# Pradip Roy

## Contact Details

NamePradip Roy |
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## Pubs By Year |
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## Pub CategoriesNuclear Theory (42) High Energy Physics - Phenomenology (36) High Energy Astrophysical Phenomena (3) Nuclear Experiment (2) High Energy Physics - Experiment (1) Physics - Plasma Physics (1) |

## Publications Authored By Pradip Roy

Taking an effective $\rho\pi\pi$ interaction, the self energy of $\rho$ at finite temperature in an arbitrary external magnetic field is calculated using the real time formalism of thermal field theory. The effect of temperature and magnetic field on the in-medium spectral functions are studied. The effective mass and dispersion relations are evaluated from the pole of the complete $\rho$ propagator. Read More

We calculate the rho meson mass in a weak magnetic field using effective $\rho\pi\pi$ interaction. It is seen that both $\rho^0$ and $\rho^\pm$ masses decrease with the magnetic field in vacuum. $\rho$ meson dispersion relation has been calculated and shown to be different for $\rho^0$ and $\rho^\pm$. Read More

We calculate the yield of lepton pair production from jet-plasma interaction where the plasma is anisotropic in momentum space. We compare both the $M$ and $p_T$ distributions from such process with the Drell-Yan contribution. It is observed that the invariant mass distribution of lepton pair from such process dominate over the Drell-Yan up to $3$ GeV at RHIC and up to $10$ GeV at LHC. Read More

In this work, we present a calculation of the non-Fermi liquid correction to the specific heat of magnetized degenerate quark matter present at the core of the neutron star. The role of non-Fermi liquid corrections to the neutrino emissivity has been calculated beyond leading order. We extend our result to the evaluation of the pulsar kick velocity and cooling of the star due to such anomalous corrections and present a comparison with the simple Fermi liquid case. Read More

In this work, dispersion relations of $\pi^0$ and $\pi^{\pm}$ have been studied in vacuum in the limit of weak external magnetic field using a phenomenological pion-nucleon $(\pi N)$ Lagrangian. For our purpose, we have calculated the results up to one loop order in self energy diagrams with the pseudoscalar $(PS)$ and pseudovector $(PV)$ pion-nucleon interactions. By assuming weak external magnetic field it is seen that the effective mass of pion gets explicit magnetic field dependence and it is modified significantly for the case of PS coupling. Read More

We have performed a systematic study of $J/\psi$ and $\psi(2S)$ production in $p-p$ collisions at different LHC energies and at different rapidities using the leading order (LO) non-relativistic QCD (NRQCD) model of heavy quarkonium production. We have included the contributions from $\chi_{cJ}$ ($J$ = 0, 1, 2) and $\psi(2S)$ decays to $J/\psi$. The calculated values have been compared with the available data from the four experiments at LHC namely, ALICE, ATLAS, CMS and LHCb. Read More

The effect of initial state momentum-space anisotropy on invariant mass dependence of HBT radii extracted from the leptonpair interferometry is presented here. We have studied the Bose-Einstein Correlation Function (BECF) for two identical virtual photons decaying to leptonpairs at most central collision of LHC energy having fixed transverse momentum of one of the virtual photons ($k_{1T}$= 2 GeV). The {\em free streaming interpolating} model with fixed initial condition has been used for the evolution in anisotropic Quark Gluon Plasma (aQGP) and the relativistic (1+2)d hydrodynamics model with cylindrical symmetry and longitudinal boost invariance has been used for both isotropic Quark Gluon Plasma (iQGP) and hadronic phases. Read More

The recent experimental results on the flow of $J/\psi$ at LHC show that ample amount of charm quarks is present in the quark gluon plasma and probably they are thermalized. In the current study we investigate the effect of thermalized charm quarks on the heavy quark energy loss to leading order in the QCD coupling constant. It is seen that the energy loss of charm quark increases due to the inclusion of thermal charm quarks. Read More

We calculate the wake in charge density and the wake potential due to the passage of a fast parton in an anisotropic quark gluon plasma(AQGP). For the sake of simplicity small $\xi$(anisotropic parameter) limit has been considered. When the velocity($v$) of the jet is parallel to the anisotropy direction(${\hat n}$) and remains below the phase velocity($v_p$), the wake in induced charge density shows a little oscillatory behavior in AQGP, contrary to the isotropic case. Read More

Within the framework of Boltzmann transport equation with a Bhatnagar-Gross-Krook (BGK) collisional kernel, we study the wake potential induced by fast partons traveling through the high-temperature QCD plasma which is anisotropic in momentum-space. We calculate the dielectric response function of a collisional anisotropic quark-gluon plasma (AQGP) for small $\xi$ (anisotropic parameter) limit. Using this, the wake potential for various combinations of the anisotropy parameter ($\xi$) and the collision rate ($\nu$) is evaluated both for parallel and perpendicular directions of motion of the fast parton. Read More

