arXiv subjects

Amruta Mishra

Publications and source records attributed to Amruta Mishra.

At least 55 records · Page 3Linked to original sources

arXiv2018

Open bottom mesons in asymmetric nuclear matter in presence of strong magnetic fields

The modifications of the masses of the $B$ and $\bar B$ mesons in asymmetric nuclear matter in the presence of strong magnetic fields, are investigated using a chiral effective model. The medium modifications of these open bottom mesons arise due to their interactions with the scalar mesons and the nucleons. In the magnetized nuclear matter, the proton has contributions from the Landau levels. In the chiral effective model, the masses of the $B$ and $\bar B$ are calculated from the leading term, namely the vectorial Weinberg Tomozawa term as well as from the next to leading order contributions, i.e., due to the scalar exchange and the range terms. Due to the Weinberg-Tomozawa term, the $\bar B$ mesons experience an attractive interaction in the symmetric nuclear matter, whereas the $B$ mesons have a repulsive interaction. Inclusion of the contributions from the scalar exchange and the range terms as well, leads to drop of the masses of both $B$ and $\bar B$ mesons. The effect of the isospin asymmetry breaks the mass degeneracy of the $B^+$ and $B^0$ (as well as of the $B^-$ and $\bar {B^0}$) mesons, and its effect is observed to be large at high densities. The effects of anomalous magnetic moments of the nucleons are taken into account in the present study of the masses of the open bottom mesons in magnetized nuclear matter.

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arXiv2018

D mesons in strongly magnetized asymmetric nuclear matter

The medium modifications of the open charm mesons ($D$ and $\bar D$) are studied in isospin asymmetric nuclear matter in the presence of strong magnetic fields, using a chiral effective model. The mass modifications of these mesons in the effective hadronic model, arise due to their interactions with the protons, neutrons and the scalar mesons (non-strange isoscalar $σ$, strange isoscalar, $ζ$ and non-strange isovector, $δ$), in the magnetized nuclear matter. In the presence of magnetic field, for the charged baryon, i.e., the proton, the number density as well as the scalar density have contributions due to the summation over the Landau energy levels. For a given value of the baryon density, $ρ_B$, and isospin asymmetry, the scalar fields are solved self consistently from their coupled equations of motion. The modifications of the masses of the $D$ and $\bar D$ mesons are calculated, from the medium modifications of the scalar fields and the nucleons. The effects of the anomalous magnetic moments of the nucleons on the masses of the open charm mesons are also investigated in the present work. The effects of isospin asymmetry as well as of the anomalous magnetic moments are observed to be prominent at high densities for large values of magnetic fields.

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arXiv2017

Decay widths of bottomonium states in matter -- a field theoretic model for composite hadrons

We compute the in-medium partial decay widths of the bottomonium states to open bottom mesons ($B\bar B$) using a field theoretical model for composite hadrons with quark constituents. These decay widths are calculated by using the explicit constructions for the bottomonium states and the open bottom mesons ($B$ and $\bar B$), and, the quark antiquark pair creation term of the free Dirac Hamiltonian written in terms of the constituent quark field operators. These decay widths in the hadronic medium are calculated as arising from the mass modifications of the bottomonium states and the $B$ and $\bar B$ mesons, obtained in a chiral effective model. The decay amplitude in the present model is multiplied with a strength parameter for the light quark pair creation, which is fitted from the observed vacuum partial decay width of the bottomonium state, $Υ(4S)$ to $B\bar B$. The effects of the isospin asymmetry, the strangeness fraction of the hadronic matter on the decay widths, arising due to the mass modifications due to these effects, have also been studied. There is observed to be appreciable effects from density, and the effects from isospin asymmetry on the parital decay widths of $Υ\rightarrow B\bar B$ are observed to be quite pronounced at high densities. These effects should show up in the asymmetric heavy ion collisions in Compressed baryonic matter (CBM) experiments planned at the future facility at FAIR. The study of the $Υ$ states will, however, require access to energies higher than the energy regime planned at the CBM experiment. The density effects on the decay widths of the bottomonium states should show up in the production of these states, as well as, in dilepton spectra at the Super Proton Synchrotron (SPS) energies.

