Department of Physics

Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1932

Browse

Start date: 2010End date: 2019

Search Results

Now showing 1 - 10 of 342
  • No Thumbnail Available
    Item
    Spontaneous CP violating quark scattering from asymmetric Z(3) interfaces in QGP
    (2014-06) Das, Arpan
    In this paper, we extend our earlier study of spontaneous CP violating scattering of quarks and anti-quarks from QCD domain walls for the situation when these walls have asymmetric profiles of the Polyakov loop order parameter . Dynamical quarks lead to explicit breaking of symmetry, which lifts the degeneracy of the vacua arising from spontaneous breaking of the symmetry in the quark-gluon plasma (QGP) phase. Resulting domain walls have asymmetric profile of (under reflection for a domain wall centered at the origin). We calculate the background gauge field profile associated with this domain wall profile. Interestingly, even with the asymmetric profile, quark-antiquark scattering from the corresponding gauge field configuration does not reflect this asymmetry. We show that the expected asymmetry in scattering arises when we include the effect of asymmetric profile of on the effective mass of quarks and antiquarks and calculate resultant scattering. We discuss the effects of such asymmetric Z(3) walls in generating quark and antiquark density fluctuations in cosmology, and in relativistic heavy-ion collisions e.g. event-by-event baryon fluctuations.
  • No Thumbnail Available
    Item
    Spontaneous violating quark scattering from asymmetric interfaces in the quark-gluon plasma
    (APS, 2014-12) Das, Arpan
    In this paper, we extend our earlier study of the spontaneous 𝐶⁢𝑃 violating scattering of quarks and antiquarks from QCD 𝑍⁡(3) domain walls for the situation when these walls have asymmetric profiles of the Polyakov loop order parameter 𝑙⁡(𝑥) . Dynamical quarks lead to the explicit breaking of 𝑍⁡(3) symmetry, which lifts the degeneracy of the 𝑍⁡(3) vacua arising from spontaneous breaking of the 𝑍⁡(3) symmetry in the quark-gluon plasma phase. The resulting domain walls have an asymmetric profile of 𝑙⁡(𝑥) (under the reflection 𝑥 →−𝑥 for a domain wall centered at the origin). We calculate the background gauge field profile 𝐴0 associated with this domain wall profile. Interestingly, even with the asymmetric 𝑙⁡(𝑥) profile, quark-antiquark scattering from the corresponding gauge field configuration does not reflect this asymmetry. We show that the expected asymmetry in scattering arises when we include the effect of the asymmetric profile of 𝑙⁡(𝑥) on the effective mass of quarks and antiquarks and calculate the resultant scattering. We discuss the effects of such asymmetric 𝑍⁡(3) walls in generating quark and antiquark density fluctuations in cosmology, and in relativistic heavy-ion collisions, e.g., event-by-event baryon fluctuations.
  • No Thumbnail Available
    Item
    Reaction-diffusion equation for quark-hadron transition in heavy-ion collisions
    (APS, 2015-09) Das, Arpan
    Reaction-diffusion equations with suitable boundary conditions have special propagating solutions which very closely resemble the moving interfaces in a first-order transition. We show that the dynamics of the chiral order parameter for the chiral symmetry breaking transition in heavy-ion collisions, with dissipative dynamics, is governed by one such equation; specifically, the Newell–Whitehead equation. Furthermore, required boundary conditions are automatically satisfied due to the geometry of the collision. The chiral transition is, therefore, completed by a propagating interface, exactly as for a first-order transition, even though the transition actually is a crossover for relativistic heavy-ion collisions. The same thing also happens when we consider the initial confinement-deconfinement transition with the Polyakov loop order parameter. The resulting equation, again with dissipative dynamics, can then be identified with the reaction-diffusion equation known as the FitzHugh–Nagumo equation which is used in population genetics. Observational constraints imply that the entire phase conversion cannot be achieved by such slow moving fronts, and some alternate faster dynamics needs also to be invoked; for example, involving fluctuations. We discuss the implications of these results for heavy-ion collisions. We also discuss possible extensions for the case of the early universe.
  • No Thumbnail Available
    Item
    Probing color superconducting phases and neutron superfluidity via hydrodynamic evolution at FAIR and NICA
    (India International Centre, 2016) Das, Arpan
    High baryon density regions of the cores of neutron stars are expected to have exotic phases such as color superconducting phases. The symmetry breaking pattern of these phases allows for topological vortices. Even in the lower density region of neutron star, neutron superfluid and associated topological vortices play important role in the dynamics of neutron star, e.g. in pulsar timings and glitches. We consider the possibility of formation of these superfluid phases in heavy-ion collision experiments, e.g. at FAIR and NICA, by carrying out Hydrodynamic simulation. Our result shows that existence of superfluid phases can be detected by studying the effect of vortices on power spectrum of flow fluctuations. (
  • No Thumbnail Available
    Item
    Effects of magnetic field on plasma evolution in relativistic heavy-ion collisions
    (APS, 2017-09) Das, Arpan
    Very strong magnetic fields can arise in noncentral heavy-ion collisions at ultrarelativistic energies, and may not decay quickly in a conducting plasma. We carry out relativistic magnetohydrodynamics (RMHD) simulations to study the effects of this magnetic field on the evolution of the plasma and on resulting flow fluctuations in the ideal RMHD limit. Our results show that the magnetic field leads to enhancement in elliptic flow for small impact parameters while it suppresses it for large impact parameters (which may provide a signal for the initial stage magnetic field). Interestingly, we find that magnetic field in localized regions can temporarily increase in time as evolving plasma energy density fluctuations lead to reorganization of magnetic flux. This can have important effects on the chiral magnetic effect. The magnetic field has nontrivial effects on the power spectrum of flow fluctuations. For the very strong magnetic field case, one sees a pattern of even-odd difference in the power spectrum of flow coefficients arising from reflection symmetry about the magnetic field direction if initial state fluctuations are not dominant. We discuss the situation of nontrivial magnetic field configurations arising from collision of deformed nuclei and show that it can lead to anomalous elliptic flow. Special (crossed body-body) configurations of deformed nuclei collisions can lead to the presence of a quadrupolar magnetic field, which can have very important effects on the rapidity dependence of transverse expansion (similar to beam focusing from quadrupole fields in accelerators).
