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A. Bhagwat

Publications and source records attributed to A. Bhagwat.

17 recordsLinked to original sources
arXiv2026

The gradual decline of Ly$α$ visibility in the CANDELS fields: evidence for the combined effects of galaxy evolution and reionization

We investigate the evolution of Ly$α$ visibility and the physical properties of Ly$α$ emitters (LAEs) across the five CANDELS fields using publicly available JWST/NIRSpec PRISM spectroscopy. Our catalog comprises 3446 spectroscopically confirmed sources at 4 $\leq $ z < 14.2, including 3361 star-forming galaxies (SFGs), of which 539 are robust (S/N > 3) LAEs. We measure the fraction of LAEs with EW$_0$ > 25A (X$_{\mathrm{Lyα}}$) and trace its redshift evolution in two UV luminosity bins, namely -20.25 < M$_{\mathrm{UV}}$ < -18.75 and -21.75 < M$_{\mathrm{UV}}$ < -20.25. Within the fainter-UV range, X$_{\mathrm{Lyα}}$ increases from z = 5 to z = 6 at 3$σ$ significance and subsequently declines toward higher redshifts with a significant monotonic trend at z > 6. We also investigate the physical properties of both LAEs and the full SFG population. We find that the stellar mass, UV slope $β$, stellar reddening, SFR, metallicity, sSFR, and burstiness of LAEs remain approximately stable with redshift. The only exception is the mass-weighted age which decreases with increased redshift. Conversely, the properties of the full SFG population evolve significantly, progressively approaching the region of galaxy-property space occupied by LAEs as redshift increases. This suggests that galaxy evolution may enhance the intrinsic production and escape of Ly$α$ photons toward earlier epochs. We argue that this effect should be accounted when inferring the evolution of the neutral hydrogen content of the IGM from the observed visibility of Ly$α$ emission. To this end, we employ a physically motivated framework based on the Attenuation-Free Model, jointly accounting for galaxy evolution and IGM attenuation. Our observations favor reionization histories that proceed gradually over scenarios characterized by a rapid increase in the cosmic neutral hydrogen fraction.

astro-ph.GA↗
arXiv2026

The Collective Voice of Ly$α$ Emitters: Insights from JWST Stacked Spectroscopy

We present a spatially resolved stacked analysis of 287 LAEs at $z>4$ observed with JWST/NIRSpec prism spectroscopy. By constructing a two-dimensional stack from public surveys (CAPERS, CEERS, JADES, and RUBIES), we probe the average internal structure of typical LAEs on sub-kiloparsec scales. We find a clear radial decoupling between resonant and non-resonant emission: while EW(H$β$) and other optical lines decline with radius, EW(Ly$α$) increases toward the outskirts, and the Ly$α$ escape fraction rises from $\sim16\%$ in the center to $\gtrsim24\%$ at larger radii. This behavior suggests that resonant scattering redistributes Ly$α$ photons into lower-density outer regions, where escape becomes more efficient. Optical diagnostics and $T_e$ measurements reveal low metallicities ($12+\log(\rm O/H)\simeq7.7\pm0.2$), high ionization parameters, negligible dust attenuation, and systematically elevated N/O ratios ($\log({\rm N/O})\sim-0.4$). The latter place typical LAEs among the growing population of nitrogen-enhanced high-redshift galaxies, pointing to rapid and possibly feedback-driven chemical enrichment. The inferred ionizing photon production efficiency, $\log(ξ_{\rm ion}/{\rm Hz\,erg^{-1}})\simeq25.1-25.2$, together with the high Ly$α$ escape fractions, suggests that these systems are efficient, though not extreme, contributors to the ionizing photon budget. Comparison with SPICE radiation-hydrodynamic simulations shows that bursty supernova feedback models naturally reproduce the observed radial trends in Ly$α$ escape, UV slope, and emission-line equivalent widths, linking the spatial redistribution of Ly$α$ to stochastic star formation and feedback-driven gas flows. Our results demonstrate that Ly$α$ emission, chemical enrichment, and feedback are tightly connected in typical $z>4$ LAEs. (Shortened version for arXiv)

astro-ph.GA↗
arXiv2026

Ly$α$ visibility from z = 4.5 to 11 in the UDS field: Evidence for a high neutral hydrogen fraction and small ionized bubbles at z $\sim$ 7

