energy gamma-ray bursts in the postrecombination era.
The seed of the primordial magnetic field in the early universe has been attributed to various ph... more The seed of the primordial magnetic field in the early universe has been attributed to various physical process in the early universe. In this work we provide a mechanism for the generation of a primordial magnetic field in the early universe via the collapse of $Z(3)$ domains in the quark gluon plasma. The collapse of closed $Z(3)$ domain walls that arise in the deconfined phase of the QCD (above $T\sim 200$ MeV) leads to the generation of vorticity and turbulence. The transmission coefficient of the $u$, $d$ and $s$ are different across the $Z(3)$ walls. This results in charge concentration at the wall boundary. The charge concentration on the boundary and the vorticity in the plasma generate a magnetic field. We estimate the magnitude of the magnetic field generated and find that it is of the order of $10^{17}$ G which is close to the equipartition value. The mechanism is independent of the order of the QCD phase transition.
Signs of turbulence have been observed at the relativistic heavy ion collision at high collision ... more Signs of turbulence have been observed at the relativistic heavy ion collision at high collision energies. We study the signatures of turbulence in this system and find that there are significant departures from isotropic turbulence in the initial stages of the collision. Since the anisotropic fluctuations are sub leading to the isotropic fluctuations, the Kolmogorov spectrum can usually be obtained even for the initial stages. However, the energy spectrum and the temperature fluctuations indicate deviations from isotropic turbulence. Since a strong momentum anisotropy exists between the transverse and the longitudinal plane, we study the energy density spectrum in these two planes. The geometrical anisotropy is reflected in the anisotropic turbulence generated in the rotating plasma and we find that the scaling exponent is different in the two planes. We find that the scaling exponents in the longitudinal plane are independent of centrality while the scaling exponent in the transve...
Formation of topological objects during phase transitions has been discussed extensively in liter... more Formation of topological objects during phase transitions has been discussed extensively in literature. In all these discussions defects and anti-defects form with equal probabilities. In contrast, many physical situations, such as formation of baryons in relativistic heavy-ion collisions at present energies, flux tube formation in superconductors in the presence of external magnetic field, and formation of superfluid vortices in a rotating vessel, require a mechanism which can bias (say) defects over anti-defects. Such a bias can crucially affect defect-anti-defect correlations, apart from its effects on defect density. In this paper we initiate an investigation for the basic mechanism of biased formation of defects. For Skyrmions in 1+1 dimensions, we show that incorporation of a chemical potential term in the effective potential leads to a domain structure where order parameter is spatially varying. We show that this leads to biased formation of Skyrmions.
In this paper, we study temperature fluctuations in the initial stages of the relativistic heavy ... more In this paper, we study temperature fluctuations in the initial stages of the relativistic heavy ion collision using a multiphase transport model. We consider the plasma in the initial stages after collision before it has a chance to equilibrate. We have considered [Formula: see text] collision with a center-of-mass energy of 200 GeV. We use the nonextensive Tsallis statistics to find the entropic index in the partonic stages of the relativistic heavy ion collisions. We find that the temperature and the entropic index have a linear relationship during the partonic stages of the heavy ion collision. This has already been observed in the hadronic phase. A detailed analysis of the dependence of the entropic index on the system shows that for increasing spacetime rapidity, the entropic index of the partonic system increases. The entropic index also depends on the beam collision energy. The calculation of the entropic index from the experimental data fitting of the transverse momenta dea...
Baryon inhomogeneities are generated early in the universe. These inhomogeneities affect the phas... more Baryon inhomogeneities are generated early in the universe. These inhomogeneities affect the phase transition dynamics of subsequent phase transitions, they also affect the nucleosynthesis calculations. We study the decay of the inhomogeneities in the early universe using the diffusion equation in the Friedmann–Lemaître–Robertson–Walker metric. We calculate the interaction cross section of the quarks with the neutrinos, the electrons and the muons and obtain the diffusion coefficients. The diffusion coefficients are temperature dependent. We find that the expansion of the universe causes the inhomogeneities to decay at a faster rate. We find that the baryon inhomogeneities generated at the electroweak epoch have low amplitudes at the time of the quark hadron transition and hence will not affect the phase transition dynamics unless they are generated with a amplitude greater than $$10^{5}$$ 10 5 times the background density. After the quark hadron transition, we include the interacti...
