arXiv subjects

Santosh Kumar Das

Publications and source records attributed to Santosh Kumar Das.

7 recordsLinked to original sources

arXiv2026

Anisotropy effects on heavy quark dynamics in Gribov modified gluon plasma

In the early stages of relativistic heavy-ion collisions, the quark-gluon plasma momentum distribution is anisotropic, leading to instabilities driven by chromomagnetic plasma modes. In this work, we consider the anisotropic momentum distribution of the medium constituents to investigate its effects on charm and bottom quark dynamics using the nonperturbative Gribov resummation approach within the Fokker-Planck equation framework. Specifically, we investigate the impact of nonperturbative effects and weak anisotropies on the heavy-quark transport coefficients, accounting for the angular dependence of the anisotropy vector relative to the heavy-quark motion direction. Furthermore, the calculated drag and diffusion coefficients are used to estimate heavy-quark energy loss and the nuclear modification factor, accounting for both elastic and inelastic collisions. Our findings indicate that momentum anisotropy, angular dependence, and nonperturbative effects-captured through the scattering amplitudes-play a significant role in determining the transport properties of heavy quarks.

hep-ph↗

arXiv2020

Finite size effect on Dissociation and Diffusion of chiral partners in Nambu-Jona-Lasinio model

Along with masses of pion and sigma meson modes, their dissociation into quark medium provide a detail spectral structures of the chiral partners. Present article has studied a finite size effect on that detail structure of chiral partners by using the framework of Nambu-Jona-Lasinio model. Through this dissociation mechanism, their diffusions and conductions are also studied. The masses, widths, diffusion coefficients, conductivities of chiral partners are merged at different temperatures in restore phase of chiral symmetry, but merging points of all are shifted in lower temperature, when one introduce finite size effect into the picture. The strengths of diffusions and conductions are also reduced due to finite size consideration.

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arXiv2019

Impact of Glasma on heavy quark observables in nucleus-nucleus collisions at LHC

In the pre-thermal equilibrium stage of relativistic heavy-ion collisions, a strong quasi-classical transverse gluon field emerges at about $τ_0 \simeq 0.1 \, \rm fm/c$ and evolves together with their longitudinal counterparts according to the classical Yang-Mills (CYM) equations. Recently it has been shown that these fields induce a diffusion of charm quarks in momentum space resulting in a tilt of their spectrum without a significant drag. We find that in nucleus-nucleus collisions at LHC such a novel dynamics of charm quarks leads to an initial enhancement of the nuclear modification factor ($R_{AA}$) at $p_T$ larger than 2 GeV$/c$ contrary to the standard lore. Moreover, the same dynamics leads to a larger final elliptic flow ($v_2$) inducing a relation between $R_{AA}$ and $v_2$ that is quite close to the experimental measurements. Our study also shows that such an initial pre-thermal stage is unlikely to be described in terms of a standard drag and diffusion dynamics, because even if one tune such coefficients to reproduce the same $R_{AA}(p_T)$ this would imply a significantly smaller $v_2$.

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arXiv2019

Towards the determination of heavy-quark transport coefficients in quark-gluon plasma

Several transport models have been employed in recent years to analyze heavy-flavor meson spectra in high-energy heavy-ion collisions. Heavy-quark transport coefficients extracted from these models with their default parameters vary, however, by up to a factor of 5 at high momenta. To investigate the origin of this large theoretical uncertainty, a systematic comparison of heavy-quark transport coefficients is carried out between various transport models. Within a common scheme devised for the nuclear modification factor of charm quarks in a brick medium of a quark-gluon plasma, the systematic uncertainty of the extracted drag coefficient among these models is shown to be reduced to a factor of 2, which can be viewed as the smallest intrinsic systematical error band achievable at present time. This indicates the importance of a realistic hydrodynamic evolution constrained by bulk hadron spectra and of heavy-quark hadronization for understanding the final heavy-flavor hadron spectra and extracting heavy-quark drag coefficient. The transverse transport coefficient is less constrained due to the influence of the underlying mechanism for heavy-quark medium interaction. Additional constraints on transport models such as energy loss fluctuation and transverse-momentum broadening can further reduce theoretical uncertainties in the extracted transport coefficients.