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arXiv2015

In-medium decay widths of hidden and open charm vector mesons in a field theoretic model for composite hadrons

We calculate the decay widths of the charmonium states, $J/ψ$, $ψ(3686)$ and $ψ(3770)$, to $D\bar D$ pairs, as well as the decay width of $D^* \rightarrow Dπ$, in isospin asymmetric strange hadronic matter, using a field theoretical model for composite hadrons with quark constituents. For this purpose we use the quark antiquark pair creation term of the free Dirac Hamiltonian written in terms of the constituent quark field operators, and use explicit charmonium, $D$, $\bar {D}$, $D^*$ and $π$ states to evaluate the matrix elements for the charmonium as well as $D^*$ decay amplitudes. The medium modifications of the partial decay widths of charmonium to $D\bar D$ pair, arising from the mass modifications of the $D(\bar D)$ and the charmonium states calculated in a chiral effective model, are also included. The effects of the isospin asymmetry, the strangeness fraction of the hadronic matter on the masses of the charmonium states and $D(\bar D)$ mesons and hence on the decay widths, have also been studied. The decay width of $D^* \rightarrow D π$ in the hadronic matter has also been calculated within the composite quark model in the present work, accounting for the medium modifications of the $D$ and $D^*$ masses. The density modifications of the charmonium states and $D(D^*)$ mesons, which are observed to be appreciable at high densities, will be of relevance in the compressed baryonic matter (CBM) experiments at the future facility of FAIR, GSI, where charmed hadrons will be produced by annihilation of antiprotons on nuclei. The interactions of the charmonium states and $D(D^*)$ with the nuclear medium could lead to the possiblility of the formation of exotic bound states of the nuclei with the (excited) charmonium states as well as with $D(D^*)$ mesons.

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arXiv2015

$D_S$ Mesons in Asymmetric Hot and Dense Hadronic Matter

The in-medium properties of $D_S$ mesons are investigated within the framework of an effective hadronic model, which is a generalization of a chiral SU(3) model, to SU(4), in order to study the interactions of the charmed hadrons. In the present work, the $D_s$ mesons are observed to experience net attractive interactions in a dense hadronic medium, hence reducing the masses of the $D_S^+$ and $D_S^-$ mesons from the vacuum values. While this conclusion holds in both nuclear and hyperonic media, the magnitude of the mass drop is observed to intensify with the inclusion of strangeness in the medium. Additionally, in hyperonic medium, the mass degeneracy of the $D_S$ mesons is observed to be broken, due to opposite signs of the Weinberg-Tomozawa interaction term in the Lagrangian density. Along with the magnitude of the mass drops, the mass splitting between $D_S^+$ and $D_S^-$ mesons is also observed to grow with an increase in baryonic density and strangeness content of the medium. However, all medium effects analyzed are found to be weakly dependent on isospin asymmetry and temperature. We discuss the possible implications emanating from this analysis, which are all expected to make a significant difference to observables in heavy ion collision experiments, especially the upcoming Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR), GSI, where matter at high baryonic densities is planned to be produced.

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arXiv2015

Open bottom mesons in hot asymmetric hadronic medium

The in-medium masses and optical potentials of $B$ and ${\bar B}$ mesons are studied in an isospin asymmetric, strange, hot and dense hadronic environment using a chiral effective model. The chiral $SU(3)$ model originally designed for the light quark sector, is generalized to include the heavy quark sector ($c$ and $b$) to derive the interactions of the $B$ and ${\bar B}$ mesons with the light hadrons. Due to large mass of bottom quark, we use only the empirical form of these interactions for the desired purpose, while treating the bottom degrees of freedom to be frozen in the medium. Hence, all medium effects are due to the in-medium interaction of the light quark content of these open-bottom mesons. Both $B$ and $\bar B$ mesons are found to experience net attractive interactions in the medium, leading to lowering of their masses in the medium. The mass degeneracy of particles and antiparticles, ($B^+$, $B^-$) as well as ($B^0$, $\bar {B^0}$), is observed to be broken in the medium, due to equal and opposite contributions from a vectorial Weinberg-Tomozawa interaction term. Addition of hyperons to the medium lowers further the in-medium mass for each of these four mesons, while a non-zero isospin asymmetry is observed to break the approximate mass degeneracy of each pair of isospin doublets. These medium effects are found to be strongly density dependent, and bear a considerably weaker temperature dependence. The results obtained in the present investigation are compared to predictions from the quark-meson coupling model, heavy meson effective theory, and the QCD Sum Rule approach.