Cosmic strings moving through matter produce wakes where density is higher than the background de... more Cosmic strings moving through matter produce wakes where density is higher than the background density. We investigate the effects of such wakes occurring at the time of a first order quark-hadron transition in the early universe and show that they can lead to separation of quark-gluon plasma phase in the wake region, while the region outside the wake converts to the hadronic phase. Moving interfaces then trap large baryon densities in sheet like regions which can extend across the entire horizon. Typical separation between such sheets, at formation, is of the order of a km. Regions of baryon inhomogeneity of this nature, i.e. having a planar geometry, and separated by such large distance scales, appear to be well suited for the recent models of inhomogeneous nucleosynthesis to reconcile with the large baryon to photon ratio implied by the recent measurements of the cosmic microwave background power spectrum.
Baryon inhomogeneitites formed in the early universe are important as they affect the nucleosynth... more Baryon inhomogeneitites formed in the early universe are important as they affect the nucleosynthesis calculations. Since they are formed much before the nucleosynthesis epoch, neutrino inflation plays a crucial role in damping out these fluctuations. Now neutrinos, in turn, are affected by magnetic fields which may be present in the early universe. In this work we study the evolution of baryonic inhomogeneities due to neutrino induced dissipative processes in the presence of a background magnetic field. We find that at higher temperatures the dissipation of the inhomogeneities are enhanced as the magnetic field increases. Our study also shows that at lower temperatures the same magnetic field may produce less dissipation. Though we limit our study to temperatures below the quark-hadron transition we do establish that magnetic fields present in the early universe affect the dissipation of baryonic inhomogeneities.
It is possible that under certain situations, in a relativistic heavy-ion collision, partons may ... more It is possible that under certain situations, in a relativistic heavy-ion collision, partons may expand out forming a shell like structure. We analyze the process of hadronization in such a picture for the case when the quarkhadron transition is of first order, and argue that the inside region of such a shell must correspond to supercooled (to T = 0) deconfined vacuum. Hadrons from that region escape out, leaving a bubble of pure deconfined vacuum with large vacuum energy. This bubble undergoes relativistic collapse, with highly Lorentz contracted bubble walls, concentrating entire energy into extremely small regions. Eventually bubble walls collide, with the energy being released in the form of particle production. Thermalization of this system can lead to temperatures of the order of several GeV for RHIC energies, and may even exceed the electroweak transition temperature (∼ 100 GeV) for LHC. We discuss implications of such hot spots, most importantly about the possibility of obse...
We study temperature fluctuations in the initial stages of the relativistic heavy ion collision. ... more We study temperature fluctuations in the initial stages of the relativistic heavy ion collision. We obtain the spectrum of the temperature fluctuations for the peripheral collisions, assuming that the fluid is turbulent. We find that the length scale of the temperature fluctuation is of the order of 1.16 fm. We find that while temperature fluctuations in the initial time steps can be fitted with a Gaussian distribution, temperature fluctuations in the later stages can be better fitted with the q-Gaussian distribution. This distribution is associated with the Tsallis statistics. We use the Tsallis statistics to study the turbulence in the relativistic heavy ion collisions. We obtain the value of the entropic index from the temperature spectrum. A detailed analysis of the dependence of the entropic index on the system parameters is done. We compare our results with recent experimental results and find that the general results of the experimental data are in agreement with our results....
Signs of turbulence have been observed at the relativistic heavy ion collision at high collision ... more Signs of turbulence have been observed at the relativistic heavy ion collision at high collision energies. We study the signatures of turbulence in this system and find that there are significant departures from isotropic turbulence in the initial stages of the collision. Since the anisotropic fluctuations are subleading to the isotropic fluctuations, the Kolmogorov spectrum can usually be obtained even for the initial stages. However, the energy spectrum and the temperature fluctuations indicate deviations from isotropic turbulence. Since a strong momentum anisotropy exists between the transverse and the longitudinal plane, we study the energy density spectrum in these two planes. The geometrical anisotropy is reflected in the anisotropic turbulence generated in the rotating plasma and we find that the scaling exponent is different in the two planes. We find that the scaling exponents in the longitudinal plane are independent of centrality while the scaling exponent in the transver...
