arXiv subjects

A. Sharma

Publications and source records attributed to A. Sharma.

At least 19 recordsLinked to original sources

arXiv2026

Gravity and Matter from Soldered Chiral Superconnections

We present a reformulation of four-dimensional chiral gravity in terms of a chiral gauge connection and a Clifford-valued coframe. The exterior algebra generated by $e^a \gamma_a$, together with the gauge curvature $F$, provides a natural and systematic construction of gauge-covariant differential forms. We show that suitable combinations of the chiral actions reproduce Einstein--Cartan--Holst gravity with a cosmological term. The original superconnection invariants yield only algebraic fermionic equations, so the fermionic one-forms do not propagate but instead generate a mass-like mixing between the two chiralities. Spinor propagation is supplied by a spinorial BF-type term, which under the matter ansatz reduces to the standard first-order Weyl kinetic action, including the torsion coupling. We also review the symmetry and variational properties of the matter ansatz, including its Lorentz equivariance, its relation to residual supersymmetry and twistor spinors, and the connection between the reduced and unrestricted field equations.

hep-th↗

arXiv2026

Treasure Search Optimization

We introduce Treasure Search Optimization (TSO), an interacting particle method for global optimization. Most swarm methods balance exploration and exploitation within a single population, and typically switch between the two by degenerating the noise, annealing a temperature, or tuning a parameter. TSO instead splits these tasks across two kinds of agents. A swarm of explorers stays in exploration mode and a single treasure hunter performs exploitation. The hunter drifts toward an objective-weighted average of the explorers and may teleport to it when the move lowers the objective. The swarm then re-centers around the hunter, creating a feedback loop between search and capture. We model the dynamics as coupled jump-diffusion stochastic differential equations (SDEs). The hunter's jumps are shared by all explorers and act as a common noise. The mean-field limit is therefore a conditional McKean-Vlasov jump-diffusion SDE, whose well-posedness we prove. We also characterize the steady state and prove, via Laplace approximation techniques, that the hunter settles near the global minimum with error of order $1/\alpha$, where $\alpha$ is the weight parameter. Linking the consensus drift to a smoothed free energy, we explain why the swarm ignores spurious local traps and demonstrate how to quantify uncertainty in inverse problems using post-processing Kalman steps after TSO iterations. Numerical experiments on ODE-constrained problems and a low dimensional Bayesian inverse problem demonstrate the effectiveness of the TSO method.

math.OC↗

arXiv2026

The non-LTE abundances of magnesium and yttrium and asteroseismic ages for the chemical clock calibration

Building on our previous study, which demonstrated the importance of accounting for departures from local thermodynamic equilibrium (LTE) in elemental-abundance determinations and of using asteroseismic ages, we investigate spatial variations in the empirical [Y/Mg]-age relation across the Galactic disc using a substantially larger stellar sample. We analysed high-resolution stellar spectra and determined Mg and Y abundances through spectral synthesis of multiple spectral features, rigorously accounting for non-LTE (NLTE) effects. We derived asteroseismic ages for stars exhibiting solar-type oscillations and used cross-checked isochrone-based methods for the remaining stars. We determined atmospheric parameters and Mg and Y abundances for 528 Galactic field stars, together with asteroseismic ages for 307 stars and isochronal ages for 221 stars. We also identified two new triple-lined and nine double-lined spectroscopic systems. Combining the present sample with that of our previous study yielded a total of 736 stars, which we used to examine the [Y/Mg]-age relation across the Galactic disc. The relation shows systematic spatial variations that likely reflect differences in star-formation and chemical-enrichment histories. In general, [Y/Mg] tends to increase with metallicity over the investigated age range. At supersolar metallicity, however, this trend may weaken, and the [Y/Mg]-age relations become flatter than those of solar-metallicity stars, which show lower [Y/Mg] values at young ages and higher values at old ages.