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arXiv2014

Bottom-strange mesons in hyperonic matter

The in-medium behavior of bottom-strange pseudoscalar mesons in hot, isospin asymmetric and dense hadronic environment is studied using a chiral effective model. The same was recently generalized to the heavy quark sector and employed to study the behavior of open-charm and open-bottom mesons. The heavy quark (anti-quark) is treated as frozen and all medium modifications of these bottom-strange mesons are due to their strange anti-quark (quark) content. We observe a pronounced dependence of their medium mass on baryonic density and strangeness content of the medium. Certain aspects of these in-medium interactions are similar to those observed for the strange-charmed mesons in a preceding investigation, such as the lifting of mass-degeneracy of $B_S^0$ and ${\bar B}_S^0$ mesons in hyperonic matter, while the same is respected in vacuum as well as in nuclear matter. In general, however, there is a remarkable distinction between the two species, even though the formalism predicts a completely analogous in-medium interaction Lagrangian density. We discuss in detail the reason for different in-medium behavior of these bottom-strange mesons as compared to charmed-strange mesons, despite the dynamics of the heavy quark being treated as frozen in both cases.

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arXiv2014

CP violation and chiral symmetry breaking in hot and dense quark matter in presence of magnetic field

We investigate chiral symmetry breaking and strong CP violation effects on the phase diagram of strongly interacting matter in presence of a constant magnetic field. The effect of magnetic field and strong CP violating term on the phase structure at finite temperature and density is studied within a three flavor Nambu-Jona-Lasinio (NJL) model including the Kobayashi-Maskawa-t'Hooft (KMT) determinant term. This is investigated using an explicit variational ansatz for ground state with quark anti-quark pairs leading to condensates both in scalar and pseudoscalar channels. Magnetic field enhances the condensate in both the channels. Inverse magnetic catalysis for CP transition at finite chemical potential is seen for zero temperature and for small magnetic fields.

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arXiv2014

Bottomonium states in hot asymmetric strange hadronic matter

We calculate the in-medium masses of the bottomonium states ($Υ(1S)$, $Υ(2S)$, $Υ(3S)$ and $Υ(4S)$) in isospin asymmetric strange hadronic matter at finite temperatures. The medium modifications of the masses arise due to the interaction of these heavy quarkonium states with the gluon condensates of QCD. The gluon condensates in the hot hadronic matter are computed from the medium modification of a scalar dilaton field within a chiral SU(3) model, introduced in the hadronic model to incorporate the broken scale invariance of QCD. There is seen to be drop in the masses of the bottomonium states and mass shifts are observed to be quite considerable at high densities for the excited states. The effects of density, isospin asymmetry, strangeness as well as temperature of the medium on the masses of the $Υ$-states are investigated. The effects of the isospin asymmetry as well as strangeness fraction of the medium are seen to be appreciable at high densities and small temperatures. The density effects are the most dominant medium effects which should have observable consequences in the compressed baryonic matter (CBM) in the heavy ion collision experiments in the future facility at FAIR, GSI. The study of the $Υ$ states will however require access to energies higher than the energy regime planned at CBM experiment. The density effects on the bottomonium masses should also show up in the dilepton spectra at the SPS energies, especially for the excited states for which the mass drop is observed to quite appreciable.

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arXiv2014

Light vector meson masses in strange hadronic matter -- a QCD sum rule approach

We study the properties of the light vector mesons ($ρ$, $ω$ and $ϕ$) in strange hadronic matter using the QCD sum rule approach. The in-medium masses of the vector mesons are calculated from the modifications of the light quark condensates and the gluon condensates in the hadronic medium. The light quark condensates in the hadronic matter are obtained from the values of the non strange and strange scalar fields of the explicit chiral symmetry breaking term in a chiral SU(3) model. The in-medium gluon condensate is calculated through the medium modification of a scalar dilaton field, which is introduced into the chiral SU(3) model to simulate the scale symmetry breaking of QCD. The mass of the $ω$ meson is observed to have initially a drop with increase in density and then a rise due to the scattering with the baryons. The mass of the $ρ$ meson is seen to drop with density due to decrease of the light quark condensates in the medium. The effects of isospin asymmetry and strangeness of the medium on the masses of the vector mesons are also studied in the present work. The $ϕ$ meson is observed to have marginal drop in its mass in the nuclear medium. However, the strangeness of the medium is seen to lead to an appreciable increase in its mass arising due to scattering with the hyperons.