We study the vorticity patterns in relativistic heavy ion collisions with respect to the collisio... more We study the vorticity patterns in relativistic heavy ion collisions with respect to the collision energy. The collision energy is related to the chemical potential used in the thermal — statistical models that assume approximate chemical equilibrium after the relativistic collision. We use the multiphase transport model (AMPT) to study the vorticity in the initial parton phase as well as the final hadronic phase of the relativistic heavy ion collision. We find that as the chemical potential increases, the vortices are larger in size. Using different definitions of vorticity, we find that vorticity plays a greater role at lower collision energies than at higher collision energies. We also look at other effects of the flow patterns related to the shear viscosity at different collision energies. We find that the shear viscosity obtained is almost a constant with a small decrease at higher collision energies. We also look at the elliptic flow as it is related to viscous effects in the ...
Neutrinos rotating around Abelian Higgs strings will generate a neutral current close to the stri... more Neutrinos rotating around Abelian Higgs strings will generate a neutral current close to the string. As the string moves through the cosmic plasma, the velocity kick generated by the motion of the string will enhance the neutrino current in the wake region. The neutrino current density depends on its distance from the string and is oscillatory in nature. This leads to neutrino density gradients in the plasma. Such a flux of neutrinos with periodic density fluctuations will lead to electron currents in the plasma. The current will act like a cross-perturbation across the cosmic string wake. The perturbation as well as the high Reynolds number of the plasma will result in the generation of magnetic fields in the wake of the cosmic string.
The motion of cosmic strings in the universe leads to the generation of wakes behind them. We stu... more The motion of cosmic strings in the universe leads to the generation of wakes behind them. We study magnetized wakes of cosmic strings moving in the postrecombination plasma. We show that magnetic reconnection can occur in the postshock region. Since the width of the cosmic-string wake is very small, the reconnection occurs over a very short length scale. The reconnection leads to a large amount of kinetic energy being released in the postshock region of the cosmic-string wake. This enhances the kinetic energy released during the reconnection. We make a rudimentary estimate of the kinetic energy released by the magnetic reconnection in cosmic-string wakes and show that it can account for low-energy gamma-ray bursts in the postrecombination era.
The seed of the primordial magnetic field in the early universe has been attributed to various ph... more The seed of the primordial magnetic field in the early universe has been attributed to various physical process in the early universe. In this work we provide a mechanism for the generation of a primordial magnetic field in the early universe via the collapse of $Z(3)$ domains in the quark gluon plasma. The collapse of closed $Z(3)$ domain walls that arise in the deconfined phase of the QCD (above $T\sim 200$ MeV) leads to the generation of vorticity and turbulence. The transmission coefficient of the $u$, $d$ and $s$ are different across the $Z(3)$ walls. This results in charge concentration at the wall boundary. The charge concentration on the boundary and the vorticity in the plasma generate a magnetic field. We estimate the magnitude of the magnetic field generated and find that it is of the order of $10^{17}$ G which is close to the equipartition value. The mechanism is independent of the order of the QCD phase transition.
Signs of turbulence have been observed at the relativistic heavy ion collision at high collision ... more Signs of turbulence have been observed at the relativistic heavy ion collision at high collision energies. We study the signatures of turbulence in this system and find that there are significant departures from isotropic turbulence in the initial stages of the collision. Since the anisotropic fluctuations are sub leading to the isotropic fluctuations, the Kolmogorov spectrum can usually be obtained even for the initial stages. However, the energy spectrum and the temperature fluctuations indicate deviations from isotropic turbulence. Since a strong momentum anisotropy exists between the transverse and the longitudinal plane, we study the energy density spectrum in these two planes. The geometrical anisotropy is reflected in the anisotropic turbulence generated in the rotating plasma and we find that the scaling exponent is different in the two planes. We find that the scaling exponents in the longitudinal plane are independent of centrality while the scaling exponent in the transve...
