arXiv subjects

S. Ray

Publications and source records attributed to S. Ray.

At least 19 recordsLinked to original sources

arXiv2026

Magnetic ordering in VI3: a van der Waals material combining vastly different magnetic anisotropies

Among magnetic van der Waals materials, the vanadium trihalide family exhibits unique features. In particular, VI3 contains V atoms of two different types, as two energetically close electronic occupations can coexist in real samples. These types show strikingly different magnetic anisotropy, predicted to differ by more than an order of magnitude. The combination forms a distinctive magnetic system. VI3 also displays an unusual thickness dependence: the monolayer Curie temperature (TC) is higher than that of the bulk, contrary to the expectation that interlayer coupling reinforces magnetic order. Using atomistic spin-dynamics simulations informed by first-principles calculations, we investigate the critical temperature behavior from the combined perspective of single-ion anisotropy and exchange interactions. The strong anisotropy contrast significantly affects thermal stability: increasing the fraction of high-anisotropy sites raises the energy cost of transverse spin fluctuations and increases the ordering temperature. Furthermore, V-atom inhomogeneity makes the interlayer super-superexchange network spatially nonuniform, creating competing exchange pathways. This weakens coherent interlayer order while preserving robust intralayer ferromagnetic correlations, thus modifying the bulk-monolayer TC relation. Our model reproduces experimental TC values when the ratio of the two V types is close to 1:1, in agreement with two experimental methods. This supports the coexistence of two V configurations in VI3. The monolayer TC is reproduced with a slightly modified ratio, possibly linked to polaron concentration. The sensitivity of TC to this ratio suggests that the ordering temperature of VI3 can in principle be tuned over a broad range by controlling the relative occupation of the two vanadium configurations.

cond-mat.mtrl-sci↗

arXiv2026

Scale-valued sets: a minimal framework for generalized set models

Many generalized set models have the same basic form: they assign a value to each object, and the main difference lies in the kind of values that are allowed. This paper studies that common form through scale-valued sets (SV-sets), defined as maps $U\times E\to\Sigma$, where $U$ is a universe, $E$ is a parameter set, and $\Sigma$ is a bounded De Morgan lattice. With a suitable choice of scale, SV-sets include ordinary sets, fuzzy sets, soft sets, bounded multisets, intuitionistic fuzzy sets, $L$-fuzzy sets, and Type-2 fuzzy sets. We study the basic structure of SV-sets. The relation between SV-sets and lattice-valued interval soft sets is also discussed. For complete chains, the SV setting gives a natural topological construction, and for groups, it gives an algebraic structure through SV-subgroups. The applications show how graded suitability and supporting evidence can be kept together in a single model, whereas one-coordinate reductions lose information.

math.GM↗

arXiv2026

Soft Uniform Spaces and Soft Uniform Continuity: Induced Topologies, Separation, and Compactness-Type Results

Soft uniform structures provide a way to describe uniform closeness in a parameterized setting. Over a fixed parameter set, entourages are treated as soft relations, and a soft uniformity is defined by axioms parallel to the classical entourage axioms. Each soft uniformity induces two related topologies: a sectionwise soft topology $\tau_{\sU}$ on $F$, and an ordinary soft-element topology $\TU$ on $\SE(F)$. Both constructions are described. The space $(\SE(F),\TU)$ is Hausdorff, equivalently $T_1$, exactly when the soft uniformity is separated, and it is regular for every soft uniformity. Soft uniformly continuous mappings are then studied, and a Heine--Cantor type theorem is proved when the soft-element topology of the domain is compact. Finally, total boundedness and completeness are formulated for the canonical soft-element uniform space $(\SE(F),\sU_{\SE})$, and compactness of $(\SE(F),\TU)$ is shown to imply both properties. Examples relate the theory to uniformities generated by classical structures and illustrate the role of the parameter set.

