arXiv subjects

R. N. Panda

Publications and source records attributed to R. N. Panda.

At least 19 recordsLinked to original sources

arXiv2026

Universality in spacetime $\omega$ modes of quarkyonic stars

The gravitational wave $\omega$ mode spectrum presents a unique window into the dense interior of neutron stars, probing physics inaccessible to electromagnetic observations. This work investigates the $\omega$ modes of compact stars composed of quarkyonic matter. The quarkyonic model, which describes a cross-over transition between nucleonic and quark matter treated as quasi-particles, is formulated within the Relativistic Mean-Field (RMF) theory using the G3 and IOPB-I parameterizations. This core is surrounded by a mantle of hadronic matter, creating a multicomponent stellar interior. The overall Equation of State (EOS) is governed by two key parameters: the transition density ($n_t$), the QCD confinement scale ($\Lambda_{\rm cs}$), which are varied to construct models consistent with current astrophysical constraints on mass and radius. We compute the complex eigenfrequencies (damped oscillations) of the fundamental and first excited $\omega$ modes using the phase-amplitude method within a full general relativistic framework. Our simulations reveal that the admixed quarkyonic structure produces a unique $\omega$ mode signature, distinctly different from pure hadronic or hybrid stars. The spectrum exhibits a strong, degenerate dependence on the EOS, where the stiffening effect of the quarkyonic matter influences oscillation frequencies and damping times in a characteristic manner. We also demonstrate that $\omega$ mode frequencies for quarkyonic stars follow approximate universal relations, largely independent of the EOS.

astro-ph.HE↗

arXiv2025

An $A_4$-Symmetric Double Seesaw for Neutrino Masses and Mixing in Light of JUNO results

We discuss a double seesaw mechanism for generating light neutrino masses within the Standard Model extensions that include both right-handed neutrinos and extra gauge-singlet sterile fermions. The flavour structure of the double seesaw framework is invoked by an $A_4$ discrete symmetry which yields predictive textures for the Dirac neutrino mass matrix $M_D$, the mixing matrix $M_{RS}$ connecting right-handed and sterile neutrinos, and the bare Majorana mass matrix $M_S$ for the sterile neutrinos. The interesting feature of the present framework is that the combination of the double seesaw mechanism and $A_4$ flavour alignments yields a leading-order TBM structure, corrected by a single rotation in the (1-3) sector. We also derive analytic expressions for the heavy sterile eigenvalues and for the resulting light neutrino masses, thereby clarifying the role of the symmetry in shaping the neutrino mass hierarchy. We further incorporate the most recent JUNO measurements, which improve the precision of the solar mixing angle $\sin^2\theta_{12} \simeq 0.31$, along with updated constraints on $\sin^2\theta_{13}$. We show that these results significantly restrict the allowed parameter space of the model. In particular, the observed value of $\sin^2\theta_{12}$ constrains the magnitude of the (1--3) rotation and the phases associated with the $A_4$ flavon couplings, while the value of $\sin^2\theta_{13}$ sharpens these restrictions further. Overall, the interplay between double seesaw dynamics, $A_4$ flavour symmetry, and the recent JUNO constraints yields a highly predictive framework for neutrino masses and mixings, offering a coherent explanation for the generation of light neutrino masses and testable predictions for future experiments.

hep-ph↗

arXiv2025

Core or Halo? Two-Fluid Analysis of Dark Matter-Admixed Quarkyonic Stars in the Multi-Messenger Era

For the first time, we explore dark matter (DM) admixed quarkyonic stars (DAQSs) within a two-fluid formalism, where the normal/visible sector is modeled by a quarkyonic equation of state (EOS) in the Effective Relativistic Mean Field (E-RMF) framework and the DM component is treated as a degenerate fermionic gas with scalar and vector self-interactions. Our analysis begins with the mass-radius (M-R) relation, showing that the inclusion of DM enables stellar configurations to reach the mass range compatible with the GW190814 event. We identify both DM core and DM halo morphologies among the viable EOSs, with core dominated and halo dominated cases exhibiting distinct signatures. By fixing the stellar mass within the GW190814 range, we constrain the possible dark matter fractions and explore the role of different interaction channels. Using the EOSs consistent with these constraints, we further investigate the tidal deformability ($\Lambda$), moment of inertia (MOI), and stellar radius, finding broad agreement with constraints from GW170817, GW190814, and NICER. Finally, we compile the characteristic properties of DAQSs, including EOS type, DM fractions, morphology (core vs halo), and macroscopic observables in a comparative summary. This study provides a unified two-fluid framework to explore dense QCD matter and dark matter in the multi-messenger era, suggesting that the GW190814 secondary object could plausibly be interpreted as either a DM core or a DM halo quarkyonic star.