astro-ph.SR↗

arXiv2026

Switching Hamiltonian Monte Carlo for sampling from mixture distributions

We introduce a switching Hamiltonian Monte Carlo method for sampling from finite mixture Boltzmann-Gibbs distributions. We propose symmetric numerical integrators to approximate switching Hamiltonian dynamics interlaced with Poisson jumps, where the regime-switching chain is simulated using the uniformization technique or the stochastic simulation algorithm. We prove geometric ergodicity of the resulting Markov chain. We develop an approach based on the discrete Poisson equation associated with numerical schemes to estimate the error in computing ergodic averages. Using this approach we prove that the proposed numerical integrators have second-order bias. This approach is simple and can be generalized to other settings, for example, kinetic Langevin equations. Finally, we verify the convergence result via numerical experiment.

stat.CO↗

arXiv2026

Two-Dimensional Far-Field Correlations of X-ray Photon Pairs

We directly observe far-field correlations of x-ray photon pairs generated by spontaneous parametric down-conversion (SPDC). Using an energy-resolved, two-dimensional photon counting detector we record the full ring-shaped emission of both photons across a broad bandwidth and extract pair correlations directly from raw events without imposing angular constraints. The ring radii scale with photon energy, in quantitative agreement with transverse phase matching, providing a stringent momentum-space validation of x-ray SPDC. These observations open a route to leveraging quantum correlations in x-ray imaging and metrology, including correlation-enhanced magnification and reduced blurring.

quant-ph↗

arXiv2026

2025 EIC-France Workshop: Physics Highlights and Perspectives

This document presents a synthesis of the theory contributions and discussions from the 2nd EIC-France Workshop, held at IJCLab (Orsay) on 1-3 December 2025. The workshop brought together members of the French hadron-physics community to review recent theoretical developments relevant to the future Electron-Ion Collider (EIC) and to coordinate national efforts in preparation for its early physics program. The report first summarizes the collider's initial running conditions and luminosity performance, as outlined in the EIC Early Science Matrix. It then provides concise overviews of the theoretical presentations on inclusive, semi-inclusive, exclusive, heavy-flavor, and small-x physics. Based on these discussions, two measurements emerged as especially well suited for early EIC operation and strongly aligned with areas of established French expertise: inclusive diffraction and inclusive quarkonium production. These channels offer clean signatures, robust theoretical interpretability, and direct sensitivity to fundamental QCD phenomena such as gluon saturation, heavy-quark dynamics, and the small-x structure of hadrons and nuclei. In addition, the workshop identified longer-term physics opportunities that will benefit from the full capabilities of the EIC after its ramp-up phase. These include accessing the three-dimensional structure of the pion through the Sullivan process and a broader program of exclusive three-body final states, both of which represent high-impact avenues for exploring hadronic structure and non-perturbative QCD. Together, the elements summarized in this report provide a coherent overview of the strategic priorities and scientific ambitions shaping the French community's contribution to the EIC physics program.

hep-ph↗

arXiv2025

Aerodynamic Design Considerations for Biconic Supersonic Air Intakes Revisited

Traditional design principles for determining the optimal intake ramp or cone angles, for ensuring no flow spillage at the intake cowl under design conditions, and for the form of the terminal shock in the intake duct are revisited. We show that it is preferable to select the ramp or cone angles to be somewhat smaller than that suggested by the Oswatitsch criterion. An offset cowl lip that slightly violates the shock-on-lip condition is found to be beneficial; in fact, an offset cowl can be arranged for conical intakes with no flow spillage at the cowl lip at all. Improvements to the total pressure recovery are seen when the terminal normal shock is replaced by a strong form of the oblique shock for two-dimensional ramp-type intakes, and with a Lambda shock in case of conical intakes. The necessary design modifications are simple and virtually cost-free. These results rewrite the ground rules for the aerodynamic design of supersonic intakes.

physics.flu-dyn↗

arXiv2025

Chemical composition of planetary hosts: II. Abundances of neutron-capture elements