The resonant scattering nature of Ly$α$ photons interacting with neutral hydrogen makes Ly$α$ emitters (LAEs) robust tracers of the intergalactic neutral hydrogen fraction, and thus sensitive probes of cosmic reionization. We present an extensive study of the Ly$α$ evolution from galaxies at 4.5 $\leq$ z $\leq$ 11 in the UDS field, observed as part of the CAPERS survey, and complemented with spectra from the DAWN JWST Archive. The combined sample includes 651 spectroscopically confirmed Ly$α$-break galaxies, among which we find 73 S/N>3 LAEs in JWST-NIRSpec PRISM spectra. We trace the redshift evolution of the LAE fraction with EW$_0$ >25 A (X$_{\mathrm{Lyα}}$) between z = 5 and z = 9, extending such an analysis to the UDS field for the first time. At z = 5 and 6, the UDS results agree with the average JWST X$_{\mathrm{Lyα}}$ values from multiple fields. However, JWST measurements are consistently lower than ground-based results. To investigate this, we compare JWST observations to a population of star-forming galaxies at z$\sim$6 observed with VLT-FORS2. We find that a Ly$α$ slit-loss of 35 $\pm$ 10% in JWST spectra accounts for the offset, as the resonant Ly$α$ emission is more spatially extended than the stellar continuum. From z = 6 to 7, the UDS field shows a significant drop in Ly$α$ visibility, from which we infer a neutral hydrogen fraction of X$_{\mathrm{HI}}$ = 0.7--0.9. Finally, we identify two robust ionized bubbles at z = 7.29 and 7.77, with radii of $R_{\mathrm{ion}}$ = 0.6 and 0.5 physical Mpc and photometric overdensities of N/$\langle$N$\rangle$ = 3 and 4, based on candidate counts down to the photometric completeness limit. Compared to the large ionized region at z$\sim$7 in the EGS field, these results indicate significant field-to-field variation, supporting a patchy, inhomogeneous reionization process.

astro-ph.GA↗
arXiv2025

PT-Symmetric $SU(2)$-like Random Matrix Ensembles: Invariant Distributions and Spectral Fluctuations

We consider an ensemble of $2\times 2$ normal matrices with complex entries representing operators in the quantum mechanics of 2 - level parity-time reversal (PT) symmetric systems. The randomness of the ensemble is endowed by obtaining probability distributions based on symmetry and statistical independence. The probability densities turn out to be power law with exponents that depend on the boundedness of the domain. For small spacings, $σ$, the probability density varies as $σ^ν$, $ν\geq 2$. The degree of level repulsion is a parameter of great interest as it makes a connection to quantum chaos; the lower bound of $ν$ for our ensemble coincides with the Gaussian Unitary Ensemble. We believe that the systematic development presented here paves the way for further generalizations in the field of random matrix theory for PT-symmetric quantum systems.

math-ph↗
arXiv2024

Tunneling half-lives in macroscopic-microscopic picture

Tunneling half lives are obtained in a minimalistic deformation picture of nuclear decays. As widely documented in other deformation models, one finds that the effective mass of the nucleus changes with the deformation parameter. However, contrary to the approach used in literature, a position-dependant mass potentially makes using WKB tunneling probabilities unreliable for estimating nuclear lifetimes. We instead use a new approach, a combination of the Transmission Matrix and WKB methods, to estimate tunneling probabilities. Because of the simplistic nature of the model, the calculated lifetimes are not accurate, however, the relative trends in the lifetimes of isotopes of individual nuclei are found to be consistent. Using this, we develop an empirical scaling to obtain the actual half-lives, and find the primary scaling parameter to have remarkably consistent values for all nuclei considered. The new tunneling method proposed here, which produces very different probabilities as compared to the usual WKB approach, is another key result of this work, and can be utilized for arbitrary potentials and mass variations.

nucl-th↗
arXiv2024

Nuclear stability and the Fold Catastrophe

A geometrical analysis of the stability of nuclei against deformations is presented. In particular, we use Catastrophe Theory to illustrate discontinuous changes in the behavior of nuclei with respect to deformations as one moves in the N - Z space. We construct a minimalistic deformation model using the microscopic-macroscopic approach. A third-order phase transition is found in the liquid-drop model, which translates to a complete loss of stability (using the Fold catastrophe) when shell effects are included. The analysis is found to explain the instability of known fissile nuclei and also justify known decay chains of heavy nuclei.