astro-ph.HE↗

arXiv2025

$w$-mode oscillation of neutron star in a new relativistic hybrid model

We investigate how the pulsation frequencies of axial gravitational-wave modes ($w$-modes) in a non-rotating neutron star depend on its composition, particularly when including quarkyonic matter and fermionic dark matter. These modes emerge from the coupling between the star's fluid component and the gravitational field of general relativity, which are highly damped and characterized by complex frequencies with comparable real and imaginary parts. Using a relativistic mean field formalism for the nucleonic component, we modeled the neutron star's interior, while the exterior is analyzed through the complex-coordinate method to determine the $w$-modes. Our study employs a realistic equation of state, based on different physical assumptions and covering a broad area of observational constraints, starting from finite nuclei to nuclear matter with extreme conditions. The numerical findings demonstrate that axial $w$-modes provide valuable insights into the properties of neutron star matter, highlighting their significance in probing the star's internal structure.

astro-ph.HE↗

arXiv2025

Anomalous Behavior of Giant Monopole Resonance Energy with Nuclear Matter Incompressibility in the framework of Relativistic Mean Field Formalism and Coherent Density Fluctuation Model

The finite nucleus incompressibility $K^A$ is evaluated using the coherent density fluctuation model with the extended relativistic mean field density. The relativistic energy density functional for nuclear matter is replaced by the local density approximation for finite nuclei. The equation is used to calculate the finite nuclear incompressibility, which is further utilized to evaluate the isoscalar giant monopole excitation (ISGMR) energy $E_M$. This excitation energy is compared with other theoretical calculations and experimental data, wherever available. The results are comparable to the data. In contrast to the general understanding, the $E_M$ of finite nucleus is found to be maximum for the lowest nuclear matter incompressibility $K_{\infty}$, whereas it is minimum for the maximum $K_{\infty}$. These reverse results may be due to the self- and cross-interactions of the vector mesons in the nuclear potential.

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arXiv2025

Exploring the giant monopole resonance in superheavy nuclei: A theoretical perspective

Within the relativistic mean field framework, in an extended Thomas-Fermi approximation, we calculate the binding energy and charge distribution radius for the latest superheavy nuclei, synthesised in various laboratories, with atomic numbers $Z = 110-118$. The binding energy and radii are compared with the results obtained from relativistic Hartree calculations along with the experimental data, wherever available, to check the reliability of the methods. The calculations are extended to estimate the giant monopole resonances to understand the collective vibration of the nucleons for such superheavy nuclei. The giant monopole resonances obtained from scaling calculations are compared with the constraint computations. Furthermore, the results are compared with other known methods, such as the relativistic Random Phase Approximation (RPA) and time-dependent mean field calculations, along with some known lighter nuclei, specifically Zr isotopes (N = 42-86) and O isotopes (N = 10-36). Finally, the nuclear compressibility of the superheavy nuclei is predicted from the energy obtained in the breathing mode.

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arXiv2025

Superheavy Nuclei and the Changing Face of Nuclear Magicity

Using a relativistic mean field formalism, we analyzed the magic number sequence for finite nuclei in the superheavy valley. The result for the IOPB-I parameter set is compared with the well-known NL3 force. The magic numbers obtained from IOPB-I and NL3 interactions are found to be similar. Analysing the single-particle levels and the number of nucleons occupied in it, we find the close shell sequence as 2, 8, 18, 34, 50, 58, 80, 82, 92, 114, 120, 120, 138, 164, 172, 184 and 198 for the $^{318}{120}$ mass region. Again, with a careful inspection, we noticed large shell gaps at nucleon numbers 2, 8, 18, 34, 50, 58, 80, 92, 120, 138, 164, 172, 184, and 198, which may be considered as the magic number sequence for the superheavy nuclei. This change may be due to the shape change of the nuclear potential as compared to the stability valley.

