arXiv subjects

Sourav Mondal

Publications and source records attributed to Sourav Mondal.

At least 19 recordsLinked to original sources

arXiv2026

Constraining Reheating Temperature, Inflaton-SM Coupling and Dark Matter Mass in Light of ACT DR6 Observations

We explore the phenomenological implications of the latest Atacama Cosmology Telescope (ACT) DR6 observations, in combination with Planck 2018, BICEP/Keck 2018, and DESI, on the physics of inflation and post-inflationary reheating. We focus on the $α$-attractor class of inflationary models (both E- and T-models) and consider two reheating scenarios: perturbative inflaton ($ϕ$) decay ($ϕ\rightarrow bb$) and inflaton annihilation ($ϕϕ\rightarrow bb$) into Standard Model (SM) bosonic particles ($b$). By solving the Boltzmann equations, we derive bounds on key reheating parameters, including the reheating temperature, the inflaton equation of state (EoS), and the inflaton-SM coupling, in light of ACT data. To accurately constrain the coupling, we incorporate the Bose enhancement effect in the decay width. To ensure the validity of our perturbative approach, we also identify the regime where nonperturbative effects, such as parametric resonance, become significant. Additionally, we include indirect constraints from primordial gravitational waves (PGWs), which can impact the effective number of relativistic species, $ΔN_{\rm eff}$. These constraints further bound the reheating temperature, particularly in scenarios with a stiff EoS. Finally, we analyze dark matter (DM) production through purely gravitational interactions during reheating and determine the allowed mass ranges consistent with the constrained reheating parameter space and recent ACT data.

hep-ph↗

arXiv2026

Universal characterization of Efimovian $D^0 nn$ System via Faddeev Techniques

We demonstrate remnant structural universality in a putative S-wave $2n$-halo-bound $D^0nn$ system in the $J=0, T=3/2$ channel by invoking the zero-coupling limit (ZCL), which eliminates sub-threshold decay channels. Within this framework, we evaluate the one- and two-body matter density form factors, their associated root mean-square radii, and the $n$-$D^0$-$n$ opening angle. Our analysis is carried out at leading order using a quantum mechanical Faddeev technique in the momentum representation. Employing Jacobi momenta, we construct a complete partial-wave basis to expand the full three-body $D^0nn$ wave function across distinct rearrangement channels. Projection onto this basis yields a coupled set of Faddeev integral equations that govern the multiple-scattering dynamics of the constituent coupled spin-isospin subsystems. By introducing short-range separable interactions and expressing the two-body scattering amplitudes via spectator functions, we establish a direct correspondence with the familiar Skornyakov-Ter-Martirosyan equations from halo-EFT approach at leading order. A regulator-dependent analysis highlights the Efimov-like character of the three-body observables, with ground state properties exhibiting marked sensitivity to cutoff variations. However, the inclusion of a three-body force suppresses this dependence, as expected from renormalization-group invariance. We thereby conclude that, for sufficiently shallow three-body binding, the $D^0nn$ system in the ZCL exhibits a universal halo-bound structure. The subtle implications of range-like corrections at LO are addressed at a qualitative level in this analysis.

nucl-th↗

arXiv2026

Freeze-in and freeze-out production of Higgs portal Majorana fermionic dark matter during and after reheating

In this paper, we investigate the production of Majorana fermionic dark matter (DM) via the Higgs portal, considering both freeze-in and freeze-out mechanisms during and after the post-inflationary reheating phase. We assume that the Universe is reheated through the decay of the inflaton ($ϕ$) into a pair of fermions $f$ and $\bar f$ via the interaction $y\,ϕ\,\bar f\,f$, where $y$ is the dimensionless Yukawa coupling. Our analysis focuses on how the non-standard evolution of the Hubble expansion rate and the thermal bath temperature during reheating influence DM production. Additionally, we examine the impact of electroweak symmetry breaking (EWSB), distinguishing between scenarios where DM freeze-in or freeze-out occurs before or after EWSB. We further explore the viable DM parameter space and its compatibility with current and future detection experiments, including XENONnT, LUX-ZEPLIN (LZ), XLZD, and collider searches. Moreover, we incorporate constraints from the Lyman-$α$ bound to ensure consistency with small-scale structure formation.