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arXiv2011

D-mesons and charmonium states in hot isospin asymmetric strange hadronic matter

We study the properties of $D$ and $\bar{D}$ mesons in hot isospin asymmetric strange hadronic matter, arising due to their interactions with the hadrons in the hyperonic medium. The interactions of $D$ and $\bar{D}$ mesons with these light hadrons are derived by generalizing the chiral SU(3) model used for the study of hyperonic matter to SU(4). We also study the mass modifications of the charmonium states $J/ψ$, $ψ(3686)$ and $ψ(3770)$ in the isospin asymmetric strange hadronic matter at finite temperatures and investigate the possibility of the decay of the charmonium states into $D\bar D$ pairs in the hot hadronic medium. The mass modifications of these charmonium states arise due to their interaction with the gluon condensates of QCD, simulated by a scalar dilaton field introduced to incorporate the broken scale invariance of QCD within the effective chiral model. We also compute the partial decay widths of the charmonium states to the $D\bar {D}$ pairs in the hadronic medium. The strong dependence on density of the in-medium properties of the $D$, $\bar{D}$ and the charmonium states, as well as the partial decay widths of charmonium states to $D\bar {D}$ pairs, found in the present investigation, will be of direct relevance in observables like open charm enhancement as well as $J/ψ$ suppression in the compressed baryonic matter (CBM) experiments at the future Facility for Antiproton and Ion Research, GSI, where the baryonic matter at high densities is planned to be produced.

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arXiv2011

Strong CP violation and chiral symmetry breaking in hot and dense quark matter

We investigate chiral symmetry breaking and strong CP violation effects in the phase diagram of strongly interacting matter. We demonstrate the effect of strong CP violating terms on the phase structure at finite temperature and densities in a 3-flavor Nambu-Jona-Lasinio (NJL) model including the Kobayashi-Maskawa-t'Hooft (KMT) determinant term. This is investigated using an explicit structure for the ground state in terms of quark-antiquark condensates for both in the scalar and the pseudoscalar channels. CP restoring transition with temperature at zero baryon density is found to be a second order transition at $θ= π$ while the same at finite chemical potential and small temperature turns out to be a first order transition. Within the model, the tri-critical point turns out to be $(T_c,μ_c)\simeq(273,94)$ MeV at $θ= π$ for such a transition.

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arXiv2011

Vacuum structure and chiral symmetry breaking in strong magnetic fields for hot and dense quark matter

We investigate chiral symmetry breaking in strong magnetic fields at finite temperature and densities in a 3 flavor Nambu Jona Lasinio (NJL) model including the Kobayashi Maskawa t-Hooft (KMT) determinant term, using an explicit structure for the ground state in terms of quark antiquark condensates. The mass gap equations are solved self consistently and are used to compute the thermodynamic potential. We also derive the equation of state for strange quark matter in the presence of strong magnetic fields which could be relevant for proto-neutron stars. ~

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arXiv2011

Chiral symmety breaking in 3-flavor Nambu-Jona Lasinio model in magnetic background

Effect of magnetic field on chiral symmetry breaking in a 3-flavor Nambu Jona Lasinio (NJL) model at finite temperature and densities is considered here using an explicit structure of ground state in terms of quark and antiquark condensates. While at zero chemical potential and finite temperature, magnetic field enhances the condensates, at zero temperature, the critical chemical potential decreases with increasing magnetic field.

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arXiv2010

D mesons in isospin asymmetric strange hadronic matter

We study the in-medium properties of $D$ and $\bar{D}$ mesons in isospin asymmetric hyperonic matter arising due to their interactions with the light hadrons. The interactions of $D$ and $\bar{D}$ mesons with these light hadrons are derived by generalizing the chiral SU(3) model used for the study of hyperonic matter to SU(4). The nucleons, the scalar isoscalar meson, $σ$ and the scalar-isovector meson, $δ$ as modified in the strange hadronic matter, modify the masses of $D$ and $\bar{D}$ mesons. It is found that as compared to the $\bar{D}$ mesons, the $D$ meson properties are more sensitive to the isospin asymmetry at high densities. The effects of strangeness in the medium on the properties of $D$ and $\bar{D}$ mesons are studied in the present investigation. The $D$ mesons ($D^0$,$D^+$) are found to undergo larger medium modifications as compared to $\bar{D}$ mesons ($\bar {D^0}$, $D^-$) with the strangeness fraction, $f_s$ and these modifications are observed to be more appreciable at high densities. The present study of the in-medium properties of $D$ and $\bar{D}$ mesons will be of relevance for the experiments in the future Facility for Antiproton and Ion Research, GSI, where the baryonic matter at high densities will be produced. The isospin asymmetric effects in the doublet $D = (D^{0}, D^{+})$ in the strange hadronic matter should show in observables like their production and flow in asymmetric heavy-ion collisions as well as in $J/ψ$ suppression.