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arXiv2025

Dark Matter Effects on the Curvature of Neutron Stars within the new Quarkyonic Model Coupled with Relativistic Mean Field Theory

For the first time, we analyze the impact of dark matter (DM) on the curvature properties of quarkyonic neutron stars (NS) using a hybrid model based on quarkyonic-effective field theory within the relativistic mean-field (E-RMF) framework. This study examines the radial variation of curvature components, including the Ricci scalar ($\cal{R}$), Ricci tensor ($\cal{J}$), Kretschmann scalar ($\cal{K}$), and Weyl tensor ($\cal{W}$), under different DM admixtures. These components offer critical insights into the spacetime geometry and gravitational field strength within the star. The analysis spans canonical mass (1.4 $M_{\odot}$) and maximum mass configurations, varying key parameters such as the transition density ($n_t$) and QCD confinement scale ($\Lambda_{\rm cs}$), which influence matter transitions and quark confinement. Our results reveal that DM and quarkyonic matter (QM) significantly affect the star's curvature. Central curvature values, particularly $\cal{R}$, $\cal{J}$, and $\cal{K}$, increase with DM due to higher central densities but decrease with stronger QM effects. Stiffer EOSs yield smoother curvature profiles, while softer EOSs influenced by DM redistribute curvature more dynamically. DM softens the EOS, reducing central pressure and compactness, whereas higher $n_t$ values enhance compactness and central pressures. These findings show that dark matter plays a key role in shaping the curvature of quarkyonic neutron stars, offering new insights into compact objects with exotic matter.

astro-ph.HE↗

arXiv2024

$f$-mode oscillations of dark matter admixed quarkyonic neutron star

We systematically investigate $f-$mode oscillations ($\ell$ = 2) in quarkyonic neutron stars with dark matter, employing the Cowling approximation within the framework of linearized general relativity. The relativistic mean-field approach is used to compute various macroscopic properties of neutron stars. The analysis focuses on three key free parameters in the model: transition density, QCD confinement scale, and dark matter (DM) Fermi momentum, all of which significantly affect the properties of $f-$mode oscillations. The inclusion of dark matter in quarkyonic equations of state leads to notable variations in $f-$mode frequencies. Despite these changes, several universal relations among the oscillation properties are found to hold, demonstrating their robustness in the presence of dark matter.

astro-ph.HE↗

arXiv2024

Exploring the impact of $\Delta$-isobars on Neutron Star

We include the $\Delta$-isobars in the equation of state (EOS) of neutron star (NS) and study its effects with various parameter sets of the RMF model. We compare our results with the NS's constraints from the mass-radius measurement of PSR J0348+0432, PSR J1614-2230, PSR J0030+0451, PSR J0740+6620, PSR J0952-0607, and tidal deformability of GW170817. We calculate the mass-radius profile and tidal deformabilities of the NS using 21 parameter sets of the RMF model.Analyzing the result with various parameters, it is clear that only few parameter sets can satisfy simultaneously the constraints from NICER and GW170817. NLD parameter set satisfy all the constraints of NICER and GW170817. For its strong predictive power for the bulk properties of the neutron star, we take NLD parameter set as a representative for the detailed calculation of effect of $\Delta$-isobar on neutron star properties. We demonstrate that it is possible that $\Delta$-isobar can produce at 2-3 times the saturation density by adjusting the coupling constants $X_{\sigma\Delta}$, $X_{\rho\Delta}$ and $X_{\omega\Delta}$ in an appropriate range. Bulk properties of the NS like mass-radius profile and tidal deformability is strongly affected by the interaction strength of $\Delta$-isobar. Our calculation shows that it is also possible that by choosing $X_{\sigma\Delta}$, $X_{\rho\Delta}$ and $X_{\omega\Delta}$ to a suitable range the threshold density of $\Delta^-$-isobar become lower than $\Lambda^0$ hyperon. For a particular value of $\Delta$-coupling constants, the $R_{1.4}$ decrease by 1.7 km. This manuscipt give an argumentative justification for allowing $\Delta$-isobar degrees of freedom in the calculation of the NS properties.