hep-ph↗

arXiv2025

A practical approach to perturbative corrections to few-body observables

We formulate two methods to facilitate the calculation of perturbative corrections to quantum few-body observables. Both techniques are designed for a numerical realization in combination with any tool that obtains either the entire spectrum or solely the eigenvalues of an operator corresponding to the observable of interest. We exemplify these methods in the context of the nuclear contact theory without pions (Pionless EFT) and benchmark them in the deuteron channel with available analytical, field-theoretical calculations, as well as in the triton and 3-helium channels through earlier extractions within the dibaryon formalism, where in all three systems the point-proton root-mean-square charge radius (rms) was the perturbed observable of choice. Beyond these $A\leq3$ consistency and accuracy checks, we employ the numerical methods to predict the rms of the 4-helium nuclear ground state to assess three different ways of integrating the Coulomb interaction into Pionless EFT. By comparing the respective results at leading and next-to-leading order for 3- and 4-helium, we find that the uncertainty due to the strong, short-range interaction is significantly larger compared with that due to the long-range Coulomb interaction for both bound states with their different binding momenta. Thereby, we provide strong support for simplifying extractions of bound-state observables by shutting off any Coulomb interaction if the strong part of the potential is considered only up to first order in the effective range expansion.

nucl-th↗

arXiv2025

Enabling Immersive XR Collaborations over FTTR Networks (Invited)

Fiber-To-The-Room is a potential solution to achieve in-premise extended reality collaborations. This paper explores predictive bandwidth allocation and seamless handover schemes over FTTR, showing high-quality immersive experience for in-premise collaborations can be achieved. \c{opyright} 2025 The Author(s).

cs.NI↗

arXiv2025

User Head Movement-Predictive XR in Immersive H2M Collaborations over Future Enterprise Networks

The evolution towards future generation of mobile systems and fixed wireless networks is primarily driven by the urgency to support high-bandwidth and low-latency services across various vertical sectors. This endeavor is fueled by smartphones as well as technologies like industrial internet of things, extended reality (XR), and human-to-machine (H2M) collaborations for fostering industrial and social revolutions like Industry 4.0/5.0 and Society 5.0. To ensure an ideal immersive experience and avoid cyber-sickness for users in all the aforementioned usage scenarios, it is typically challenging to synchronize XR content from a remote machine to a human collaborator according to their head movements across a large geographic span in real-time over communication networks. Thus, we propose a novel H2M collaboration scheme where the human's head movements are predicted ahead with highly accurate models like bidirectional long short-term memory networks to orient the machine's camera in advance. We validate that XR frame size varies in accordance with the human's head movements and predict the corresponding bandwidth requirements from the machine's camera to propose a human-machine coordinated dynamic bandwidth allocation (HMC-DBA) scheme. Through extensive simulations, we show that end-to-end latency and jitter requirements of XR frames are satisfied with much lower bandwidth consumption over enterprise networks like Fiber-To-The-Room-Business. Furthermore, we show that better efficiency in network resource utilization is achieved by employing our proposed HMC-DBA over state-of-the-art schemes.

cs.NI↗

arXiv2025

Scalable Coordinated Learning for H2M/R Applications over Optical Access Networks (Invited)

One of the primary research interests adhering to next-generation fiber-wireless access networks is human-to-machine/robot (H2M/R) collaborative communications facilitating Industry 5.0. This paper discusses scalable H2M/R communications across large geographical distances that also allow rapid onboarding of new machines/robots as $\sim72\%$ training time is saved through global-local coordinated learning.

cs.NI↗

arXiv2024

The spin-phonon relaxation mechanism of single-molecule magnets in the presence of strong exchange coupling

Magnetic relaxation in coordination compounds is largely dominated by the interaction of the spin with phonons. Large zero-field splitting and exchange coupling values have been empirically found to strongly suppress spin relaxation and have been used as the main guideline for designing new molecular compounds. Although a comprehensive understanding of spin-phonon relaxation has been achieved for mononuclear complexes, only a qualitative picture is available for polynuclear compounds. Here we fill this critical knowledge gap by providing a full first-principle description of spin-phonon relaxation in an air-stable Co(II) dimer with both large single-ion anisotropy and exchange coupling. Simulations reproduce the experimental relaxation data with excellent accuracy and provide a microscopic understanding of Orbach and Raman relaxation pathways and their dependency on exchange coupling, zero-field splitting, and molecular vibrations. Theory and numerical simulations show that increasing cluster nuclearity to just four cobalt units would lead to a complete suppression of Raman relaxation. These results hold a general validity for single-molecule magnets, providing a deeper understanding of their relaxation and revised strategies for their improvement.