We present a study of neutron-capture element abundances (Sr, Y, Zr, Ba, La, Ce, Nd, Pr, and Eu) in a large and homogeneous sample of 160 F-, G-, and K-type planet-host stars located in the northern hemisphere, including 32 stars in multi-planetary systems. The sample hosts a total of 175 high-mass planets and 47 Neptunian and super-Earth planets. High-resolution spectra were obtained with the 1.65-metre telescope at the Mol\.etai Astronomical Observatory using a fibre-fed spectrograph covering 4000-8500 \r{A}. Elemental abundances were determined by differential line-by-line spectrum synthesis with the TURBOSPECTRUM code and MARCS model atmospheres. The analysis of $[\mathrm{El}/\mathrm{Fe}]$ ratios shows that most elements in PHSs follow the Galactic chemical evolution, but $[\mathrm{Zr}/\mathrm{Fe}]$, $[\mathrm{La}/\mathrm{Fe}]$, and $[\mathrm{Ce}/\mathrm{Fe}]$ are overabundant in PHSs relative to reference stars at a given $[\mathrm{Fe}/\mathrm{H}]$. Correlations between $[\mathrm{El}/\mathrm{Fe}]$ and planet mass are generally positive, except for Sr, Y, and Ba, which show no significant trends. The distribution of $\Delta[\mathrm{El}/\mathrm{H}]$ versus condensation temperature ($T_{\mathrm{cond}}$) slopes is positively skewed for PHSs, indicating enrichment in refractory elements compared to analogues. While no strong correlations are found between $\Delta[\mathrm{El}/\mathrm{H}]$-$T_{\mathrm{cond}}$ slopes and stellar or planetary parameters, older dwarf stars with multiple planets tend to have smaller or negative slopes, whereas younger dwarf stars exhibit larger positive slopes. Our results also confirm that multi-planetary systems are more frequent around metal-rich stars.

astro-ph.SR↗

arXiv2025

Pixel column issue in the ATLAS Inner Tracker modules

Pixel modules are currently being built for the ATLAS ITk Pixel detector upgrade. During the preproduction phase, recurring chip malfunctioning was observed during electrical testing. It was possible to bypass this issue by disabling some pixel core columns in the ITkPix readout chip. Therefore the issue is called "core column issue" which is a direct disqualifier for a pixel module. A concerning number of cases has been observed in pixel modules with ITkPix v1.1 as well as v2 chips which significantly impacts the module yield. However, the behaviour is erratic and there is not any evidence hinting at the origin of this issue. These proceedings outline the investigations of the issue, highlighting the electrical behaviour during testing, present findings from the data collected via our production database and through visual inspection, and point towards possible causes of the issue.

physics.ins-det↗

arXiv2025

Minimal material, maximum coverage: Silicon Tracking System for high-occupancy conditions

Silicon strip sensors have long been a reliable technology for particle detection. Here, we push the limits of silicon tracking detectors by targeting an unprecedentedly low material budget of 2%-7% $X_0$ in an 8-layer 4 m$^2$ detector designed for high-occupancy environments ($\leq$ 10 MHz/cm$^2$). To achieve this, we employ Double-Sided Double Metal (DSDM) silicon microstrip sensors, coupled with readout electronics capable of precise timing and energy measurements. These 320 $\mu$m thick sensors, featuring $2\times 1024$ channels with a 58 $\mu$m pitch, are connected via ultra-lightweight aluminium-polyimide microcables for signal transmission and integrated with a custom SMX readout ASIC, operating in free-streaming mode. This system enables the simultaneous measurement of time ($\Delta t \simeq 5$~ns) and charge deposition (0.1-100 fC), significantly enhancing the detector's capacity for high-precision track reconstruction in high-occupancy and harsh radiation field environments. The primary application of this technology is the Silicon Tracking System (STS) for the CBM experiment, with additional potential in projects like the J-PARC E16 experiment and future uses in medical physics, such as advanced imaging telescopes. In this contribution, we present the current status of CBM STS construction, with almost one-third of the modules produced and tested. We also discuss immediate applications and explore promising prospects in both scientific and medical fields.

physics.ins-det↗

arXiv2025

Tradeoffs in Biconic Intake Aerodynamic Design Optimization with Sub-optimal Oswatitsch Solutions

