arXiv subjects

Amruta Mishra

Publications and source records attributed to Amruta Mishra.

At least 37 records · Page 2Linked to original sources

arXiv2022

In-medium properties of light vector and axial-vector mesons: effects of Dirac sea

The in-medium masses of the light vector, $ρ^{0, \pm}$, $ω$ and the light axial-vector, $A_1^{0, \pm}$ mesons, are studied in the magnetized nuclear matter, accounting for the effects of the Dirac sea. The in-medium partial decay widths for the $A_1\rightarrow ρπ$ channels, are studied from the in-medium masses of the initial and the final state particles, by applying a phenomenological Lagrangian to account for the $A_1ρπ$ interaction vertices. The masses calculated within the QCD sum rule framework, are obtained in terms of the light quark ($\sim \langle \bar{q}q \rangle$) and the scalar gluon condensates ($\sim \langle G^2 \rangle$), as well as the light four-quark condensate ($\sim \langle \bar{q}q\rangle^2 $). The condensates are calculated within the chiral $SU(3)$ model in terms of the medium modified scalar fields. The effects of magnetic fields are incorporated through the Landau energy levels of protons, anomalous magnetic moments (AMMs) of the nucleons in the nuclear matter, in addition to the magnetized Dirac sea contribution, within the chiral effective model. The enhancement (reduction) of the light quark condensates with magnetic field, is called (inverse) magnetic catalysis. The effects of magnetic fields on the in-medium hadronic decay widths of the $A_1$ mesons, are observed to be significant through the Dirac sea effect, accounting for the AMMs of the nucleons. This may affect the light mesons production in the non-central, heavy-ion collision experiments, where estimated magnetic field is very large.

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arXiv2022

Masses of Heavy Quarkonium states in magnetized matter -- effects of PV mixing and (inverse) magnetic catalysis

We study the in-medium masses of the heavy quarkonium (charmonium and bottomonium) states in isospin asymmetric nuclear matter in presence of an external magnetic field. The mass modifications of the heavy quarkonia are obtained from the medium modifications of a scalar dilaton field, $χ$, calculated within a chiral effective model. The dilaton field is introduced in the model through a scale invariance breaking logarithmic potential, and, simulates the gluon condensates of QCD. Within the chiral effective model, the values of the dilaton field along with the scalar (isoscalar, $σ(\sim \langle \bar u u \rangle +\langle \bar d d \rangle)$, isoscalar $ζ(\sim \langle \bar s s \rangle$) and isovector $δ(\sim \langle \bar u u\rangle - \langle\bar d d \rangle)$) fields, are solved from their coupled equations of motion. These are solved accounting for the effects of the Dirac sea (DS) as well as anomalous magnetic moments (AMMs) of the nucleons. The Dirac sea contributions are observed to lead to enhancement (reduction) of the quark condensates (through $σ$ and $ζ$ fields) with increase in magnetic field, an effect called the (inverse) magnetic catalysis. The magnetic field effects on the masses of the heavy quarkonia include the mixing of the pseudoscalar (spin 0) and vector (spin 1) states (PV mixing), as well as, the effects from (inverse) magnetic catalysis. These effects are observed to be significant for large values of the magnetic field. This should have observable consequences on the production of the heavy quarkonia and open heavy flavour mesons, resulting from ultra-relativistic peripheral heavy ion collision experiments, where the created magnetic field can be huge.

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arXiv2022

Open Charm mesons in magnetized nuclear matter -- effects of (inverse) magnetic catalysis