cond-mat.mtrl-sci↗

arXiv2024

Scale-(in)dependence in quantum 4-body scattering

We investigate the multi-channel 4-body scattering system using regularized 2- and 3-body contact interactions. The analysis determines the sensitivity of bound-state energies, scattering phase shifts and cross sections on the cutoff parameter ($λ$), and the energy gaps between scattering thresholds. The latter dependency is obtained with a 2-body scale fixed to an unnaturally large value and a floating 3-body parameter. Specifically, we calculate the binding energies of the shallow 3- and 4-body states, dimer-dimer and trimer-atom scattering lengths, and the trimer-atom to dimer-dimer reaction rates. Employing a potential renormalized by a large 2-body scattering length and a 3-body scale, we find all calculated observables to remain practically constant over the range $6\textrm{fm}^{-2}<λ<10\textrm{fm}^{-2}$. Divergences in scattering lengths emerge for critical 3-body parameters at which thresholds are degenerate. Such threshold effects are found to be independent of the regulator cutoff. Furthermore, at those critical points where the dimer-dimer and trimer-atom thresholds overlap, we predict an enhancement of the inelastic over the elastic scattering event. Such an inversion between elastic- and rearrangement-collision probabilities indicates a strong sensitivity of the 4-body reaction dynamics on the 3-body parameter at finite 2-body scale. This phenomenon is absent in earlier studies which differ in the renormalization scheme. As this discrepancy arises for all considered cutoffs, a more comprehensive parametrization of short-distance structure is necessary: sole cutoff variation does not reveal non-perturbative change in reaction rates conjectured to be due to a combined effect of the finite 2-body range and the specific choice for the 3-body parameter.

nucl-th↗

arXiv2023

Spin-vibronic dynamics in open-shell systems beyond the spin Hamiltonian formalism

Vibronic coupling has a dramatic influence over a large number of molecular processes, ranging from photo-chemistry, to spin relaxation and electronic transport. The simulation of vibronic coupling with multi-reference wavefunction methods has been largely applied to organic compounds, and only early efforts are available for open-shell systems such as transition metal and lanthanide complexes. In this work, we derive a numerical strategy to differentiate the molecular electronic Hamiltonian in the context of multi-reference ab initio methods and inclusive of spin-orbit coupling effects. We then provide a formulation of open quantum system dynamics able to predict the time evolution of the electrons' density matrix under the influence of a Markovian phonon bath up to fourth-order perturbation theory. We apply our method to Co(II) and Dy(III) molecular complexes exhibiting long spin relaxation times and successfully validate our strategy against the use of an effective spin Hamiltonian. Our study shed light on the nature of vibronic coupling, the importance of electronic excited states in spin relaxation, and the need for high-level computational chemistry to quantify it.

physics.chem-ph↗

arXiv2023

Fairness Guaranteed and Auction-based x-haul and Cloud Resource Allocation in Multi-tenant O-RANs

The open-radio access network (O-RAN) embraces cloudification and network function virtualization for base-band function processing by dis-aggregated radio units (RUs), distributed units (DUs), and centralized units (CUs). These enable the cloud-RAN vision in full, where multiple mobile network operators (MNOs) can install their proprietary or open RUs, but lease on-demand computational resources for DU-CU functions from commonly available open-clouds via open x-haul interfaces. In this paper, we propose and compare the performances of min-max fairness and Vickrey-Clarke-Groves (VCG) auction-based x-haul and DU-CU resource allocation mechanisms to create a multi-tenant O-RAN ecosystem that is sustainable for small, medium, and large MNOs. The min-max fair approach minimizes the maximum OPEX of RUs through cost-sharing proportional to their demands, whereas the VCG auction-based approach minimizes the total OPEX for all resources utilized while extracting truthful demands from RUs. We consider time-wavelength division multiplexed (TWDM) passive optical network (PON)-based x-haul interfaces where PON virtualization technique is used to flexibly provide optical connections among RUs and edge-clouds at macro-cell RU locations as well as open-clouds at the central office locations. Moreover, we design efficient heuristics that yield significantly better economic efficiency and network resource utilization than conventional greedy resource allocation algorithms and reinforcement learning-based algorithms.

cs.NI↗

arXiv2023

Spin-phonon decoherence in solid-state paramagnetic defects from first principles

