arXiv subjects

Mahatsab Mandal

Publications and source records attributed to Mahatsab Mandal.

At least 19 recordsLinked to original sources

arXiv2025

A Study on the Specialist Predator with the Allee Effect on the Prey

Predator-prey models in theoretical ecology have a long and complex history, spanning decades of research. Most of the models rely upon simple reproduction and mortality rates associated with different types of functional responses. A key development in this field occurred with the introduction of a density dependent reproduction rate, originally introduced by Allee. In this manuscript, a new function representing the Allee effect is introduced and justified from the ecological point of view. This paper aims to analyze predator-prey models incorporating Holling type-I and II functional responses, influenced by this new Allee function. A rich dynamics shows up in the presence of the said function, including the emergence of the limit cycles through the Hopf bifurcation for a particular parameter domain.

q-bio.PE↗

arXiv2022

Charmonium production in pp collisions at energies available at the CERN Large Hadron Collider

We have performed a systematic study of J/$ψ$ and $ψ$(2S) production in p--p collisions at different Large Hadron Collider (LHC) energies and at different rapidities using the leading order non-relativistic quantum chromodynamics model of heavy quarkonium production. We have included the contributions from hiher excited states decaying to J$ψ$ . The calculated values have been compared with the available data from the four experiments at LHC, namely ALICE, ATLAS, CMS and LHCb. In the case of ALICE, inclusive J/$ψ$ and $ψ$(2S) cross-sections have been calculated by including the feed-down from B mesons using a fixed-order next-to-leading logarithm formalism. It is found that all the experimental cross-sections are well described for $p_{\rm T} >$ 3 GeV within the theoretical uncertainties arising due to the choices of the factorization and renormalization scales.

hep-ph↗

arXiv2018

Effect of external magnetic field on nucleon mass in hot and dense medium : Inverse Magnetic Catalysis in Walecka Model

Vacuum to nuclear matter phase transition has been studied in presence of constant external background magnetic field with the mean field approximation in Walecka model. The anomalous nucleon magnetic moment has been taken into account using the modified "weak" field expansion of the fermion propagator having non-trivial correction terms for charged as well as for neutral particles. The effect of nucleon magnetic moment is found to favour the magnetic catalysis effect at zero temperature and zero baryon density. However, extending the study to finite temperatures, it is observed that the anomalous nuclear magnetic moment plays a crucial role in characterizing the qualitative behaviour of vacuum to nuclear matter phase transition even in case of the weak external magnetic fields . The critical temperature corresponding to the vacuum to nuclear medium phase transition is observed to decrease with the external magnetic field which can be identified as the inverse magnetic catalysis in Walecka model whereas the opposite behaviour is obtained in case of vanishing magnetic moment indicating magnetic catalysis.

hep-ph↗

arXiv2018

Thermal effects on $ρ$ meson properties in an external magnetic field

A detailed study of the analytic structure of 1-loop self energy graphs for neutral and charged $ρ$ mesons is presented at finite temperature and arbitrary magnetic field using the real time formalism of thermal field theory. The imaginary part of the self energy is obtained from the discontinuities of these graphs across the Unitary and Landau cuts, which is seen to be different for $ρ^0$ and $ρ^\pm$. The magnetic field dependent vacuum contribution to the real part of the self energy, which is usually ignored, is found to be appreciable. A significant effect of temperature and magnetic field is seen in the self energy, spectral function, effective mass and dispersion relation of $ρ^0$ as well as of $ρ^\pm$ relative to its trivial Landau shift. However, for charged $ρ$ mesons, on account of the dominance of the Landau term, the effective mass appears to be independent of temperature. The trivial coupling of magnetic moment of $ρ^\pm$ with external magnetic field, when incorporated in the calculation, makes the $ρ^\pm$ to condense at high magnetic field.

hep-ph↗

arXiv2017

Mass modification of hot pions in magnetized dense medium

A phenomenological pion-nucleon interaction is used to obtain pionic mass modification in presence of constant homogeneous magnetic field background at finite temperature and chemical potential in the real time formalism of thermal field theory. The magnetically modified propagator in its complete form is used to obtain the one loop self-energy for pions. For charged pions we find that the effective mass increases with the magnetic field at given temperature and chemical potential. Since the transverse momentum of charged pion is quantized and its contribution to Dyson-Schwinger Equation is large compared to the loop correction, the charged pion mass remains constant with both temperature and chemical potential for a given landau level. In order to unveil the role of the real part of the self-energy, we also calculate the effective mass neglecting the trivial shift. The effective mass for charged pions shows an oscillatory behavior which is attributed to the thermal contribution of the self-energy. It is argued that the magnetic field dependent vacuum contribution to the self-energy influences the behavior of the effective mass both qualitatively and quantitatively. We also find that very large field is necessary for neutral pions to condense.

hep-ph↗

arXiv2017

$ρ^0-ω$ mixing in the presence of a weak magnetic field

We calculate the momentum dependence of the $ρ^0-ω$ mixing amplitude in vacuum with vector nucleon-nucleon interaction in presence of a constant homogeneous weak magnetic field background. The mixing amplitude is generated by the nucleon-nucleon ($NN$) interaction and thus driven by the neutron-proton mass difference along with a constant magnetic field. We find a significant effect of magnetic field on the mixing amplitude. We also calculate the Charge symmetry violating (CSV) $NN$ potential induced by the magnetic field dependent mixing amplitude. The presence of the magnetic field influences the $NN$ potential substantially which can have important consequences in highly magnetized astrophysical compact objects, such as magnetars. The most important observation of this work is that the mixing amplitude is non-zero, leading to positive contribute to the CSV potential if the proton and neutron masses are taken to be equal.