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arXiv2019

Classical model for diffusion and thermalization of heavy quarks in a hot medium: memory and out-of-equilibrium effects

We consider a simple model for the diffusion of heavy quarks in a hot bath, modeling the latter by an ensemble of oscillators distributed accorded to either a thermal distribution or to an out-of-equilibrium distribution with a saturation scale. Within this model it is easy to introduce memory effects by changing the distribution of oscillators: we model these by introducing a gaussian distribution, $dN/dω$, which can be deformed continuously from a $δ-$function giving a Markov dissipation to a broad kernel with memory. Deriving the equation of motion of the heavy quark in the bath we remark how dissipation comes out naturally as an effect of the back-reaction on the bath of oscillators. Moreover, the exact solution of this equation allows for the definition of a thermalization time as the time necessary to remove any memory of the initial condition. We find that the broadening the dissipative kernel while keeping the coupling fixed lowers the thermalization time. We also derive the fluctuation-dissipation theorem for the bath, and use this to estimate the kinematic regime in which momentum diffusion of the heavy quark dominates over drift: we find that diffusion is more important as long as $K_0/{\cal E}$ is small, where $K_0$ and ${\cal E}$ denote the initial energy of the heavy quark and the average energy of the bath respectively.

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arXiv2019

Direct flow of heavy mesons as unique probe of the initial Electro-Magnetic fields in Ultra-Relativistic Heavy Ion collisions

In Ultra-relativistic Heavy-Ion Collisions (HICs) very strong initial electro-magnetic (E.M.) fields are created: the order of magnitude of the magnetic field is about $10^{19} \, Gauss$, the most intense field in the Universe, even larger than that of a magnetar. These fields rapidly decrease in time, inducing a drift of particles in the reaction plane. The resulting flow is odd under charge exchange and this allows to distinguish it from the large vorticity of the bulk matter due to the initial angular momentum conservation. Conjointly charm quarks, thanks to their large mass $M_{c}>>Λ_{QCD}$, are produced in hard partonic processes at formation time $τ_f \approx 1\,/\,( 2M_{HQ} )$ which is comparable with the time scale when the E.M. field attains its maximum value. Moreover, with a mass of $M_c \approx 1.3 \,$ GeV there should be no mixing with the chiral magnetic dynamics and the condition $M_c \gg T$ allows charm quarks to have sufficiently large thermalization time, so that they can probe the entire phase-space evolution of the QGP retaining the initial kick given by the E.M. field. We show that such E.M. field entails a transverse motion of charm quarks resulting in a splitting of directed flow $v_1$ of $ D$ and $\bar{D}$ mesons of few percent, i.e. much larger compared to the measured pion one.

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arXiv2018

Diffusion of charm and beauty in the Glasma

Relativistic nuclear collisions offer a unique way to study strong interactions at very high energy. The collision process can be described within the gluon saturation framework as the interaction of two colored glasses, and because of this interaction strong longitudinal gluon fields, namely the Glasma, are produced immediately after the collision. Besides, heavy quarks are also produced in the very early stage and because of their large mass and small concentration, their motion does not affect the evolution of the Glasma, thus behaving as ideal probes of the Glasma itself. We study the evolution of the heavy quarks in the Glasma allegedly produced in high energy p-Pb collisions by solving consistently the equations of motion of the quarks in the evolving Glasma fields. We find that this motion can be understood in terms of diffusion in momentum space, similarly to the random motion of a heavy probe in a hot thermalized medium. We show how the diffusion of heavy probes affects the nuclear modification factor of D and B mesons in p-Pb collisions.

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