arXiv subjects

Madhukar Mishra

Publications and source records attributed to Madhukar Mishra.

5 recordsLinked to original sources

arXiv2026

Testing selectively enhanced QCD axions couplings as an explanation of the RX J1856.5-3754 hard X-ray excess

We explore the possibility of explaining hard X-ray data obtained from one of the Magnificent Seven (M7) neutron-stars (NSs) employing QCD axion-converted photons. The emission of thermal axions along with neutrinos from the core has been considered. We adopt the nucleon-nucleon bremsstrahlung process as the baseline axion production mechanism and Cooper-pair breaking and formation (PBF) as an additional process. We investigate here whether the selectively enhanced QCD axion coupling model can better explain the hard X-ray excess than the commonly used KSVZ axion model. Our results suggest that meV-mass QCD axions cannot explain the hard X-ray observation within the adopted framework. The enhanced selective model in the micro-eV scale provides closer agreement with the hard X-ray data. We thus conclude that the emission of hard X-rays in the $2-8$ keV range from isolated M7 stars could be explained by QCD axions under an enhanced coupling scenario.

hep-ph↗

arXiv2022

Using the non-hydrodynamic mode to study the onset of hydrodynamic behavior in ultraperipheral symmetric nuclear collisions

With the attempts of extending the hydrodynamic framework of heavy-ion collision to proton-proton and other small and low energy systems, we are confronted with the question of how small the system can get and still be safely modelled as a fluid. One of the transport coefficients required in the $2^{nd}$ order relativistic viscous hydrodynamics is the shear relaxation time, inclusion of which solves the causality violation problem in the Navier-Stokes equation. In phenomenological studies this coefficient has been taken as a constant and much attention has gone into finding and fixing the shear viscosity to entropy density ratio, $η/s$. This transport coefficient also happens to control the non-hydrodynamic mode of the out-of-equilibrium hydrodynamics theory. It has been predicted that for decreasing system size, observables become sensitive to variation in shear relaxation time as a result of increasing dominance of non-hydrodynamic mode, which could potentially indicate breakdown of hydrodynamics. In this study, we try to test this prediction in the peripheral Pb-Pb collisions at $2.76$ TeV and Au-Au collisions at $200$ GeV, with IPGlasma initial condition and $(2+1)-$Dimensional viscous hydrodynamics. We find that elliptic flow does show adequate sensitivity to variation in relaxation time for decreasing system size. The multiplicity rapidity density limit for applicability of hydrodynamics is found to be around $dN/dy\approx10$, with the possibility of refinement in this value given a way to improve the centrality resolution in experimental data for referencing in peripheral collisions.

hep-ph↗

arXiv2015

A temperature dependent formation time approach for Υsuppression at LHC

We present here a model to describe the bottomonium suppression in Pb$+$Pb collisions at Large Hadron Collider (LHC), at $\sqrt{s_{NN}}=2.76$ TeV by using the quasi-particle model (QPM) equation of state (EOS) for the Quark-Gluon Plasma (QGP) expanding under Bjorken's hydrodynamical expansion. The current model includes the modification of the formation time based on the temperature of QGP, color screening during bottomonium production, gluon induced dissociation and collisional damping. The cold nuclear matter (CNM) effects and decay of higher resonances of bottomonium have also been included in the present work. The final suppression of the bottomonium states, at mid rapidity is calculated as a function of centrality. The results compare closely with the recent data at Large hadron Collider (LHC) in the mid rapidity region for various centrality bins. {\nd \it Keywords } : Color screening, Gluonic dissociation, Collisional damping, Survival probability, CNM effects\\ {\nd \it PACS numbers } : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa

hep-ph↗

arXiv2013

Bottomonium suppression at $\sqrt{s_{NN}}=2.76$ TeV using model based on color screening and gluonic dissociation with collisional damping

We present a model to explain the bottomonium suppression in Pb+Pb collisions at mid rapidity obtained from Large Hadron Collider (LHC) energy, $\sqrt{s_{NN}}=2.76$ TeV. The model consists of two decoupled mechanisms namely, color screening during bottomonium production followed by gluon induced dissociation along with collisional damping. The quasi-particle model (QPM) is used as equation of state (EOS) for the Quark-Gluon Plasma (QGP) medium. The feed-down from higher $Υ$ states, such as $Υ(1P)$, $Υ(2S)$ and $Υ(2P)$, dilated formation times for bottomonium states and viscous effect of QGP medium are other ingredients included in the current formulation. We further assume that the QGP is expanding according to (1+1)-dimensional Bjorken's boost invariant scaling law. The net suppression (in terms of $p_T$ integrated survival probability) for bottomonium states at mid rapidity is obtained as a function of centrality and the result is then compared both quantitatively and qualitatively with the recent LHC experimental data in the mid rapidity region recently published by CMS collaboration. We find that the current model, based on the Debye color screening plus gluonic dissociation along with collisional damping, better describes the centrality dependence of bottomonium suppression at LHC energy as compared to color screening model alone. \vskip 0.5cm {\nd \it Keywords} : Color screening, Gluonic dissociation, Collisional damping, Survival probability {\nd \it PACS numbers} : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa

hep-ph↗

arXiv2007

Quenching of Hadron Spectra in a chemically equilibrating Quark-Gluon Plasma

Using the Fokker-Planck equation we have studied the drag co-efficient $A(t)$ and the consequent shift $Δp_\perp (L)$ in the transverse momentum due to collisional energy loss of energetic partons while passing through a chemically equilibrating quark-gluon plasma. Based on these we estimate the quenching factor $Q(p_\perp)$ when the medium is undergoing longitudinal expansion governed by master rate equations. In contrast to the case of chemically equilibrated plasma investigated earlier by Mustafa and Thoma \cite{mus} we find less quenching because our calculated $Q(p_\perp)$ is always greater at all momenta. This result is attributed to the weak drag coefficient operating during initial state interactions.

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