The notion of sub-optimal Oswatitsch solutions is introduced in order to systematically conduct a tradeoff between total pressure recovery (TPR) and intake drag coefficient (CDi) for supersonic intakes. It is shown that the Oswatitsch-optimal TPR for a biconic intake may be enhanced by adding a conical flare which modifies the terminal normal shock into a novel Lambda shock structure. The optimization problem is formulated along the lines of Axiomatic Design Theory with the conical angle pair and the cowl fineness ratio as the two design parameters. Reynolds-averaged Navier-Stokes (RANS) simulations are performed to iteratively arrive at the optimal solutions, with and without an intake length constraint, for a fixed value of the intake mass flow rate. The results are used to generate the Pareto front in the space of the objective functions, which yields the set of solutions between which TPR and Cdi may be traded off for one another. Additionally, an off-Oswatitsch solution, where only the second cone angle is altered from its optimal Oswatitsch value, is obtained and is compared with the sub-optimal Oswatitsch solutions that form the Pareto front.

physics.flu-dyn↗

arXiv2024

Well-posedness and approximation of reflected McKean-Vlasov SDEs with applications

In this paper, we establish well-posedness of reflected McKean-Vlasov SDEs and their particle approximations in smooth non-convex domains. We prove convergence of the interacting particle system to the corresponding mean-field limit with the optimal rate of convergence. We motivate this study with applications to sampling and optimization in constrained domains by considering reflected mean-field Langevin SDEs and two reflected consensus-based optimization (CBO) models, respectively. We utilize reflection coupling to study long-time behaviour of reflected mean-field SDEs and also investigate convergence of the reflected CBO models to the global minimum of a constrained optimization problem. We numerically test reflected CBO models on benchmark constrained optimization problems and an inverse problem.

math.PR↗

arXiv2024

Computationally-guided discovery and synthesis of the amorphous nitride Y2WN4

Amorphous materials offer unique functional characteristics, which are often not observed in their crystalline counterparts. This makes them invaluable for many technological applications, such as diffusion barriers in semiconductor devices. However, the computationally guided search for new functional amorphous materials with attractive properties represents a major challenge. In this work, we combine theory and experiment to discover and synthesize the amorphous ternary nitride Y2WN4. We show how computational random structure sampling offers a route to robustly identify chemistries which are hard to crystallize. Experiments prove that the predicted nitride is easily synthesized in amorphous phase with no detectable precipitates. The material exhibits remarkable stability against crystallization at high temperature and as well as excellent oxidation resistance and stability against Cu diffusion. Moreover, Y2WN4 exhibits a sharp onset of optical absorption and an indirect band gap of 2.24 eV. These properties make this material promising for the integration in electronic devices as a high-performance diffusion barrier with adjustable band edges.

cond-mat.mtrl-sci↗

arXiv2024

Combining integral equation closures with force density functional theory for the study of inhomogeneous fluids

Classical density functional theory (DFT) is a powerful framework to study inhomogeneous fluids. Its standard form is based on the knowledge of a generating free energy functional. If this is known exactly, then the results obtained by using standard DFT or its alternative, recently developed version, force-DFT, are the same. If the free energy functional is known only approximately then these two routes produce different outcomes. However, as we show in this work, force-DFT has the advantage that it is also implementable without knowledge of the free energy functional, by using instead liquid-state integral equation closures. This broadens the range of systems that can be explored, since free energy functionals are generally difficult to approximate. In this paper we investigate the utility of using inhomogeneous integral equation closures within force-DFT thus demonstrating the versatility and accuracy of this approach.