The only way to obtain the space-time structure of heavy ion collision is through the study of two-particle momentum correlations. Thus we have studied the intensity correlation for the photons having fixed transverse momentum of one of the photons ($k_{1T}$= 2 GeV) in anisotropic Quark Gluon Plasma (aQGP) to have an idea about emission zone in presence of initial momentum anisotropy. The {\em free streaming interpolating} model with fixed initial condition has been used for the space-time evolution for most central collision at RHIC energy. Read More

In this work we have derived the expressions of the mean free path (MFP) and emissivity of the neutrinos by incorporating non-Fermi liquid (NFL) corrections upto next to leading order (NLO). We have shown how such corrections affect the cooling of the neutron star composed of quark matter core. Read More

In this work we calculate pulsar kick velocity of magnetized neutron star composed of degenerate quark matter core with non-Fermi liquid (NFL) correction. Both the leading order (LO) and next to leading order (NLO) corrections to the kick velocity have been incorporated. In addition, the NFL corrections to the specific heat of magnetized quark matter have been presented. Read More

We discuss the collective modes due to the propagation of two oppositely moving relativistic jets (dijet) in an anisotropic quark-gluon plasma(AQGP) and compare the results with the case of single jet propagation. For the sake of simplicity, assuming a tsunami-like initial jet distribution, we observe that the dispersion relations for both the stable and unstable modes are altered significantly due to the passage of dijet in comparison with the case of single jet propagation. It has been further demonstrated that the growth rate of instability, due to introduction of dijet in the system, increases compared to the case of single jet case. Read More

We discuss the role of running coupling on the thermal photon yield from quark gluon plasma. It is shown that the photon production rate from the partonic phase is considerably enhanced when running coupling is considered with respect to a fixed value. However, we show by explicit evaluation that although this difference survives the space-time evolution the experimental data cannot distinguish between the two once the hard contribution, which is an essential component of photon production mechanism, is added. Read More

We discuss the characteristics of collective modes induced by relativistic jets in an anisotropic quark-gluon plasma(AQGP). Assuming a tsunami-like initial jet distribution, it is found that the dispersion relations for both the stable and unstable modes are modified substantially due to the passage of jet compared to the case when there is no jet. It has also been shown that the growth rate of instability first increases compared to the no jet case and then completely turned into damping except the case when the jet velocity is perpendicular to the wave vector in which case the instability always grows. Read More

In this work we derive the expressions of the neutrino mean free path(MFP) and emissivity with non Fermi liquid corrections up to next to leading order(NLO) in degenerate quark matter. The calculation has been performed both for the absorption and scattering processes. Subsequently the role of these NLO corrections on the cooling of the neutron star has been demonstrated. Read More

We derive the expression for the collisional energy loss in two stream plasma induced by the fluctuating chromoelectric field. It is revealed that the main contribution here comes from the unstable modes which grow exponentially with time. A strong direction dependence of the energy loss has also been demonstrated. Read More

We calculate the gluon dissociation cross-section in an anisotropic quark gluon plasma expected to be formed due relativistic nucleus-nucleus collisions. The initial rapid longitudinal expansion of the system leads to momentum space anisotropy due which the observables are affected in such a system. We show that the thermally weighted cross-section of gluon dissociation undergoes modification in anisotropic plasma leading to a decreased probability of $J/\psi$ suppression both for RHIC and LHC energies. Read More

We calculate the nuclear modification factor ($R_{AA}$) of light hadrons by taking into account the initial state momentum anisotropy of the quark gluon plasma (QGP) expected to be formed in relativistic heavy ion collisions. Such an anisotropy can result from the initial rapid longitudinal expansion of the matter. A phenomenological model for the space time evolution of the anisotropic QGP is used to obtain the time dependence of the anisotropy parameter $\xi$ and the hard momentum scale, $p_{\rm hard}$. Read More

We discuss the role of collisional energy loss on high $p_T$ photon data measured by PHENIX collaboration by calculating photon yield in jet-plasma interaction. The phase space distribution of the participating jet is dynamically evolved by solving Fokker-Planck equation. We treat the strong coupling constant ($\alpha_s$) as function of momentum and temperature while calculating the drag and diffusion coefficients. Read More

We calculate radiative energy loss of heavy and light quarks in anisotropic medium (static) in first order opacity expansion. Such an anisotropy can result from the initial rapid longitudinal expansion of the matter, created in relativistic heavy ion collisions. Significant dependency of the energy loss on the anisotropy parameter ($\xi$) and the direction of propagation of the partons with respect to the anisotropy axis is found. Read More