nucl-th↗

arXiv2024

Exclusive rare semileptonic decays of $B$ and $B_c$ mesons in the relativistic independent quark model

We investigate the exclusive rare semileptonic decays: $B(B_c)\to K(D_{(s)})l\bar{l}/\Sigma\nu_l\bar{\nu_l}$ ($l=\mu, \tau$) in the framework of relativistic independent quark (RIQ) model based on an average flavor independent confining potential in equally mixed scalar-vector harmonic form. The invariant weak form factors, parametrising the matrix elements between participating meson states are calculated in the parent meson rest frame. The momentum transfer dependence of the form factors is reliably determined in the whole accessible kinematical range: $q^2_{min}\leq 0\leq q^2_{max}$. Our predicted branching fractions for $B\to K\mu^+\mu^-/\tau^+\tau^-(\Sigma\nu_l\bar{\nu_l})$, $B_c\to D(D_s)\mu^+\mu^-$, $B_c\to D(D_s)\tau^+\tau^-$ and $B_c\to D(D_s)\Sigma\nu_l\bar{\nu_l}$, obtained in order of $10^{-7}(10^{-6})$, $10^{-9}(10^{-7})$, $10^{-9}(10^{-8})$ and $10^{-8}(10^{-7})$, respectively are in reasonable agreement with other Standard Model predictions and Lattice QCD results. The averaged values of the lepton polarization asymmetries for decay modes are obtained as $\langle P_L(B\to K\mu^+\mu^-)\rangle$=-0.97, $\langle P_L(B_c\to D_{(s)}\mu^+\mu^-)\rangle$=-0.972, $\langle P_L(B\to K\tau^+\tau^-)\rangle$=-0.224, $\langle P_L(B_c\to D\tau^+\tau^-)\rangle$=-0.275 and $\langle P_L(B_c\to D_s\tau^+\tau^-)\rangle$=-0.194.

hep-ph↗

arXiv2024

Purely leptonic decays of heavy-flavored charged mesons

We study the purely leptonic decays of heavy-flavored charged pseudoscalar (P) and vector (V) mesons ($D_{(s)}^{(*)+}$, $B_{(c)}^{(*)+}$) in the relativistic independent quark (RIQ) model based on an average flavor-independent confining potential in equally mixed scalar-vector harmonic form. We first compute the mass spectra of the ground-state-mesons and fix the model parameters necessary for the present analysis. Using the meson wave functions derivable in the RIQ model, and model parameters so fixed from hadron spectroscopy, we predict the decay constants: $f_{P(V)}$, ratios of decay constants: $f_{V}/f_{P}$, $f_{P_1}/f_{P_2}$, $f_{V_1}/f_{V_2}$, and the branching fractions (BFs): ${\cal B}(P(V)\to l^+ν_l)$, $l=e, μ, τ$, which agree with the available experimental data and other Standard Model (SM) predictions. For the unmeasured decay constants especially in the purely leptonic decays of the charged vector mesons, our predictions could be tested in the upcoming Belle-II, SCTF, CEPC, FCC-ee and LHCb experiments in near future.