Formation of topological objects during phase transitions has been discussed extensively in liter... more Formation of topological objects during phase transitions has been discussed extensively in literature. In all these discussions defects and anti-defects form with equal probabilities. In contrast, many physical situations, such as formation of baryons in relativistic heavy-ion collisions at present energies, flux tube formation in superconductors in the presence of external magnetic field, and formation of superfluid vortices in a rotating vessel, require a mechanism which can bias (say) defects over anti-defects. Such a bias can crucially affect defect-anti-defect correlations, apart from its effects on defect density. In this paper we initiate an investigation for the basic mechanism of biased formation of defects. For Skyrmions in 1+1 dimensions, we show that incorporation of a chemical potential term in the effective potential leads to a domain structure where order parameter is spatially varying. We show that this leads to biased formation of Skyrmions.
In this paper, we study temperature fluctuations in the initial stages of the relativistic heavy ... more In this paper, we study temperature fluctuations in the initial stages of the relativistic heavy ion collision using a multiphase transport model. We consider the plasma in the initial stages after collision before it has a chance to equilibrate. We have considered [Formula: see text] collision with a center-of-mass energy of 200 GeV. We use the nonextensive Tsallis statistics to find the entropic index in the partonic stages of the relativistic heavy ion collisions. We find that the temperature and the entropic index have a linear relationship during the partonic stages of the heavy ion collision. This has already been observed in the hadronic phase. A detailed analysis of the dependence of the entropic index on the system shows that for increasing spacetime rapidity, the entropic index of the partonic system increases. The entropic index also depends on the beam collision energy. The calculation of the entropic index from the experimental data fitting of the transverse momenta dea...
Baryon inhomogeneities are generated early in the universe. These inhomogeneities affect the phas... more Baryon inhomogeneities are generated early in the universe. These inhomogeneities affect the phase transition dynamics of subsequent phase transitions, they also affect the nucleosynthesis calculations. We study the decay of the inhomogeneities in the early universe using the diffusion equation in the Friedmann–Lemaître–Robertson–Walker metric. We calculate the interaction cross section of the quarks with the neutrinos, the electrons and the muons and obtain the diffusion coefficients. The diffusion coefficients are temperature dependent. We find that the expansion of the universe causes the inhomogeneities to decay at a faster rate. We find that the baryon inhomogeneities generated at the electroweak epoch have low amplitudes at the time of the quark hadron transition and hence will not affect the phase transition dynamics unless they are generated with a amplitude greater than $$10^{5}$$ 10 5 times the background density. After the quark hadron transition, we include the interacti...
Cosmic strings moving through matter produce wakes where density is higher than the background de... more Cosmic strings moving through matter produce wakes where density is higher than the background density. We investigate the effects of such wakes occurring at the time of a first order quark-hadron transition in the early universe and show that they can lead to separation of quark-gluon plasma phase in the wake region, while the region outside the wake converts to the hadronic phase. Moving interfaces then trap large baryon densities in sheet like regions which can extend across the entire horizon. Typical separation between such sheets, at formation, is of the order of a km. Regions of baryon inhomogeneity of this nature, i.e. having a planar geometry, and separated by such large distance scales, appear to be well suited for the recent models of inhomogeneous nucleosynthesis to reconcile with the large baryon to photon ratio implied by the recent measurements of the cosmic microwave background power spectrum.
Baryon inhomogeneitites formed in the early universe are important as they affect the nucleosynth... more Baryon inhomogeneitites formed in the early universe are important as they affect the nucleosynthesis calculations. Since they are formed much before the nucleosynthesis epoch, neutrino inflation plays a crucial role in damping out these fluctuations. Now neutrinos, in turn, are affected by magnetic fields which may be present in the early universe. In this work we study the evolution of baryonic inhomogeneities due to neutrino induced dissipative processes in the presence of a background magnetic field. We find that at higher temperatures the dissipation of the inhomogeneities are enhanced as the magnetic field increases. Our study also shows that at lower temperatures the same magnetic field may produce less dissipation. Though we limit our study to temperatures below the quark-hadron transition we do establish that magnetic fields present in the early universe affect the dissipation of baryonic inhomogeneities.