We construct density dependent Class $III$ charge symmetry violating (CSV) potential due to mixing of $\pi$-$\eta$ meson with off-shell corrections. The density dependence enters through the non-vanishing $\pi$-$\eta$ mixing driven by both the neutron-proton mass difference and their asymmetric density distribution. The contribution of density dependent CSV potential is found to be appreciably larger than the contribution of vacuum CSV potential. Read More

We calculate the $p_T$ distributions of jet conversion photons from {\em Quark Gluon Plasma} with pre-equilibrium momentum-space anisotropy. A phenomenological model has been used for the time evolution of hard momentum scale $p_{\rm hard}(\tau)$ and anisotropy parameter $\xi(\tau)$. As a result of pre-equilibrium momentum-space anisotropy, we find significant modification of the jet conversion photon $p_T$ distribution. Read More

We calculate rapidity distribution of photons due to Compton and annihilation processes from {\em Quark Gluon Plasma} (QGP) with pre-equilibrium momentum-space anisotropy. We also include contributions from hadronic matter with late stage transverse expansion. A phenomenological model has been used for the time evolution of hard momentum scale $p_{\rm hard}(\tau)$ and anisotropy parameter $\xi(\tau)$. Read More

We calculate transverse momentum distribution of direct photons from various sources by taking into account the initial state momentum anisotropy of {\em Quark-Gluon-Plasma} (QGP) and late stage transverse flow effects. The total photon yield, calculated for various combinations of initial conditions, transition temperatures, is then compared with the recent measurement of photon transverse momentum distribution by the PHENIX collaboration. It is shown that the presence of such an anisotropy can describe the PHENIX photon data better than the isotropic case. Read More

We construct density dependent Class $III$ charge symmetry violating (CSV) potential due to mixing of $\rho$-$\omega$ meson with off-shell corrections. Here in addition to the usual vacuum contribution, the matter induced mixing of $\rho$-$\omega$ is also included. It is observed that the contribution of density dependent CSV potential is comparable to that of the vacuum contribution. Read More

We calculate medium photons due to Compton and annihilation processes in an anisotropic media. The effects of time-dependent momentum-space anisotropy of {\em Quark-Gluon-Plasma} (QGP) on the medium photon production are discussed. Such an anisotropy can results from the initial rapid longitudinal expansion of the matter, created in relativistic heavy ion collisions. Read More

We expose the role of collisional energy loss on high $p_T$ photon data measured by PHENIX collaboration by calculating photon yield in jet plasma interaction. The phase space distribution of the participating jet is dynamically evolved by solving Fokker-Planck equation. It is shown that the data is reasonably well reproduced when contributions from all the relevant sources are taken into account. Read More

We evaluate the nuclear suppression factor, $R_{AA}(p_T)$ for light hadrons by taking into account the collisional energy loss. We show that in the measured $p_T$ domain of RHIC the elastic process is the dominant mechanism for the partonic energy loss. Read More

We calculate photons from jet plasma interaction in a collisional energy loss scenario. It is shown that the PHENIX photon data is well reproduced when photons from initial hard collisions are taken into account. Read More

We construct the charge symmetry violating (CSV) nucleon-nucleon potential induced by the $\rho^0$-$\o$ mixing due to the neutron-proton mass difference driven by the $NN$ loop. Analytical expression for for the two-body CSV potential is presented containing both the central and non- central $NN$ interaction. We show that the $\rho$$NN$ tensor interaction can significantly enhance the charge symmetry violating $NN$ interaction even if momentum dependent off-shell $\rho^0$-$\omega$ mixing amplitude is considered. Read More

Medium modification of pion form factor has been evaluated in asymmetric nuclear matter. It is shown that both the shape and the pole position of the pion form factor in dense asymmetric nuclear matter is different from its vacuum counterpart with $\rho$-$\omega$ mixing. This is due to the density and asymmetry dependent $\rho$-$\omega$ mixing which could even dominate over its vacuum counterpart in matter. Read More

We calculate nuclear suppression factor ($R_{AA}$) for light hadrons by taking only the elastic processes and argue that in the measured $p_T$ domain of RHIC, collisional rather than the radiative processes is the dominant mechanism for partonic energy loss. Read More

We argue that in the measured $p_T$ domain of RHIC, collisional rather than the radiative energy loss is the dominant mechanism for jet quenching. Accordingly we calculate nuclear suppression factor for light hadrons by taking only the elastic energy loss in sharp contrast with the previous calculations where only the radiative loss are considered. Read More

The momentum integrated Boltzmann equation has been used to study the evolution of strangeness of the strongly interacting system formed after the heavy ion collisions at relativistic energies.We argue that the experimentally observed non-monotonic, horn-like structure in the variation of the $K^+/\pi^+$ with colliding energy appears due to the release of large number of colour degrees of freedom. Read More