The in-medium masses of the open charm ($D$ and $\bar D$) mesons in magnetized isospin asymmetric nuclear matter are investigated within a chiral effective model, including the contributions of the Dirac sea (DS) to the self-energies of the nucleons. Within the model, the masses of these mesons are calculated from their interactions with the nucleons and the scalar ($σ\sim(\langle\bar u u\rangle+\langle \bar d d \rangle)$, $ζ\sim\langle {\bar s}s\rangle$ and $δ\sim(\langle{\bar u} u\rangle-\langle {\bar d} d\rangle)$) fields. The Dirac sea contributions are observed to lead to an enhancement (reduction) of the quark condensates with increase in magnetic field, an effect called `(inverse) magnetic catalysis'. These contributions are observed to appreciably modify the open charm meson masses calculated within the chiral effective model. In the presence of an external magnetic field, there is mixing of the pseudoscalar and the vector mesons (PV mixing), leading to as a drop (increase) in the mass of the pseudoscalar (longitudinal component of the vector) meson. The effects of the (inverse) magnetic catalysis, in addition to the PV mixing and Landau level contribtuions (for charged mesons) are observed to lead to significant modifications to the masses of the open charm mesons. These can modify the decay widths of the charmonium states to open charm mesons, e.g., $ψ(3770)\rightarrow D\bar D$, as well as $D^*\rightarrow Dπ$ (and $\bar {D^*}\rightarrow {\bar D}π$), which can affect the production of the open charm and charmonium states in ultra relativistic peripheral heavy ion collision experiments, where the created magnetic field is huge.

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arXiv2022

Upsilon decay widths in magnetized asymmetric nuclear matter

The in-medium partial decay widths of $Υ(4S) \rightarrow B\bar B$ in magnetized asymmetric nuclear matter are studied using a field theoretic model for composite hadrons with quark (and antiquark) constituents. The medium modifications of the decay widths of $Υ(4S)$ to $B\bar B$ pair in magnetized matter arise due to the mass modifications of the decaying $Υ(4S)$ as well as of the produced $B$ and $\bar B$ mesons. The in-medium masses of the open bottom meson in magnetized nuclear matter are computed from their interactions with the nucleons and the scalar mesons within a chiral effective model. The mass modification of the $Υ(4S)$ arises due to the medium modification of a scalar dilaton field, which is introduced in the model to simulate the gluon condensates of QCD. The charged $B^{\pm}$ mesons have additional contributions from the Landau energy levels, leading to positive shifts in their masses in the presence of a magnetic field. In the presence of an external magnetic field, there are contributions to the masses of the $B$, $\bar B$ mesons and $Υ(4S)$ state (longitudinal component) due to the pseudoscalar meson-vector meson (PV) mixing ($B-B^*$, $\bar B- \bar {B^*}$ and $Υ(4S)-η_b(4S)$ mixings), which are also considered in the present study. The PV mixing effects are observed to be the dominant contributions to the mass shifts of these mesons, which lead to appreciable modifications in the decay widths of $Υ(4S)$ to the neutral ($B^0 \bar {B^0}$) and the charged ($B^+ B^-$) pairs in the presence of a magnetic field. These should have observable consequence in the production of open bottom mesons and bottomonium states at LHC and RHIC, where huge magnetic fields are produced in ultra-relativistic peripheral heavy ion collisions.

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arXiv2022

Open Bottom Mesons and Upsilon States in Hot Magnetized Strange Hadronic Matter

The masses of open bottom mesons ($B$($B^+$,$B^0$), $\bar{B}$($B^-$,$\bar{B^0}$), $B_s$(${B_{s}}^0$, $\bar{{B_s}^0}$)) and upsilon states ($Υ(1S)$, $Υ(2S)$, $Υ(3S)$, $Υ(4S)$, and $Υ(1D)$) are investigated in the isospin asymmetric strange hadronic medium at finite temperature in the presence of strong magnetic fields using a chiral effective Lagrangian approach. For charged baryons, the magnetic field introduces contribution from Landau energy levels. The masses of the open bottom mesons get modified through their interactions with the baryons and the scalar mesons, which undergo modifications in a magnetized medium. The charged open bottom mesons have additional positive mass shifts due to Landau quantization in the presence of the magnetic field. The medium mass shift of the upsilon states originates from the modification of the gluon condensates simulated by the variation of dilaton field ($χ$) and a quark mass term in the magnetized medium. The open bottom mesons and upsilon states experience a mass drop in the magnetized medium. The masses of these mesons initially increase with a rise in temperature, and beyond a high value of temperature, their masses are observed to drop. When the temperature is below 90 MeV, the in-medium masses of the mesons increase with an increase in the magnetic field. However, at high temperatures (T $>$ 90 MeV), the masses are observed to drop with an increase in the magnetic field. The dominant in-medium effects are the density effects, which can have observable effects in asymmetric heavy-ion collisions planned at compressed baryonic matter experiments at FAIR at the future facility of GSI.