It is possible that under certain situations, in a relativistic heavy-ion collision, partons may ... more It is possible that under certain situations, in a relativistic heavy-ion collision, partons may expand out forming a shell like structure. We analyze the process of hadronization in such a picture for the case when the quarkhadron transition is of first order, and argue that the inside region of such a shell must correspond to supercooled (to T = 0) deconfined vacuum. Hadrons from that region escape out, leaving a bubble of pure deconfined vacuum with large vacuum energy. This bubble undergoes relativistic collapse, with highly Lorentz contracted bubble walls, concentrating entire energy into extremely small regions. Eventually bubble walls collide, with the energy being released in the form of particle production. Thermalization of this system can lead to temperatures of the order of several GeV for RHIC energies, and may even exceed the electroweak transition temperature (∼ 100 GeV) for LHC. We discuss implications of such hot spots, most importantly about the possibility of obse...
We study temperature fluctuations in the initial stages of the relativistic heavy ion collision. ... more We study temperature fluctuations in the initial stages of the relativistic heavy ion collision. We obtain the spectrum of the temperature fluctuations for the peripheral collisions, assuming that the fluid is turbulent. We find that the length scale of the temperature fluctuation is of the order of 1.16 fm. We find that while temperature fluctuations in the initial time steps can be fitted with a Gaussian distribution, temperature fluctuations in the later stages can be better fitted with the q-Gaussian distribution. This distribution is associated with the Tsallis statistics. We use the Tsallis statistics to study the turbulence in the relativistic heavy ion collisions. We obtain the value of the entropic index from the temperature spectrum. A detailed analysis of the dependence of the entropic index on the system parameters is done. We compare our results with recent experimental results and find that the general results of the experimental data are in agreement with our results....
Signs of turbulence have been observed at the relativistic heavy ion collision at high collision ... more Signs of turbulence have been observed at the relativistic heavy ion collision at high collision energies. We study the signatures of turbulence in this system and find that there are significant departures from isotropic turbulence in the initial stages of the collision. Since the anisotropic fluctuations are subleading to the isotropic fluctuations, the Kolmogorov spectrum can usually be obtained even for the initial stages. However, the energy spectrum and the temperature fluctuations indicate deviations from isotropic turbulence. Since a strong momentum anisotropy exists between the transverse and the longitudinal plane, we study the energy density spectrum in these two planes. The geometrical anisotropy is reflected in the anisotropic turbulence generated in the rotating plasma and we find that the scaling exponent is different in the two planes. We find that the scaling exponents in the longitudinal plane are independent of centrality while the scaling exponent in the transver...
We study the vorticity patterns in relativistic heavy ion collisions with respect to the collisio... more We study the vorticity patterns in relativistic heavy ion collisions with respect to the collision energy. The collision energy is related to the chemical potential used in the thermal — statistical models that assume approximate chemical equilibrium after the relativistic collision. We use the multiphase transport model (AMPT) to study the vorticity in the initial parton phase as well as the final hadronic phase of the relativistic heavy ion collision. We find that as the chemical potential increases, the vortices are larger in size. Using different definitions of vorticity, we find that vorticity plays a greater role at lower collision energies than at higher collision energies. We also look at other effects of the flow patterns related to the shear viscosity at different collision energies. We find that the shear viscosity obtained is almost a constant with a small decrease at higher collision energies. We also look at the elliptic flow as it is related to viscous effects in the ...
Neutrinos rotating around Abelian Higgs strings will generate a neutral current close to the stri... more Neutrinos rotating around Abelian Higgs strings will generate a neutral current close to the string. As the string moves through the cosmic plasma, the velocity kick generated by the motion of the string will enhance the neutrino current in the wake region. The neutrino current density depends on its distance from the string and is oscillatory in nature. This leads to neutrino density gradients in the plasma. Such a flux of neutrinos with periodic density fluctuations will lead to electron currents in the plasma. The current will act like a cross-perturbation across the cosmic string wake. The perturbation as well as the high Reynolds number of the plasma will result in the generation of magnetic fields in the wake of the cosmic string.
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Papers by Soma Sanyal