hep-ph↗

arXiv2024

Dark Matter Influence on Quarkyonic Stars: A Relativistic Mean Field Analysis

The formulation of quarkyonic matter consists of treating both quarks and nucleons as quasi-particles, where a cross-over transition occurs between the two phases. This work is based upon some of the early ideas of quark matter. It can satisfy the different observational constraints on the neutron star (NS), such as its maximum mass and the canonical radius. In addition, we put an extra component inside the NS known as Dark Matter (DM) because it is trapped due to its immense gravitational potential. In this work, we explore the impact of fermionic DM on the structure of the NS. The equation of state (EOS) is derived for the NS with the quarkyonic matter by assuming that nucleons and quarks are in equilibrium, followed by the relativistic mean-field (RMF) formalism. The recently modeled two parameterizations, such as G3 and IOPB-I, are taken to calculate the various macroscopic properties of the NS. The three unknown parameters such as the transition density ($n_t$), the QCD confinement scale ($\Lambda_{\rm sc}$), and the DM Fermi momentum ($k_f^{\rm DM}$) are varied to obtain the NS properties. The quarkyonic matter stiffens the EOS while DM softens it. The mutual combination provides us with good theoretical predictions for the magnitude of macroscopic properties consistent with the different observational results. Also, one can estimate the parameters of the DM admixed quarkyonic star with different statistical analyses, which can be further used to explore the other properties of the quarkyonic star.

astro-ph.HE↗

arXiv2022

Correlation between the nuclear structure and reaction dynamics of Ar-isotopes as projectile using the relativistic mean-field approach

This theoretical study is devoted to bridging the gap between the nuclear structure and reaction dynamics and unravelling their impact on each other, considering the neutron-rich light mass 30-60Ar isotopes. Using the relativistic mean-field with the NL3* parameter set, several bulk properties such as binding energies, charge radii, quadrupole deformation parameter, two neutron separation energy, and differential two neutron separation energy with the shell closure parameter are probed for the mentioned isotopic chain. For validation, the RMF (NL3*) results are compared with those obtained from the finite range droplet model (FRDM), Weizsacker-Skyrme model with WS3, WS* parameters and the available experimental data. Most of the participating isotopes are found to be prolate in structure and neutron shell closures are conspicuously revealed at N=14, 20, 40 but weakly shown at N=24, 28, 34. From our analysis, a central depletion in the nucleonic density is identified in 32Ar and 42-58Ar, indicating them as possible candidates for a semi-bubble-like structure. Interestingly, these results are consistent with recent theoretical and experimentally measured data. Besides, using the Glauber model, the reaction cross-sections are determined by taking 26-48Ar as projectiles and stable targets such as 12C, 16O, 40Ca, 90Zr, 124,132Sn, 208Pb and 304120. Although there is no experimental evidence for the stability of 304120, it has been predicted in Ref. [Mod. Phys. Lett. A {\bf 27}, 1250173 (2012)] as a stable nucleus. A relatively higher cross-section value is noticed between 30Ar and 32Ar which infers that 32Ar is the most stable isotope among the considered chain. Moreover, we noticed that the profile of the differential cross-sections and scattering angle are highly influenced by the mass of the target nuclei and the magnitude of the incident energy of the projectile nucleus.

nucl-th↗

arXiv2022

Structure and reaction study of Z=120 isotopes using non-relativistic and relativistic mean-field formalism

An extensive study is carried out for the island of stability in the superheavy nuclei of Z=120 and N=164-220 within the effective field theory motivated relativistic mean-field (E-RMF) and the non-relativistic Skyrme-Hartree-Fock (SHF) approaches. The relativistic G3 and IOPB-I and non-relativistic SLy4 and SkMP parameter sets are used for the investigations. Surface properties such as symmetry energy, neutron pressure and the curvature coefficient of symmetry energy are discussed within the coherent density fluctuation model (CDFM) using the Skyrme and the Brückner energy density functionals. The volume and surface contributions of symmetry energy are evaluated using Danielewicz's liquid drop approximation within the CDFM. The total nuclear reaction and elastic differential cross-sections are also obtained for both SHF and E-RMF within the Glauber model. The peaks in the symmetry energy at N = 182 for SHF and N=184 for E-RMF are seen, which are absent in the Brückner functional. The shifting of peak in the symmetry energy with Brückner functional can be correlated to the Coester-band problem. The enhanced total reaction cross-section for relativistic density of $^{304}120$ suggests the extra stability of this nucleus. This further confirms the shell/sub-shell closure of N = 184 in E-RMF force. The differential cross-section shows its force independent nature and significant increase with the scattering angle.

nucl-th↗

arXiv2021

Systematic study of surface properties for Ne, Na, Mg, Al and Si isotopes in a coherent density fluctuation model using the relativistic mean field formalism