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arXiv2021

Open charm and charmonium states in strong magnetic fields

The mass modifications of the open charm ($D$ and $D^*$) mesons, and their effects on the decay widths $D^*\rightarrow Dπ$ as well as of the charmonium state, $Ψ(3770)$ to open charm mesons ($Ψ(3770)\rightarrow D\bar D$), are investigated in the presence of strong magnetic fields. These are studied accounting for the mixing of the pseudoscalar ($P$) and vector ($V$) mesons ($D-D^*$, $η_c'-Ψ(3770)$ mixings), with the mixing parameter, $g_{PV}$ of a phenomenological three-point ($PVγ$) vertex interaction determined from the observed radiative decay width of $V\rightarrow Pγ$. For charged $D-D^*$ mixing, this parameter is dependent on the magnetic field, because of the Landau level contributions to the vacuum masses of these mesons. The masses of the charged $D$ and $D^*$ mesons modified due to $PV$ mixing, in addition, have contributions from the lowest Landau levels in the presence of a strong magnetic field. The effects of the magnetic field on the decay widths are studied using a field theoretic model of composite hadrons with quark (and antiquark) consittuents. The parameter for the charged $D-D^*$ mixing is observed to increase appreciably with increase in the magnetic field. This leads to dominant modifications to their masses, and hence the decay widths of charged $D^*\rightarrow Dπ$ as well as $Ψ(3770)\rightarrow D^+D^-$ at large values of the magnetic field. The modifications of the masses and decay widths of the open and hidden charm mesons in the presence of strong magnetic fields should have observable consequences on the production of the open charm ($D$ and $D^*$) mesons as well as of the charmonium states resulting from non-central ultrarelativistic heavy ion collision experiments.

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arXiv2021

Strange mesons in strong magnetic fields

The masses of the strange mesons ($K$, $K^*$ and $ϕ$) are investigated in the presence of strong magnetic fields. The changes in the masses of these mesons arise from the mixing of the pseusdoscalar and vector mesons in the presence of a magnetic field. For the charged mesons, these mass modifications are in addition to the contributions from the lowest Landau energy levels to their masses. The decay widths, $ϕ\rightarrow K\bar K$ and $K^* \rightarrow Kπ$, in the presence of the magnetic field are studied using a field theoretic model of composite hadrons with constituent quarks/antiquarks. The model uses the free Dirac Hamiltonian in terms of the constituent quark fields as the light quark antiquark pair creation term and explicit constructions for the meson states in terms of the constituent quarks and anitiquarks to study the decay processes. The study of the masses and decay widths of the strange mesons in strong magnetic fields can have observable consequences on the production of the open and hidden strange mesons in the peripheral ultra high energy collisions at LHC, where the created magnetic field can be huge.

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arXiv2021

Spectral functions of strange vector mesons in asymmetric hyperonic matter

We study the medium modifications of the spectral functions as well as production cross-sections of the strange vector mesons ($ϕ$, $K^*$ and $\bar {K^*}$) in isospin asymmetric strange hadronic matter. These are obtained from the in-medium masses of the open strange mesons and the decay widths $ϕ\rightarrow K\bar K$, $K^* \rightarrow Kπ$ and $\bar {K^*} \rightarrow {\bar K}π$ in the hadronic medium. The decay widths are computed using a field theoretic model of composite hadrons with quark/antiquark constituents, from the matrix element of the light quark-antiquark pair creation term of the free Dirac Hamiltonian between the initial and final states. The matrix element is multiplied with a coupling strength parameter for the light quark-antiquark pair creation, which is fitted to the observed vacuum decay width of the decay process. There are observed to be substantial modifications of the spectral functions as well as production cross-sections of these vector mesons due to isospin asymmetry as well as strangeness of the hadronic medum at high densities. These studies should have observable consequences, e.g. in the yield of the hidden and open strange mesons arising from the isospin asymmetric high energy heavy ion collisions at the Compressed baryonic matter (CBM) experiments at the future facility at GSI.