nucl-th↗
arXiv2023

Universality in Ground State Masses of Nuclei

The beautiful and profound result that the first eigenvalue of Schroedinger operator can be interpreted as a large deviation of certain kind of Brownian motion leads to possible existence of universality in the distribution of ground state energies of quantal systems. Existence of such universality is explored in the distribution of the ground state energies of nuclei with Z $\ge$ 8 and N $\ge$ 8. Specifically, it has been demonstrated that the nuclear masses follow extreme-value statistics, implying that the nuclear ground state energies indeed can be treated as extreme values in the sense of the large deviation theory of Donsker and Varadhan.

nucl-th↗
arXiv2022

A Study on the Scattering of Matter Waves through Slits

Scattering of matter waves through slits has been explored using the Feynman Path Integral formalism. We explicitly plot the near-zero probability densities to analyse the behaviour near the slit. Upon doing so, intriguing patterns emerge, most notably the braid-like structure in the case of double slits, whose complexity increases as one increases the number of slits. Furthermore, the plot shows the existence of a transition region, where the distribution of near-zero probability points changes from the braided to the fringe-like structure, which has been analysed by explicitly expressing the wavefunction as a hypergeometric function. These patterns are analysed while considering the continuity equation and its consequences for the regions with zero probability density. As a result, we find quasi-traps in the region whose size can be controlled and made much smaller than the wavelength of matter waves.

quant-ph↗
arXiv2020

Microscopic-Macroscopic Approach for Ground-State Energies Based on the Gogny Force with the Wigner-Kirkwood Averaging Scheme

In the previous paper I \cite{bhagwat20} we have shown that self-consistent Extended Thomas-Fermi (ETF) potentials and densities associated with a given finite-range interaction can be parametrized by generalized Fermi distributions. As a next step, a comprehensive calculation of ground-state properties of a large number of spherical and deformed even-even nuclei is carried out in the present work using the Gogny D1S force within the ETF scheme. The parametrized ETF potentials and densities of paper I are used to calculate the smooth part of the energy and the shell corrections within the Wigner-Kirkwood semiclassical averaging scheme. It is shown that the shell corrections thus obtained, along with a simple liquid drop prescription, yield a good description of ground-state masses and potential energy surfaces for nuclei spanning the entire periodic table.

nucl-th↗
arXiv2018

Taylor approximation to treat nonlocality in scattering processes

Study of scattering process in the nonlocal interaction framework leads to an integro-differential equation. The purpose of the present work is to develop an efficient approach to solve this integro-differential equation with high degree of precision. The method developed here employs Taylor approximation for the radial wave function which converts the integro-differential equation in to a readily solvable second-order homogeneous differential equation. This scheme is found to be computationally efficient by a factor of 10 when compared to the iterative scheme developed in J.~Phys.~G~Nucl.~Part.~Phys.~{\bf 45},~015106~(2018). The calculated observables for neutron scattering off $^{24}$Mg, $^{40}$Ca, $^{100}$Mo and $^{208}$Pb with energies up to 10 MeV are found to be within at most 8$\%$ of those obtained with the iterative scheme. Further, we propose an improvement over the Taylor scheme that brings the observables so close to the results obtained by iterative scheme that they are visually indistinguishable. This is achieved without any appreciable change in the run time.

nucl-th↗
arXiv2018

Microscopic description of the ground state properties of recently reported new isotopes

Microscopic investigations for the observed properties of the recently reported five unstable new isotopes are carried out. The ground state properties are calculated in the relativistic mean field (RMF) framework and the results reproduce the experiment well as expected. The α - decay lifetimes are calculated in the double folding model using WKB approximation which requires the relevant Q values of α - decay and the α - daughter potential. The latter is obtained by folding the effective M3Y nucleon nucleon potential with the RMF nucleon density distributions for the daughter nucleus and that of the α particle which is assumed to be of Gaussian shape. the corresponding decay half - lives obtained by using available phenomenological expression are also presented, discussed and compared. It is observed that the Q values calculated in the RMF framework , though reasonably agree with the experiment, are not accurate enough for the reliable WKB calculation of decay half- lives. We therefore, advocate that the use of accurate (e.g. experimental) Q values is crucial for the reliable description of the experimental α - decay half-lives.