  • No Thumbnail Available
    Item
    Towards laboratory detection of topological vortices in superfluid phases of QCD
    (World Scientific, 2017) Das, Arpan
    Topological defects arise in a variety of systems, e.g. vortices in superfluid helium to cosmic strings in the early universe. There is an indirect evidence of neutron superfluid vortices from the glitches in pulsars. One also expects that the topological defects may arise in various high baryon density phases of quantum chromodynamics (QCD), e.g. superfluid topological vortices in the color flavor locked (CFL) phase. Though vastly different in energy/length scales, there are universal features in the formation of all these defects. Utilizing this universality, we investigate the possibility of detecting these topological superfluid vortices in laboratory experiments, namely heavy-ion collisions (HICs). Using hydrodynamic simulations, we show that vortices can qualitatively affect the power spectrum of flow fluctuations. This can give an unambiguous signal for superfluid transition resulting in vortices, allowing for the check of defect formation theories in a relativistic quantum field theory system, and the detection of superfluid phases of QCD. Detection of nucleonic superfluid vortices in low energy HICs will give opportunity for laboratory controlled study of their properties, providing crucial inputs for the physics of pulsars.
  • No Thumbnail Available
    Item
    Setting initial conditions for inflation with reaction–diffusion equation
    (Springer, 2018-02) Das, Arpan
    We discuss the issue of setting appropriate initial conditions for inflation. Specifically, we consider natural inflation model and discuss the fine tuning required for setting almost homogeneous initial conditions over a region of order several times the Hubble size which is orders of magnitude larger than any relevant correlation length for field fluctuations. We then propose to use the special propagating front solutions of reaction–diffusion equations for localized field domains of smaller sizes. Due to very small velocities of these propagating fronts we find that the inflaton field in such a field domain changes very slowly, contrary to naive expectation of rapid roll down to the true vacuum. Continued expansion leads to the energy density in the Hubble region being dominated by the vacuum energy, thereby beginning the inflationary phase. Our results show that inflation can occur even with a single localized field domain of size smaller than the Hubble size. We discuss possible extensions of our results for different inflationary models, as well as various limitations of our analysis (e.g. neglecting self gravity of the localized field domain).
  • No Thumbnail Available
    Item
    Thermoelectric effect and seebeck coefficient for hot and dense hadronic matter
    (APS, 2019) Das, Arpan
    We investigate the thermoelectric effect for baryon rich plasma produced in heavy ion collision experiments. We estimate the associated Seebeck coefficient for the hadronic matter. Using kinetic theory within relaxation time approximation we calculate the Seebeck coefficient of a hadronic medium with a temperature gradient. The calculation is performed for hadronic matter modeled by the hadron resonance gas model with hadrons and resonance states up to a cutoff in the mass as 2.25 GeV. We argue that the thermoelectric current produced by such effect can produce a magnetic field in heavy ion collision experiments.
  • No Thumbnail Available
    Item
    Confronting nuclear equation of state in the presence of dark matter using GW170817 observation in relativistic mean field theory approach
    (APS, 2019-02) Das, Arpan
    We confront the admixture of dark matter inside a neutron star using gravitational wave constraints coming from binary neutron star merger. We consider a relativistic mean field model including 𝜎 −𝜔 −𝜌 meson interaction with NL3 parametrization. We study fermionic dark matter interacting with nucleonic matter via Higgs portal mechanism. We show that admixture of dark matter inside the neutron star softens the equation state and lowers the value of tidal deformability. Gravitational wave GW170817 observation puts an upper bound on tidal deformability of a binary neutron star with low spin prior at 90% confidence level, which disfavors stiff equation of state such as the Walecka model with NL3 parametrization. However, we show that the Walecka model with NL3 parametrization with a fermionic dark matter component satisfies the tidal deformability bound coming from the GW170817 observation.
  • No Thumbnail Available
    Item
    Pulsars as Weber gravitational wave detectors
    (Elsevier, 2019-04) Das, Arpan
    A gravitational wave (GW) passing through a pulsar will lead to a variation in the moment of inertia of the pulsar affecting its rotation. This will affect the extremely accurately measured spin rate of the pulsar as well as its pulse profile (due to induced wobbling depending on the source direction). The effect will be most pronounced at resonance and should be detectable by accurate observations of the pulsar signal. The pulsar, in this sense, acts as a remotely stationed Weber detector of gravitational waves whose signal can be monitored on earth. With possible GW sources spread around in the universe, pulsars in their neighborhoods can provide us a family of remote detectors all of which can be monitored on earth. Even if GW are detected directly by earth based conventional detectors, such pulsar detectors can provide additional information for accurate determination of the source location. This can be of crucial importance for sources which do not emit any other form of radiation such as black hole mergers. For the GW events already detected by LIGO (and Virgo), we propose that one should look for specific pulsars which would have been disturbed by these events, and will transmit this disturbance via their pulse signals in any foreseeable future. One should be able to predict these future pulsar events with some accuracy so that a focused effort can be made to detect any possible changes in the signals of those specific pulsars.