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arXiv2021

QCD sum rule analysis of Bottomonium ground states

The in-medium masses of the bottomonium ground states [$1S$ ($Υ(1S), η_b$) and $1P$ ($χ_{b0},χ_{b1}$)] are investigated in the magnetized vacuum (nuclear medium), using the QCD sum rule framework. In QCD sum rule approach, the mass modifications are calculated in terms of the medium modifications of the scalar and twist-2 gluon condensates, which are obtained in the nuclear medium, from the medium change of a scalar dilaton field, $χ$ within a chiral effective model. The in-medium masses of the bottomonium ground states are observed to decrease with increasing density. P-wave states are observed to have more appreciable mass-shifts than the S-wave states. In the present investigation, the effects of spin-mixing between 1S bottomonium states, $Υ(1S)$ and $η_b$ are taking into account in presence of an external magnetic field. The contribution of magnetic fields are seen to be dominant via spin-magnetic field interaction effects, which leads to an appreciable rise and drop in the in-medium masses of the longitudinal component of vector $1S$ state ($Υ$) and pseudoscalar state ($η_b$) respectively. For zero magnetic field, the effects of baryon density on the bottomonium ground states in isospin asymmetric nuclear medium are observed to be quite appreciable. These should have observable consequences for the production of the open and hidden bottom meson states resulting from high energy asymmetric nuclear collisions in facilities which probe high density baryonic matter. There is observed to be large contributions to the masses of the longitudinal component of the vector bottomonium state, $Υ(1S)$ and pesudoscalar state $η_b$ in strong magnetic fields.

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arXiv2021

Open charm mesons and Charmonia in magnetized strange hadronic matter

We investigate the in-medium masses of open charm mesons ($D$($D^0$, $D^+$), $\bar{D}$($\bar{D^0}$, $D^-$), $D_s$(${D_{s}}^+$, ${D_{s}}^-$)) and charmonium states ($J/ψ$, $ψ(3686)$, $ψ(3770)$, $χ_{c0}$, $χ_{c2}$) in strongly magnetized isospin asymmetric strange hadronic matter using a chiral effective model. In the presence of the magnetic field, the number density and scalar density of charged baryons have contributions from Landau energy levels. The mass modifications of open charm mesons arise due to their interactions with nucleons, hyperons, and the scalar fields (the non-strange field $σ$, strange field $ζ$ and isovector field $δ$) in the presence of the magnetic field. The mass modifications of the charmonium states arise from the variation of dilaton field ($χ$) in the magnetized medium, which simulates the gluon condensates of QCD. The in-medium mass of open charm mesons and charmonia are observed to decrease with an increase in baryon density, whereas the charged $D^+$, $D^-$, ${D_{s}}^+$ and ${D_{s}}^-$ mesons have additional positive mass shifts due to Landau quantization in the presence of the magnetic field. The effects of strangeness fraction are found to be more dominant for the $\bar{D}$ mesons as compared to the $D$ mesons. The mass shifts of charmonia are observed to be larger in hyperonic medium compared to the nuclear medium.

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arXiv2020

Masses and Decay widths of Charmonium states in presence of strong magnetic fields

The masses and decay widths of charmonium states are studied in the presence of strong magnetic fields. The mixing between the pseudoscalar and vector charmonium states at rest is observed to lead to appreciable negative (positive) shifts in the masses of the pseudoscalar (longitudinal component of the vector) charmonium states in vacuum/hadronic medium in the presence of high magnetic fields. The pseudoscalar and vector charmonium masses in the hadronic medium, calculated in an effective chiral model from the medium changes of a scalar dilaton field, have additional significant modifications due to the mixing effects. The masses of the $D$ and $\bar D$ mesons in the magnetized hadronic matter are calculated within the chiral effective model. The partial decay widths of the vector charmonium state to $D\bar D$ are computed using a field theoretical model for composite hadrons with quark/antiquark constituents, and are compared to the decay widths calculated using an effective hadronic Lagrangian. The effects of the mixing are observed to lead to significant contributions to the masses of the pseusoscalar and vector charmonium states, and an appreciable increase in the decay width $ψ(3770) \rightarrow D\bar D$ at large values of the magnetic fields. These studies of the charmonium states in strong magnetic fields should have observable consequences on the dilepton spectra, as well as on the production of the open charm mesons and the charmonium states in ultra relativistic heavy ion collision experiments.