Paramagnetic defects in diamond and hexagonal boron nitride possess a unique combination of spin and optical properties that make them prototypical solid-state qubits. Despite the coherence of these spin qubits being critically limited by spin-phonon relaxation, a full understanding of this process is not yet available. Here we apply ab initio spin dynamics simulations to this problem and quantitatively reproduce the experimental temperature dependence of spin relaxation time and spin coherence time. We demonstrate that low-frequency two-phonon modulations of the zero-field splitting are responsible for spin relaxation and decoherence, and point to the nature of vibrations in 2-dimensional materials as the culprit for their shorter coherence time. These results provide a novel interpretation to spin-phonon decoherence in solid-state paramagnetic defects, offer a new strategy to correctly interpret experimental results, and pave the way for the accelerated design of new spin qubits.

quant-ph↗

arXiv2022

Unravelling the contributions to spin-lattice relaxation in Kramers single-molecule magnets

The study of how spin interacts with lattice vibrations and relaxes to equilibrium provides unique insights on its chemical environment and the relation between electronic structure and molecular composition. Despite its importance for several disciplines, ranging from magnetic resonance to quantum technologies, a convincing interpretation of spin dynamics in crystals of magnetic molecules is still lacking due to the challenging experimental determination of the correct spin relaxation mechanism. We apply ab initio spin dynamics to a series of twelve coordination complexes of Co(II) and Dy(III) ions selected among $\sim$240 compounds that largely cover the literature on single-molecule magnets and well represent different regimes of spin relaxation. Simulations reveal that the Orbach spin relaxation rate of known compounds mostly depends on the ions' zero-field splitting and little on the details of molecular vibrations. Raman relaxation is instead found to be also significantly affected by the features of low-energy phonons. These results provide a complete understanding of the factors limiting spin lifetime in single-molecule magnets and revisit years of experimental investigations by making it possible to transparently distinguish Orbach and Raman relaxation mechanisms.

cond-mat.mtrl-sci↗

arXiv2022

Statistical analysis of proton induced reactions to generate recommended data for the production of medical radio-isotopes

Radio-isotopes produced via proton induced reaction holds special significance regarding nuclear medicine, astrophysical p-process, theragnostic and diagnostic processes. $^{76}$Br, $^{80m}$Br and $^{61}$Cu are positron emitter and they are useful in the functional studies via Positron Emission Tomography (PET), whereas $^{77}$Br bears the potential for the application in Single Photon Emission Computed Tomography (SPECT) which involves electron capture process. PET and SPECT have been in high application in medical physics, diagnostics, therapy and nuclear medicine. $^{99m}$Tc and $^{64}$Cu are two popular radionuclide which play important role in nuclear medicine, currently being used in bio-medical physics, bone scan, modern imaging, blood pool leveling, oncology and diagnosis of copper related diseases. This paper focus on the generation of recommended nuclear reaction cross sections for the production of some useful medical radio-isotopes using the experimental datasets obtained from EXFOR database and simulated datasets from nuclear reaction model codes TALYS-1.95 and EMPIRE-3.1.1. 95\% confidence interval has been implemented to ensure confidence and precision.

nucl-th↗

arXiv2022

Optical Front/Mid-haul with Open Access-Edge Server Deployment Framework for Sliced O-RAN

The fifth-generation of mobile radio technologies is expected to be agile, flexible, and scalable while provisioning ultra-reliable and low-latency communication (uRLLC), enhanced mobile broadband (eMBB), and massive machine type communication (mMTC) applications. An efficient way of implementing these is by adopting cloudification, network function virtualization, and network slicing techniques with open-radio access network (O-RAN) architecture where the base-band processing functions are disaggregated into virtualized radio unit (RU), distributed unit (DU), and centralized unit (CU) over front/mid-haul interfaces. However, cost-efficient solutions are required for designing front/mid-haul interfaces and time-wavelength division multiplexed (TWDM) passive optical network (PON) appears as a potential candidate. Therefore, in this paper, we propose a framework for the optimal placement of RUs based on long-term network statistics and connecting them to open access-edge servers for hosting the corresponding DUs and CUs over front/mid-haul interfaces while satisfying the diverse QoS requirements of uRLLC, eMBB, and mMTC slices. In turn, we formulate a two-stage integer programming problem and time-efficient heuristics for users to RU association and flexible deployment of the corresponding DUs and CUs. We evaluate the O-RAN deployment cost and latency requirements with our TWDM-PON-based framework against urban, rural, and industrial areas and show its efficiency over the optical transport network (OTN)-based framework.