cond-mat.soft↗

arXiv2024

Chemical composition of planetary hosts: C, N, and $\alpha$-element abundances

Accurate atmospheric parameters and chemical composition of planet-hosting stars are crucial for characterising exoplanets and understanding their formation and evolution. Our objective is to uniformly determine the atmospheric parameters and chemical abundances of carbon, nitrogen, oxygen, and the $\alpha$-elements, magnesium and silicon, along with C/O, N/O and Mg/Si abundance ratios in planet-hosts. We aim to investigate the potential links between stellar chemistry and the presence of planets using high-resolution spectra of 149 F, G, and K dwarf and giant stars hosting planets or planetary systems. The spectra were obtained with the Vilnius University Echelle Spectrograph on the 1.65 m Mol\.{e}tai Observatory telescope. Stellar parameters were determined through standard analysis using equivalent widths and one-dimensional, plane-parallel model atmospheres calculated under the assumption of local thermodynamical equilibrium. The differential synthetic spectrum method was used to uniformly determine carbon C(C2), nitrogen N(CN), oxygen [O I], magnesium Mg I, and silicon Si I elemental abundances as well as the C/O, N/O, and Mg/Si ratios. We found that [C/Fe], [O/Fe], and [Mg/Fe] are lower in metal-rich dwarf hosts; whereas [N/Fe] is close to the Solar ratio. Giants show smaller scatter in [C/Fe] and [O/Fe] and lower than the Solar average [C/Fe] and C/O ratios. The (C+N+O) abundances increase with [Fe/H] in giant stars, with a minimal scatter. We also noted an overabundance of Mg and Si in planet hosting stars, particularly at lower metallicities, and a lower Mg/Si ratio in stars with planets. In giants hosting high-mass planets, nitrogen shows a moderate positive relationship with planet mass. C/O and N/O ratios show moderate negative and positive slopes in giant stars, respectively. The Mg/Si ratio shows a negative correlation with planet mass across the entire stellar sample.

astro-ph.SR↗

arXiv2024

Raman signal enhancement via a microring resonator

Micro-ring resonators (MRRs) "trap" incoming light, and therefore, have been shown to achieve extremely high local intensities of light. Thus, they can be used to facilitate highly non-linear optical signals. By embedding materials that host non-linear optical processes inside the MRR, we expect to observe an enhancement in the strength of the non-linear optical signal. This concept is demonstrated here by extracting the Raman signature of graphene that is placed inside a MRR. A highly doped silica MRR which features an optical bus waveguide coupled to a loop (ring) tuned to near-infrared wavelengths is used. Raman signal with an excitation wavelength of 522 nm via third harmonic generation inside the MRR is observed. Higher order Raman signal of the embedded graphene at the 1597.6 nm excitation wavelength is also observed. This work demonstrates the feasibility of the MRR as a non-linear signal enhancer using novel MRR device setups.

cond-mat.mes-hall↗

arXiv2024

Turbojet Module Sizing for Integration with Turbine-Based Combined Cycle Engine

A turbine-based combined cycle (TBCC) vehicle is studied that relies on a scramjet engine for high-speed flight but requires a turbojet module to accelerate it to a high supersonic handover Mach number. The challenge is to scale a given turbojet engine (TJE) core (compressor, burner, turbine) to a particular value of the air mass flow rate such that the desired thrust at the handover point is achieved. To this end, a model for the engine core is integrated with a supersonic intake model that is designed to supply the required mass flow rate, and a nozzle model that is expected to deliver the desired thrust. Both the TJE intake and nozzle are constrained by the design choices made for the DMSJ module, and the TJE core is itself constrained by the volume available from the TBCC vehicle sizing for hypersonic flight. The TJE module is sized by scaling the engine core with matching intake and nozzle designs in an iterative manner until the process converges to a solution with acceptable thrust satisfying all the system constraints. The task turns out to be non-trivial due to the scarcity of steady operating points for the engine core at high speeds, due to possible mismatch between the mass flow rate demanded by the compressor and that delivered by the supersonic intake, and due to the difficulty in adapting a DMSJ-style single-expansion ramp nozzle (SERN) to adequately expand the turbojet exhaust flow.

physics.flu-dyn↗

arXiv2024

Numerical integrators for confined Langevin dynamics

We derive and analyze numerical methods for underdamped (kinetic) Langevin dynamics in a domain with elastic reflection at the boundary. First-order approximations are based on an Euler-type scheme incorporating collision-handling at the boundary. To achieve second order, composition schemes are derived based on decomposition of the generator into collisional drift, impulse, and stochastic momentum evolution. In a deterministic setting, this approach would typically lead to first-order approximation, even in symmetric compositions, but we find that the stochastic method can provide second-order weak approximation with a single gradient evaluation, both at finite times and in the ergodic limit. We provide analysis of this observation, as well as numerical demonstration, and we compare and contrast the performance of different variants of the integration method using model problems.

math.NA↗