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arXiv2019

Charmonia decay widths in magnetized matter using a model for composite hadrons

The decay widths of the charmonium states to $D\bar D$ in isospin asymmetric nuclear matter in the presence of a magnetic field are studied, using a field theoretical model for composite hadrons with quark/antiquark constituents. The medium modifications of these partial decay widths arise due to the changes in the masses of the decaying charmonium state and the produced $D$ and $\bar D$ mesons in the magnetized hadronic matter, calculated within a chiral effective model. The decay widths are computed using the light quark--antiquark pair creation term of the free Dirac Hamiltonian in terms of the constituent quark field operators. The results of the present investigation are compared with the in-medium decay widths obtained within the $^3P_0$ model. Within the $^3P_0$ model, the charmonium decay widths are calculated using the creation of a light quark--antiquark pair in the $^3P_0$ state. In the presence of a magnetic field, the Landau level contributions give rise to positive shifts in the masses of the charged $D$ and $\bar D$ mesons. This leads to the decay of charmonium to the charged $D^+ D^-$ to be suppressed as compared to the neutral $D\bar D$ pair in symmetric nuclear matter, whereas in asymmetric nuclear matter, the larger mass drop of the $D^+D^-$ pair, as compared to the $D^0 \bar {D^0}$ pair leads to the production of charged open charm meson pairs to be enhanced as compared to the charmonium decay channel to $D^0 {\bar {D^0}}$.

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arXiv2019

Charmonium ground states in presence of strong magnetic fields

The in-medium masses of the lowest S-wave charmonium states (vector meson, $J/ψ$ and pseudoscalar meson, $η_c$) and P-wave charmonium states (scalar, $χ_{c0}$ and axialvector $χ_{c1}$) are investigated in magnetized nuclear matter, within the framework of QCD sum rule approach. These are computed from the medium modifications of the scalar as well as twist--2 gluon condensates, obtained from the medium modifications of a scalar dilaton field, within a chiral effective model. The effects of the magnetic field, isospin asymmetry and density on the masses of these charmonium states have been investigated. The modifications of the masses of the P-wave charmonium states ($χ_{c0}$ and $χ_{c1}$) are observed to be much larger as compared to those of the S-wave states, $J/ψ$ and $η_c$ within the QCD sum rule approach. The effects of the coupling of the spin with the magnetic field are also investigated in the present work, which result in the mixing of the spin zero charmonium state with the longitudinal component of the vector meson. This leads to an increase (drop) in mass of the longitudinal $J/ψ$ ($η_c$) for the S-wave states. The effects of the spin-magnetic field interactions are observed to be dominant at high magnetic fields.

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arXiv2019

Light vector mesons ($ω$, $ρ$ and $ϕ$) in strong magnetic fields: A QCD sum rule approach

The mass modifications of the light vector mesons ($ω$, $ρ$ and $ϕ$) are investigated in asymmetric nuclear matter in the presence of strong magnetic fields, using a QCD sum rule approach. These are computed from the medium modifications of the non-strange and strange light quark condensates as well as scalar gluon condensate. The quark and gluon condensates are calculated from the medium changes of the scalar fields (non-strange and strange) and a scalar dilaton field in the magnetized nuclear matter, within a chiral SU(3) model. The scalar dilaton field within the model breaks the scale invariance of QCD and simulates the gluon condensate. The anomalous magnetic moments for the nucleons are taken into account in the present study.