cs.NI↗

arXiv2022

CCOMPASSION: A Hybrid Cloudlet Placement Framework over Passive Optical Access Networks

Cloud-based computing technology is one of the most significant technical advents of the last decade and extension of this facility towards access networks by aggregation of cloudlets is a step further. To fulfill the ravenous demand for computational resources entangled with the stringent latency requirements of computationally-heavy applications related to augmented reality, cognitive assistance and context-aware computation, installation of cloudlets near the access segment is a very promising solution because of its support for wide geographical network distribution, low latency, mobility and heterogeneity. In this paper, we propose a novel framework, Cloudlet Cost OptiMization over PASSIve Optical Network (CCOMPASSION), and formulate a nonlinear mixed-integer program to identify optimal cloudlet placement locations such that installation cost is minimized whilst meeting the capacity and latency constraints. Considering urban, suburban and rural scenarios as commonly-used network deployment models, we investigate the feasibility of the proposed model over them and provide guidance on the overall cloudlet facility installation over optical access network. We also study the percentage of incremental energy budget in the presence of cloudlets of the existing network. The final results from our proposed model can be considered as fundamental cornerstones for network planning with hybrid cloudlet network architectures.

cs.NI↗

arXiv2022

A Min-Max Fair Resource Allocation Framework for Optical x-haul and DU/CU in Multi-tenant O-RANs

The recently proposed open-radio access network (O-RAN) architecture embraces cloudification and network function virtualization techniques to perform the base-band function processing by dis-aggregated radio units (RUs), distributed units (DUs), and centralized units (CUs). This enables the cloud-RAN vision in full, where mobile network operators (MNOs) could install their own RUs, but then lease on-demand computational resources for the processing of DU and CU functions from commonly available open-cloud (O-Cloud) servers via open x-haul interfaces due to variation of load over the day. This creates a multi-tenant scenario where multiple MNOs share networking as well as computational resources. In this paper, we propose a framework that dynamically allocates x-haul and DU/CU resources in a multi-tenant O-RAN ecosystem with min-max fairness guarantees. This framework ensures that a maximum number of RUs get sufficient resources while minimizing the OPEX for their MNOs. Moreover, in order to provide an access network architecture capable of sustaining low-latency and high capacity between RUs and edge-computing devices, we consider time-wavelength division multiplexed (TWDM) passive optical network (PON)-based x-haul interfaces where the PON virtualization technique is used to provide a direct optical connection between end-points. This creates a virtual mesh interconnection among all the nodes such that the RUs can be connected to the Edge-Clouds at macro-cell RU locations as well as to the O-Cloud servers at the central office locations. Furthermore, we analyze the system performance with our proposed framework and show that MNOs can operate with a better cost-efficiency than baseline greedy resource allocation with uniform cost-sharing.

cs.NI↗

arXiv2022

Lattice QCD Equation of State for Nonvanishing Chemical Potential by Resumming Taylor Expansion

Taylor expansion in powers of baryon chemical potential ($μ_B$) is an oft-used method in lattice QCD to compute QCD thermodynamics for $μ_B>0$. Based only upon the few known lowest order Taylor coefficients, it is difficult to discern the range of $μ_B$ where such an expansion around $μ_B=0$ can be trusted. We introduce a resummation scheme for the Taylor expansion of the QCD equation of state in $μ_B$ that is based on the $n$-point correlation functions of the conserved current ($D_n$). The method resums the contributions of the first $N$ correlation function $D_1,\dots,D_N$ to the Taylor expansion of the QCD partition function to all orders in $μ_B$. We show that the resummed partition function is an approximation to the reweighted partition function at $μ_B\ne0$. We apply the proposed approach to high-statistics lattice QCD calculations using 2+1 flavors of Highly Improved Staggered Quarks with physical quark masses on $32^3\times8$ lattices and for temperatures $T\approx145$-176 MeV. We demonstrate that, as opposed to the Taylor expansion, the resummed version not only leads to improved convergence but also reflects the zeros of the resummed partition function and severity of the sign problem, leading to its eventual breakdown. We also provide a generalization of our scheme to include resummation of powers of temperature and quark masses in addition to $μ_B$, and show that the alternative expansion scheme of [S. Borsányi et al., Phys. Rev. Lett. 126, 232001 (2021).] is a special case of this generalized resummation.

hep-lat↗