We have systematically studied the surface properties, such as symmetric energy, neutron pressure, and symmetry energy curvature coefficient for Ne, Na, Mg, Al, and Si nuclei from the proton to neutron drip-lines. The Coherent Density Fluctuation Model (CDFM) is used to estimate these quantities taking the relativistic mean-field densities as inputs. The Brückner energy density functional is taken for the nuclear matter binding energy and local density approximation is applied for its conversion to coordinate space. The symmetry energy again decomposed to the volume and surface components within the liquid drop model formalism to the volume and surface parts separately. Before calculating the surface properties of finite nuclei, the calculated bulk properties are compared with the experimental data, whenever available. The NL3* parameter set with the BCS pairing approach in an axially deformed frame-work is used to take care of the pairing correlation when needed. The deformed density is converted to its spherical equivalent with a two Gaussian fitting, which is used as an input for the calculation of weight function in the CDFM approximation. With the help of the symmetric energy for the recently isotopes $^{29}$F, $^{28}$Ne, $^{29,30}$Na and $^{31,35,36}$Mg are considered to be within the {\it island of inversion} emphasized {\bf [Phys. Lett. B 772, 529 (2017)]}. Although we get large symmetric energies corresponding to a few neutron numbers for this isotopic chain as expected, an irregular trend appears for all these considered nuclei. The possible reason behind this abnormal behavior of symmetry energy for these lighter mass nuclei is also included in the discussion, which gives a direction for future analysis.

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arXiv2021

Constraining the relativistic mean-field models from PREX-2 data: Effective forces revisited

Based on the current measurement of the neutron distribution radius ($R_n$) of $^{208}$Pb through the PREX-2 data, we re-visited the recently developed G3 and IOPB-I force parameter by fine-tuning some of the specific couplings within the relativistic mean-field model. The $ω-ρ-$mesons coupling $Λ_ω$ and the $ρ-$meson coupling $g_ρ$ are refitted to reproduce the experimental neutron radius of $^{208}$Pb without compromising the bulk properties of finite nuclei and infinite nuclear matter observables. The modified parameter sets are applied to calculate the gross properties of finite nuclei for a few double closed-shell nuclei and further used to obtain the various infinite nuclear matter observables at saturation. In addition to these, the force parameters are adopted to calculate the properties of high isospin asymmetry dense system such as neutron star matter and tested for the validation for the constraint from GW170817 binary neutron star merger events. The tuned forces are predicting relatively good results for finite and infinite nuclear matter systems and the current limitation on neutron radius from PREX-2. A systematic analysis using these two refitted parameter sets over the nuclear chat will be communicated shortly.

nucl-th↗

arXiv2021

Isotopic shift and search of magic number in the superheavy region

The ground state bulk properties such as binding energy, root-mean-square radius, pairing energy, nuclear density distributions, and single-particle energies are calculated for the isotopic chain of Ca, Sn, Pb, and Z = 120 nuclei. The relativistic mean-field with recently developed G3, IOPB-1, and Relativistic-Hartree-Bogoliubov with density-dependent DD-ME1 and DD-ME2 parameter sets are used in the present analysis. The respective shifts over the isotopic chain for the structural observables and surface property like symmetry energy are also estimated using a three-point method, which is crucial for the systematic analysis of the shell/sub-shell closure. The calculated results are compared with the available experimental data for various bulk properties, wherever available. A multiple isotopic shifts leads to the shell/sub-shell closure at N = (20 \& 28), (50 \& 82), and 126 for Ca, Sn, and Pb isotopes, respectively, are observed. The analysis also supports the neutron magic at N = 40 and 184 for highly neutron-rich $^{60}$Ca, and $^{304}$120, predicted to be the next double magic beyond $^{208}$Pb, respectively. Observing the occupancy number, we notice the higher neutron orbitals are mostly occupied before the lower one, which causes the kinks at neutron magic with an amalgam in the isotopic chain trend above nuclei. We also notice the correlation between the occupation probabilities and the magicity of a nucleus and vice-versa.

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