nucl-th↗
arXiv2018

A new treatment of nonlocality in scattering process

Nonlocality in the scattering potential leads to an integro-differential equation.In this equation nonlocality enters through an integral over the nonlocal potential kernel. The resulting Schroedinger equation is usually handled by approximating r,r'-dependence of the nonlocal kernel. The present work proposes a novel method to solve the integro-differential equation. The method, using the mean value theorem of integral calculus, converts the nonhomogeneous term to a homogeneous term. The effective local potential in this equation turns out to be energy independent, but has relative angular momentum dependence. This method has high accuracy and is valid for any form of nonlocality. As illustrative examples, the total and differential cross sections for neutron scattering off 12C, 56Fe and 100Mo nuclei are calculated with this method in the low energy region (up to 10 MeV) and are found to be in good accord with the experiments.

nucl-th↗
arXiv2012

Microscopic-Macroscopic Approach for Binding Energies with the Wigner-Kirkwood Method - II

The binding energies of deformed even-even nuclei have been analysed within the framework of a recently proposed microscopic-macroscopic model. We have used the semiclassical Wigner - Kirkwood $\hbar$ expansion up to fourth - order, instead of the usual Strutinsky averaging scheme, to compute the shells corrections in a deformed Woods - Saxon potential including the spin-orbit contribution. For a large set of 561 even-even nuclei with $Z\ge 8$ and $N\ge 8$, we find an {\it rms} deviation from the experiment of 610 keV in binding energies, comparable to the one found for the same set of nuclei using the FRDM of Möller and Nix (656 keV). As applications of our model, we explore its predictive power near the proton and neutron drip lines as well as in the superheavy mass region. Next, we systematically explore the fourth - order Wigner - Kirkwood corrections to the smooth part of the energy. It is found that the ratio of the fourth - order to the second - order corrections behaves in a very regular manner as a function of the asymmetry parameter $I=(N-Z)/A$. This allows to absorb the fourth - order corrections into the second - order contributions to the binding energy, which enables to simplify and speed up the calculation of deformed nuclei.

nucl-th↗
arXiv2009

Microscopic-Macroscopic Approach for Binding Energies with Wigner-Kirkwood Method

The semi-classical Wigner-Kirkwood $\hbar$ expansion method is used to calculate shell corrections for spherical and deformed nuclei. The expansion is carried out up to fourth order in $\hbar$. A systematic study of Wigner-Kirkwood averaged energies is presented as a function of the deformation degrees of freedom. The shell corrections, along with the pairing energies obtained by using the Lipkin-Nogami scheme, are used in the microscopic-macroscopic approach to calculate binding energies. The macroscopic part is obtained from a liquid drop formula with six adjustable parameters. Considering a set of 367 spherical nuclei, the liquid drop parameters are adjusted to reproduce the experimental binding energies, which yields a {\it rms} deviation of 630 keV. It is shown that the proposed approach is indeed promising for the prediction of nuclear masses.

nucl-th↗
arXiv2007

Critical Survey of Isoscalar and Isovector Contributions to the Spin Orbit Potential in Relativistic Mean Field Theory

The spin-orbit (SO) interaction, emerging naturally from the Relativistic Mean Field (RMF) theory is examined critically in the light of the recently measured excitation energy differences between the terminating states built on two different configurations for nuclei belonging to the lower pf shell. The calculations are carried out using the cranked RMF framework. To further probe the iso-vector dependence of the spin-orbit potential, the energy spacing between the g_{7/2} and h_{11/2} states in the Sb-chain is compared to experiment. It is found that the calculation at the quantitative level deviates strongly from the experiment. In particular the balance of the iso-scalar and iso-vector strengths of the effective one body SO potential indicates that additional terms like tensor couplings may be needed to account for the experimental data.

nucl-th↗
arXiv2005

Microscopic Description of Super Heavy Nuclei

The results of extensive microscopic Relativistic Mean Field (RMF) calculations for the nuclei appearing in the alpha - decay chains of recently discovered superheavy elements with Z = 109 to 118 are presented and discussed. The calculated ground state properties like total binding energies, Q values, deformations, radii and densities closely agree with the corresponding experimental data, where available. The double folding (t-rho-rho) approximation is used to calculate the interaction potential between the daughter and the alpha, using RMF densities along with the density dependent nucleon - nucleon interaction (M3Y). This in turn, is employed within the WKB approximation to estimate the half lives without any additional parameter for alpha - decay. The half lives are highly sensitive to the Q values used and qualitatively agree with the corresponding experimental values. The use of experimental Q values in the WKB approximation improves the agreement with the experiment, indicating that the resulting interaction potential is reliable and can be used with confidence as the real part of the optical potential in other scattering and reaction processes.

nucl-th↗