math.GN↗

arXiv2026

Soft Bitopological Groups via Soft Elements

Let $F$ be a soft group over a parameter set $A$. We equip the selector group $\mathrm{SE}(F)=\prod_{t\in A}F(t)$ with the topology generated by componentwise open boxes. This construction replaces a sectionwise rule that does not define a topology on arbitrary selector subsets. It depends only on the component topologies and may therefore lose correlations between parameters. A soft bitopological group is then a soft group with two selector topologies, each making $\mathrm{SE}(F)$ a topological group. We also study a soft paratopological group together with its inverse topology. In this conjugate pair, inversion interchanges the two selector topologies, and equality of the two is equivalent to continuity of inversion. We prove componentwise separation criteria, finite-parameter compactness and $\omega$-boundedness results, and infinite-parameter counterexamples caused by the box topology. We also characterize when a soft union creates mixed selectors outside the two original selector sets.

math.GN↗

arXiv2026

A Spectral Fractional Hirota Bilinear Operator: Analysis and Application to a Time-Fractional KdV Equation

We develop a fractional version of Hirota's bilinear calculus that is built directly from the spectral (Fourier-multiplier) fractional derivative on $\mathbb{R}$. For $0<\alpha\le 1$ we define \[ D_{\xi}^{\alpha}f\cdot g := (D_{\xi}^{\alpha}f)\,g - f\,(D_{\xi}^{\alpha}g), \] equivalently through the two-variable extension $D_{\xi_1}^{\alpha}-D_{\xi_2}^{\alpha}$. In Fourier variables this is a bilinear multiplier with symbol $(ik_1)^{\alpha}-(ik_2)^{\alpha}$. For $0<\alpha<1$ we prove a Marchaud-type singular integral representation, and we use it to establish basic algebraic identities (bilinearity, skew-symmetry and $D_{\xi}^{\alpha}f\cdot f=0$), a Sobolev estimate $H^{s}\times H^{s}\to H^{s-\alpha}$ for $s>\tfrac12$, and convergence to the classical Hirota derivative as $\alpha\to 1^-$. As an application we derive a Hirota bilinear form for a spectral time-fractional KdV equation and construct explicit one- and two-soliton $\tau$-functions. The fractional order changes the dispersion relation to $\omega^{\alpha}=-k^{3}$, while the two-soliton interaction coefficient agrees with the classical KdV value.

math.AP↗

arXiv2026

JWST/MIRI coronagraphic search for planets in systems with gapped exoKuiper belts and proper motion anomalies

Over the past decade, ALMA has uncovered a range of substructures within exoKuiper belts, pointing to a population of undetected planets. With JWST's sensitivity, we now have the opportunity to identify these planets thought to be responsible for the observed substructures in debris discs. We present Cycle 1 JWST/MIRI 11.4 {\mu}m coronagraphic observations of three exoKuiper belts that exhibit gaps in their radial structures: HD 92945, HD 107146, and HD 206893, to determine whether planets are responsible for carving these structures, as seen in our Solar System with the gas giants. We reduce the JWST/MIRI data using spaceKLIP, and introduce new routines to mitigate the Brighter-Fatter effect and persistence. We do not detect any planet candidates, and all detected objects in the field-of-view are consistent with background stars or galaxies. However, by combining JWST mass limits, archival observational constraints, and astrometric accelerations, we rule out a significant portion of planet parameter space, placing tight constraints on the planets possibly responsible for these gaps. To interpret these results, we explore multiple gap-carving scenarios in discs, either massless or with non-zero mass, including clearing by in-situ planet(s), as well as shaping by inner planets through mean-motion or secular apsidal resonances. Finally, we conclude that the planets causing the proper motion anomaly in these systems must reside within the inner 20 au.