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arXiv2019

Charmonium decay widths in magnetized matter

We study the partial decay widths of the charmonium states ($J/ψ$, $ψ(3686)$, $ψ(3770)$, $χ_{c0}$, $χ_{c2}$) to $D\bar D$ ($D^+D^-$ or $D^0\bar {D^0}$) in isospin asymmetric nuclear matter, in the presence of strong magnetic fields. The in-medium partial decay widths of charmonium states to $D\bar D$ are calculated within a light quark--antiquark pair creation model, namely the $^3P_0$ model, using the in--medium masses of the charmonia as well as $D$ and $\bar D$ mesons in the magnetized nuclear matter obtained within a chiral effective model. The presence of a magnetic field leads to Landau quantization of the energy levels of the proton in the nuclear medium. The effects of magnetic field and isospin asymmetry on the charmonium decay widths to $D\bar D$ are found to be quite prominent. The effects of the anomalous magnetic moments have also been taken into consideration for obtaining the in-medium masses of these heavy flavour mesons, used to calculate the partial decay widths of the charmonium states. The medium modifications of the charmonium decay widths can have observable consequences on the production of the charmed mesons in high energy asymmetric heavy ion collision experiments.

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arXiv2019

Kaons and antikaons in strong magnetic fields

The in-medium masses of the kaons and antikaons in strongly magnetized asymmetric nuclear matter are studied using a chiral SU(3) model. The medium modifications of the masses of these open strange pseudoscalar mesons arise due to their interactions with the nucleons and scalar mesons within the model. The proton, the charged nucleon, has effects from the Landau energy levels in the presence of the magnetic field. The anomalous magnetic moments (AMM) of the nucleons are taken into consideration in the present study and these are seen to be large at high magnetic fields and high densities. The isospin effects are appreciable at high densities. The density effects are observed to be the dominant medium effects, as compared to the effects from magnetic field and isospin asymmetry. ~

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arXiv2018

Charmonium states in strong magnetic fields

The medium modifications of the masses of the charmonium states (J/$ψ$, $ψ$(3686) and $ψ$(3770)) in asymmetric nuclear matter in the presence of strong magnetic fields are studied using an effective chiral model. The mass modifications arise due to medium modifications of the scalar dilaton field, which simulates the gluon condensates of QCD within the effective hadronic model. The effects due to the magnetic field as well as isospin asymmetry are observed to be appreciable at high densities for the charmonium states, which can have consequences, e,g, in the production of the open charm mesons and the charmonium states, in the asymmetric heavy ion collisions at the compressed baryonic matter (CBM) experiments at the future facility at GSI. The presence of magnetic field leads to Landau quantization of the energy levels of the proton in the asymmetric nuclear matter. The effects of the anomalous magnetic moments of the proton and neutron on the masses of the charmonium states are studied and are observed to lead to larger masses of the charmonium states, as compared to when these effects are not taken into account.

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arXiv2018

Upsilon states in magnetized nuclear matter

The mass modifications of the bottomonium states ($Υ(NS)$,$N=1,2,3,4$ and $Υ(1D)$) in magnetized nuclear matter are studied using chiral effective model. The in-medium masses are calculated from the medium modification of the scalar dilaton field in the chiral effective model, which simulates the gluon condensates of QCD. The strengths of the wave functions (assumed to be harmonic oscillator wave functions) denoted by the parameter, $β$, of the $Υ(NS)$, $N=1,2,3,4$, are fitted from their observed decay widths to $e^+e^-$. The decay width for the channel, $Υ(1D) \rightarrow e^+ e^-$ %, which has not yet been observed experimentally, has been predicted in the present work, by using the value of the parameter, $β$ for $Υ(1D)$, interpolated from the $β$ versus mass relation, for the upsilon states. The effects of the isospin asymmetry of the nuclear medium on the masses of the upsilon states are investigated and are observed to be large for high densities. This should have observable consequences at the asymmetric heavy ion collisions at the Compressed baryonic matter (CBM) experiments at FAIR, GSI as well as at SPS, CERN. The study of the bottomonium states at CBM will however require access to higher energies than the energy regime planned at present. The effects of magnetic field on the masses of bottomonium states in nuclear matter are studied in the present work. These masses are investigated including the anomalous magnetic moments (AMM) of the nucleons, and compared to the results when the AMMs of nucleons are not taken into account. The effects of magnetic field as well as isospin asymmetry on the upsilon masses are obserevd to be large at high densities.

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