Average energy loss of light quarks has been calculated in a two stage equilibrium scenario where the quarks are executing Brownian motion in a gluonic heat bath. The evolution of the quark $p_T$ spectra is studied by solving Fokker-Planck equation in an expanding plasma. Results are finally compared with experimentally measured pion $p_T$ spectrum at RHIC. Read More

We extract the effective degrees of freedom that characterize the co-existing phase of quark gluon plasma and hadrons. Experimental data on phi at mid-rapidity is used to set a lower bound to the critical temperature of quark hadron phase transition. The production and evolution of strangeness have been studied by using Boltzmann equation. Read More

The transverse momentum distribution of the direct photons measured by the PHENIX collaboration in $Au + Au$ collisions at $\sqrt{s}=200$ GeV/A has been analyzed. It has been shown that the data can be reproduced reasonably well assuming a deconfined state of thermalized quarks and gluons with initial temperature more than the transition temperature for deconfinement inferred from lattice QCD. The value of the initial temperature depends on the equation of state of the evolving matter. Read More

Charmonium productions in $p-p$ and $A-B$ collisions have been estimated within the ambit of colour evaporation model (CEM). The model parameters have been fixed by fitting the theoretical results with CDF data. The method is then applied to RHIC and LHC energies to obtain the transverse momentum distributions of $J/\psi$, $\psi^{\prime}$ and $\chi_c$. Read More

The partonic energy loss has been calculated taking both the hard and soft contributions for all the $2 \to 2$ processes, revealing the importance of the individual channels. Cancellation of the intermediate separation scale has been exhibited. Subtleties related to the identical final state partons have properly been taken into account. Read More

The productions of muon pairs from the decay of heavy quarkonia have been evaluated for different centrality of the nuclear collisions at LHC energies. The effects of the various comover scenarios on the survival probability of the heavy quarkonia have been considered. The effects of shadowing and comover suppressions on the dilepton spectra originating from the decays of J/\psi is found to be substantial. Read More

We evaluate the photon spectra from the reaction $\pi\rho\ra \pi\gamma$ for the exchange of $\pi$, $\rho$, $\omega$, $\phi$ and $a_1$ as intermediary mesons. It is found that the contributions from the intermediary $a_1$ is more than any other meson exchange processes up to photon energies 2.5 GeV. Read More

We study the effect of in-medium hadronic properties in photon nucleus interactions in the context of shadowing as well as the dilepton spectrum for incident photon energies in the range 1.1- 3 GeV. A reasonable agreement with the experimental data for shadowing is obtained in a scenario of downward spectral shift of the hadrons. Read More

**Category:**Nuclear Theory

Thermal photon emission rates due to meson-nucleon interactions have been evaluated. An exhaustive set of reactions involving p(\bar p), n(\bar n), rho, omega, a_1, pi and eta is seen to provide a sizeable contribution to the emission rate from hot hadronic matter. Contributions from baryonic resonances are found to be negligibly small. Read More

The parameters obtained from the theoretical analysis of the single photon spectra observed by the WA98 collaboration at SPS energies have been used to evaluate the two photon correlation functions. The single photon spectra and the two photon correlations at RHIC energies have also been evaluated, taking into account the effects of the possible spectral change of hadrons in a thermal bath. We find that the ratio $R_{side}/R_{out} \sim 1$ for SPS and $R_{side}/R_{out} <1$ for RHIC energy. Read More

We study the effects of in-medium hadronic properties on shadowing in photon-nucleus interactions in Glauber model as well as in the multiple scattering approach. A reasonable agreement with the experimental data is obtained in a scenario of downward spectral shift of the hadrons. Shadowing is found to be insensitive to the broadening of the spectral functions. Read More

The space-time evolution of the hot and dense matter formed after the collisions of heavy nuclei at ultra-relativistic energies is investigated using (3+1) dimensional hydrodynamical models. The effects of the spectral shift of the hadronic properties are incorporated in the equation of state (EOS) of the evolving matter. In-medium shift of hadronic properties are considered for Quantum Hadrodynamics (QHD) and universal scaling scenarios. Read More

We compare the photon emission rates from hot hadronic matter with in-medium mass shift and Quark Gluon Plasma (QGP). It is observed that the WA98 data can be well reproduced by hadronic initial state with initial temperature $\sim 200$ MeV if the universal scaling of temperature dependent hadronic masses are assumed and the evolution of temperature with time is taken from transport model or (3+1) dimensional hydrodynamics. The data can also be reproduced by QGP initial state with similar initial temperature and non-zero initial radial velocity. Read More

We estimate the photon and dilepton emission rates from hot hadronic matter with in-medium spectral shift and broadening of vector mesons. It is observed that both the WA98 photon data and CERES/NA45 dilepton data can be well reproduced with similar initial conditions. The freeze-out condition has been constrained by the transverse mass spectra of pions and protons measured by the NA49 collaboration. Read More