astro-ph.EP↗

arXiv2025

JWST/NIRCam observations of HD~92945 debris disk: An asymmetric disk with a gap

We present the first observations of the HD92945 debris disk obtained with JWST, targeting this nearby K0V star located at 21.54 pc from the Sun. High-contrast coronagraphic imaging was performed using JWST/NIRCam in the F200W and F444W filters. After subtracting the disk contribution through forward modeling by means of synthetic PSFs and MCMC optimizations, the residuals were analyzed to identify candidate point sources. From these, we derived contrast curves and constructed detection probability maps for substellar companions. The disk is clearly detected in both NIRCam filters and reveals a broad, inclined structure with a gap, consistent with previous scattered-light and ALMA observations. The modeling confirms the presence of a gap at ~80 au and shows a scale height and scattering properties compatible with a dynamically active disk. A significant brightness asymmetry is observed in the southwestern inner ring at both 2 and 4.4 {\mu}m, consistent with previous ALMA results. Observing this feature across different wavelengths and epochs strongly supports a scenario where one or more unseen planetary companions are perturbing the disk. No comoving sources are detected, and all candidate objects in the field are consistent with background stars or galaxies. The derived detection limits exclude planets more massive than ~0.4-0.5 MJ beyond 100 au and more massive than ~1 MJ beyond 20-40 au. This, in turn, rules out the possibility of a single planet placed beyond ~20 au as responsible for the astrometric signal observed by Gaia. These results, combined with the observed disk features, support a scenario in which a single or multiple sub-Jupiter planets dynamically shape the system through mechanisms such as secular apsidal resonances, providing a coherent explanation for the gap, the asymmetric brightness distribution and the astrometric signal.

astro-ph.EP↗

arXiv2025

Prospects for the formation of GW231123 from the AGN channel

The recent binary black hole (BBH) merger GW231123 consisted of the merger of two intermediate mass black holes (IMBH) which appear to have large spin magnitudes. Active galactic nuclei (AGN) are very promising environments for IMBH mergers and growth due to high escape velocities. Here we demonstrate how GW231123 can be produced in the AGN channel. Using the McFACTS code, we explore the impact of various choices of the black hole (BH) initial mass function (IMF) on predicted mass and spin magnitudes of BBH mergers from the AGN dynamical formation channel. By integrating the likelihood function for GW231123 with the detectable BBH population predicted from AGN using McFACTS, we demonstrate that GW231123 is consistent with a dynamical BBH merger from the AGN channel. We also postulate that the masses and spin magnitudes of GW231123 are most consistent with a merger of fourth and third generation BHs, for most choices of a segregated BH IMF and AGN lifetime.

gr-qc↗

arXiv2025

Suppression of ferromagnetism in van der Waals insulator due to pressure-induced layer stacking variation

Ferromagnetism in van der Waals insulators like CrBr3 is highly sensitive to structural modifications. We explore the pressure-driven structural and magnetic transformations of the van der Waals magnet CrBr3, establishing it as a model platform for phenomena emerging in layered vdW systems. Single-crystal X-ray diffraction revealed intrinsic trimorphism with two known phases (monoclinic and rhombohedral) and a so-far unreported trigonal phase. The paracrystal model well captures the coexistence of the rhombohedral and trigonal phases at ambient conditions. Increasing pressure drives the growth of the AA-stacked trigonal phase at the expense of the rhombohedral phase, which becomes undetectable above 8.4 GPa. Magnetization measurements provided the first direct evidence of a collapse of ferromagnetism above 5.8 GPa. This behavior is attributed to the increasing number of AFM-coupled Cr moments in AA stackings. Ab initio DFT calculations of electronic structure and atomistic simulations of finite-temperature magnetism corroborate the scenario.

cond-mat.mtrl-sci↗

arXiv2024

First Measurement of Correlated Charge Noise in Superconducting Qubits at an Underground Facility

We measure space- and time-correlated charge jumps on a four-qubit device, operating 107 meters below the Earth's surface in a low-radiation, cryogenic facility designed for the characterization of low-threshold particle detectors. The rock overburden of this facility reduces the cosmic ray muon flux by over 99% compared to laboratories at sea level. Combined with 4$\pi$ coverage of a movable lead shield, this facility enables quantifiable control over the flux of ionizing radiation on the qubit device. Long-time-series charge tomography measurements on these weakly charge-sensitive qubits capture discontinuous jumps in the induced charge on the qubit islands, corresponding to the interaction of ionizing radiation with the qubit substrate. The rate of these charge jumps scales with the flux of ionizing radiation on the qubit package, as characterized by a series of independent measurements on another energy-resolving detector operating simultaneously in the same cryostat with the qubits. Using lead shielding, we achieve a minimum charge jump rate of 0.19$^{+0.04}_{-0.03}$ mHz, almost an order of magnitude lower than that measured in surface tests, but a factor of roughly eight higher than expected based on reduction of ambient gammas alone. We operate four qubits for over 22 consecutive hours with zero correlated charge jumps at length scales above three millimeters.