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arXiv2010

$J/ψ$ and $η_{c}$ masses in isospin asymmetric hot nuclear matter - a QCD sum rule approach

We study the in-medium masses of the charmonium states $J/ψ$ and $η_{c}$ in the nuclear medium using QCD sum rule approach. These mass modifications arise due to modifications of the scalar and the twist-2 gluon condensates in the hot hadronic matter. The scalar gluon condensate, $<\frac{α_{s}}π G^a_{μν} {G^a}^{μν}>$ and the twist-2 tensorial gluon operator, $<\frac{α_{s}}π G^a_{μσ} {{G^a}_ν}^σ>$ in the nuclear medium are calculated from the medium modification of a scalar dilaton field introduced to incorporate trace anomaly of QCD within the chiral SU(3) model used in the present investigation. The effects of isospin asymmetry, density and temperature of the nuclear medium on the in-medium masses of the lowest charmonium states $J/ψ$ and $η_{c}$ mesons are investigated in the present work. The results of the present investigation are compared with the existing results on the masses of these states. The medium modifications of the masses of these charmonium states ($J/ψ$ and $η_c$) seem to be appreciable at high densities and should modify the experimental observables arising from the compressed baryonic matter produced in asymmetric heavy ion collision experiments at the future facility of FAIR, GSI.

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arXiv2010

$ρ$ - meson spectral function in hot nuclear matter

We study the $ρ$-meson spectral function in hot nuclear matter by taking into account the isospin-symmetric pion and the nucleon loops within the quantum hadrodynamics (QHD) model as well as using an effective chiral SU(3) model. The spectral function of the $ρ$ meson is studied in the mean field approximation (MFA) as well as in the relativistic Hartree (RHA) approximation. The inclusion of the nucleon loop considerably changes the $ρ$-meson spectral function. Due to a larger mass drop of $ ρ$ meson in the RHA, it is seen that the spectral function shifts towards the low invariant mass region, whereas in the MFA the spectral function is seen to be slightly shifted towards the high mass region. Moreover, while the spectral function is observed to be sharper with the nucleon-antinucleon polarization in RHA, the spectral function is seen to be broader in the MFA.

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arXiv2010

D mesons and charmonium states in asymmetric nuclear matter at finite temperatures

We investigate the in-medium masses of $D$ and $\bar{D}$ mesons in the isospin-asymmetric nuclear matter at finite temperatures arising due to the interactions with the nucleons, the scalar isoscalar meson $σ$, and the scalar iso-vector meson $δ$ within a SU(4) model. The in-medium masses of $J/ψ$ and the excited charmonium states ($ψ(3686)$ and $ψ(3770)$) are also calculated in the hot isospin asymmetric nuclear matter in the present investigation. These mass modifications arise due to the interaction of the charmonium states with the gluon condensates of QCD, simulated by a scalar dilaton field introduced to incorporate the broken scale invariance of QCD within the effective chiral model. The change in the mass of $J/ψ$ in the nuclear matter with the density is seen to be rather small, as has been shown in the literature by using various approaches, whereas, the masses of the excited states of charmonium ($ψ(3686)$ and $ψ(3770)$) are seen to have considerable drop at high densities. The present study of the in-medium masses of $D$ ($\bar{D}$) mesons as well as of the charmonium states will be of relevance for the observables from the compressed baryonic matter, like the production and collective flow of the $D$ ($\bar D$) mesons, resulting from the asymmetric heavy ion collision experiments planned at the future facility of the FAIR, GSI. The mass modifications of $D$ and $\bar{D}$ mesons as well as of the charmonium states in hot nuclear medium can modify the decay of the charmonium states ($Ψ^{'}, χ_{c}, J/Ψ$) to $D\bar{D}$ pairs in the hot dense hadronic matter. The small attractive potentials observed for the $\bar{D}$ mesons may lead to formation of the $\bar{D}$ mesic nuclei.

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