hep-ph↗

arXiv2016

Spectral properties of $ρ$ meson in a magnetic field

We calculate the rho meson mass in a weak magnetic field using effective $ρππ$ interaction. It is seen that both $ρ^0$ and $ρ^\pm$ masses decrease with the magnetic field in vacuum. $ρ$ meson dispersion relation has been calculated and shown to be different for $ρ^0$ and $ρ^\pm$. We also calculate the $ρππ$ decay width and spectral functions of $ρ^0$ and $ρ^\pm$. The width is seen to decrease with $eB$ and the spectral functions become narrower.

nucl-th↗

arXiv2016

Jet-dilepton conversion from an anisotropic quark-gluon plasma

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. Moreover, it is found that the contribution from anistropic quark gluon plasma (AQGP) increases marginally compared to the isotropic QGP. In case of $p_T$-distribution we observe an increase by a factor of $3-4$ in the entire $p_T$-range at RHIC for AQGP. However, at LHC the change in the $p_T$-distribution is marginal as compared to the isotropic case.

hep-ph↗

arXiv2016

Pionic dispersion relations in the presence of a weak magnetic field

In this work, dispersion relations of $π^0$ and $π^{\pm}$ have been studied in vacuum in the limit of weak external magnetic field using a phenomenological pion-nucleon $(πN)$ 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. However, for the PV coupling, only a modest increase in the effective mass is observed. These modified dispersion relations due to the presence of the external field can have substantial influence in the phenomenological aspect of the mesons both in the context of neutron stars as well as relativistic heavy ion collisions.

nucl-th↗

arXiv2015

Effect of thermalized charm on heavy quark energy loss

The recent experimental results on the flow of $J/ψ$ 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. Running coupling has also been implemented to study heavy quark energy loss and we find a modest increase in the heavy quark energy loss due to heavy-heavy scattering at higher temperature to be realized at LHC energies.

hep-ph↗

arXiv2014

Systematic study of Charmonium production in pp collisions at the LHC energies

We have performed a systematic study of $J/ψ$ and $ψ(2S)$ 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 $χ_{cJ}$ ($J$ = 0, 1, 2) and $ψ(2S)$ decays to $J/ψ$. The calculated values have been compared with the available data from the four experiments at LHC namely, ALICE, ATLAS, CMS and LHCb. In case of ALICE, inclusive $J/ψ$ and $ψ(2S)$ cross-sections have been calculated by including the feed-down from $B$ meson using Fixed-Order Next-to-Leading Logarithm (FONLL) formalism. It is found that all the experimental cross-sections are well reproduced for $p_T >$ 4 GeV within the theoretical uncertainties arising due to the choice of the factorization scale. We also predict the transverse momentum distributions of $J/ψ$ and $ψ(2S)$ both for the direct and feed-down processes at the upcoming LHC energies of $\sqrt{s} =$ 5.1 TeV and 13 TeV for the year 2015.

hep-ph↗

arXiv2014

Effect of anisotropy on HBT radii using leptonpair interferometry

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. We found a significant change in the spatial and temporal dimension of the evolving system in presence of initial state momentum-space anisotropy.

nucl-th↗

arXiv2014

Two Photon Correlation in Anisotropic Quark-gluon plasma (aQGP)

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. The variation of Bose-Einstein correlation function (BECF), $C_2$, for two identical photons as a function of $q_{out}$, $q_{side}$ and $q_{long}$ is evaluated. We have restricted our analysis only to QGP phase to know the effect of anisotropy on the correlation function and HBT radii extracted. It is observed that the longitudinal dimension of the reaction zone is mostly affected due to the presence of momentum space anisotropy.

nucl-th↗

arXiv2013

Wake in anisotropic Quark-Gluon Plasma

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 $ξ$(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. With the jet velocity greater than the phase velocity, the oscillatory behavior increases with $ξ$. Also for $v>v_p$ one observes a clear modification of the cone-like structure in presence of anisotropy. For the parallel direction in the backward region, the depth of the wake potential decreases with the increase of $ξ$ for $v v_p$ and $v<v_p$. In the perpendicular direction, the wake potential is symmetric in the forward and backward regions. With the increase of $ξ$, the depth of negative minimum is moving away from the origin irrespective of the jet velocity. On the other hand when the jet velocity is perpendicular to the anisotropy direction, we find significant changes in the case of both wake charge density and potential in comparison to the isotropic case.

hep-ph↗

arXiv2013

Wake potential in collisional anisotropic quark-gluon plasma

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 $ξ$ (anisotropic parameter) limit. Using this, the wake potential for various combinations of the anisotropy parameter ($ξ$) and the collision rate ($ν$) is evaluated both for parallel and perpendicular directions of motion of the fast parton. It is seen that the inclusion of the collision modifies the wake potential and the amount as well as the nature of the potential depends on the combinations of $ξ$ and $ν$

hep-ph↗

arXiv2012

Gluon dissociation of $J/ψ$ in anisotropic {\em Quark-Gluon-Plasma}

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 $J/ψ$ suppression both for RHIC and LHC energies. The dependence of the cross section as well as the survival probability on the direction of propagation of the charmonium with respect to the anisotropy axis are presented. The sensitivity of the survival probability on the initial conditions have also been demonstrated.

hep-ph↗

arXiv2012

Effect of running coupling on photon emission from quark gluon plasma

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.

hep-ph↗

arXiv2012

Dijet induced collective modes in an anisotropic quark-gluon plasma

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. As in the case of single jet propagation, the instability always grows when the jet velocity is perpendicular to the wave vector. We, thus, argue that the introduction of dijet in the AQGP, in general, leads to faster isotropization than single jet propagation.

hep-ph↗