quant-ph↗

arXiv2023

The effect of gravitational decoupling on constraining the mass and radius for the secondary component of GW190814 and other self-bound strange stars in f(Q)-gravity theory

Inspired by the conundrum of the gravitational event, GW190814 which brings to light the coalescence of a 23 $ M_{\odot}$ black hole with a yet to be determined secondary component, we look to modelling compact objects within the framework of $f(\mathcal{Q})$ gravity by employing the method of gravitational decoupling. We impose a quadratic equation of state (EOS) for the interior matter distribution which in the appropriate limit reduces to the MIT bag model. The governing field equations arising from gravitational decoupling bifurcates into the $\rho=\theta^0_0$ and $p_r=\theta^1_1$ sectors leading to two distinct classes of solutions. Both families of solutions are subjected to rigorous tests qualifying them to describe a plethora of compact objects including neutron stars, strange stars and the possible progenitor of the secondary component of GW190814. Using observational data of mass-radius relations for compact objects LMC X-4, Cen X-3, PSR J1614-2230 and PSR J0740+6620 we show that it is possible to generate stellar masses and radii beyond 2.0 $ M_{\odot}$ for neutron stars. Our findings reveal that the most { suitable and versatile model in this framework is the quadratic EOS}, which accounts for a range of low mass stars as well as typical stellar candidates describing the secondary component of GW190814.

gr-qc↗

arXiv2022

Direct discovery of the inner exoplanet in the HD206893 system. Evidence for deuterium burning in a planetary-mass companion

Long term precise radial velocity (RV) monitoring of the nearby star HD206893, as well as anomalies in the system proper motion, have suggested the presence of an additional, inner companion in the system. Here we describe the results of a multi-epoch search for the companion responsible for this RV drift and proper motion anomaly using the VLTI/GRAVITY instrument. Utilizing information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we report a high significance detection of the companion HD206893c over three epochs, with clear evidence for Keplerian orbital motion. Our astrometry with $\sim$50-100 $\mu$arcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7$^{+1.2}_{-1.0}$ M$_{\rm Jup}$ and an orbital separation of 3.53$^{+0.08}_{-0.06}$ au for HD206893c. Our fits to the orbits of both companions in the system utilize both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore derive an age of $155\pm15$ Myr. We find that theoretical atmospheric/evolutionary models incorporating deuterium burning for HD206893c, parameterized by cloudy atmospheres provide a good simultaneous fit to the luminosity of both HD206893B and c. In addition to utilizing long-term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part with Gaia astrometry. Utilizing Gaia astrometry is expected to be one of the primary techniques going forward to identify and characterize additional directly imaged planets. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form at ice-line orbital separations of 2-4\,au.

astro-ph.EP↗

arXiv2022

Snowmass 2021 Scintillating Bubble Chambers: Liquid-noble Bubble Chambers for Dark Matter and CE$\nu$NS Detection

The Scintillating Bubble Chamber (SBC) Collaboration is developing liquid-noble bubble chambers for the quasi-background-free detection of low-mass (GeV-scale) dark matter and coherent scattering of low-energy (MeV-scale) neutrinos (CE$\nu$NS). The first physics-scale demonstrator of this technique, a 10-kg liquid argon bubble chamber dubbed SBC-LAr10, is now being commissioned at Fermilab. This device will calibrate the background discrimination power and sensitivity of superheated argon to nuclear recoils at energies down to 100 eV. A second functionally-identical detector with a focus on radiopure construction is being built for SBC's first dark matter search at SNOLAB. The projected spin-independent sensitivity of this search is approximately $10^{-43}$ cm$^2$ at 1 GeV$/c^2$ dark matter particle mass. The scalability and background discrimination power of the liquid-noble bubble chamber make this technique a compelling candidate for future dark matter searches to the solar neutrino fog at 1 GeV$/c^2$ particle mass (requiring a $\sim$ton-year exposure with non-neutrino backgrounds sub-dominant to the solar CE$\nu$NS signal) and for high-statistics CE$\nu$NS studies at nuclear reactors.

physics.ins-det↗

arXiv2022

On The Generalisation of Henstock-Kurzweil Fourier Transform

In this paper, a generalised integral called the Laplace integral is defined on unbounded intervals, and some of its properties, including necessary and sufficient condition for differentiating under the integral sign, are discussed. It is also shown that this integral is more general than the Henstock-Kurzweil integral. Finally, the Fourier transform is defined using the Laplace integral, and its well-known properties are established.

math.CA↗

arXiv2021

Traversable wormhole models in $f(R)$ gravity

In this work, we analyze the wormhole solutions in $f(R)$ gravity. Specifically we sought for wormhole geometry solutions for the following three shape functions: (i) $b(r)=r_{0}+\rho_{0}r_{0}^{3}\ln\left(\frac{r_{0}}{r}\right)$, (ii) $b(r)=r_{0}+\gamma r_{0}\left(1-\dfrac{r_{0}}{r}\right)$, and (iii) $b(r)=\alpha +\beta r$, under some legitimate physical conditions on the parameters as well as constants involved here with in the shape functions. It is observed from the graphical plots that the behaviour of the physical parameters are interesting and viable.

gr-qc↗

arXiv2021

A Generalised Continuous Primitive Integral and Some of Its Applications

Using the Laplace derivative a Perron type integral, the Laplace integral, is defined. Moreover, it is shown that this integral includes Perron integral and to show that the inclusion is proper, an example of a function is constructed, which is Laplace integrable but not Perron integrable. Properties of integrals such as fundamental theorem of calculus, Hake's theorem, integration by parts, convergence theorems, mean value theorems, the integral remainder form of Taylor's theorem with an estimation of the remainder, are established. It turns out that concerning the Alexiewicz's norm, the space of all Laplace integrable functions is incomplete and contains the set of all polynomials densely. Applications are shown to Poisson integral, a system of generalised ordinary differential equations and higher-order generalised ordinary differential equation.

math.CA↗

arXiv2020

Phases and collective modes of bosons in a triangular lattice at finite temperature: A cluster mean field study

Motivated by the realization of Bose-Einstein condensates (BEC) in non-cubic lattices, in this work we study the phases and collective excitation of bosons with nearest neighbor interaction in a triangular lattice at finite temperature, using mean field (MF) and cluster mean field (CMF) theory. We compute the finite temperature phase diagram both for hardcore and softcore bosons, as well analyze the effect of correlation arising due to lattice frustration and interaction systematically using CMF method. A semi-analytic estimate of the transition temperatures between different phases are derived within the framework of MF Landau theory, particularly for hardcore bosons. Apart from the usual phases such as density waves (DW) and superfluid (SF), we also characterize different supersolids (SS). These phases and their transitions at finite temperature are identified from the collective modes. The low lying excitations, particularly Goldstone and Higgs modes of the supersolid can be detected in the ongoing cold atom experiments.

cond-mat.quant-gas↗

arXiv2020

High spin states of $^{204}$At: isomeric states and shears band structure

High-spin states of neutron deficient Trans-Lead nucleus $^{204}$At were populated up to $\sim 8\,{\rm MeV}$ excitation through the $^{12}$C + $^{197}$Au fusion evaporation reaction. Decay of the associated levels through prompt and delayed $\gamma$-ray emissions were studied to evaluate the underlying nuclear structure. The level scheme, which was partly known, was extended further. An isomeric $16^+$ level with observed lifetime $\tau=52 \pm 5\, {\rm ns}$, was established from our measurements. Attempts were made to interpret the excited states based on multi quasiparticle and hole structures involving $2f_{5/2}$, $1h_{9/2}$, and $1i_{13/2}$ shell model states, along with moderate core excitation. Magnetic dipole band structure over the spin parity range:~$16^+ - 23^+$ was confirmed and evaluated in more detail, including the missing cross-over $E2$ transitions. Band-crossing along the shears band was observed and compared with the evidence of similar phenomena in the neighbouring neutron deficient $^{202}$Bi, $^{205}$Rn isotones and the $^{203}$At isotope. Based on comparison of the measured $B(M1)/B(E2)$ values for transitions along the band with the semiclassical model based estimates, the shears band of $^{204}$At was established along with the level scheme.

nucl-ex↗