arXiv subjects

Sabyasachi Chakraborty

Publications and source records attributed to Sabyasachi Chakraborty.

At least 19 recordsLinked to original sources

arXiv2026

Soft Collinear Effective Theory for Heavy QCD Axions

We develop a soft-collinear effective theory (SCET) framework for heavy QCD axion, considering two low-energy realizations and taking $B\to Ka$ as a benchmark mode. In the first realization, $aG\widetilde G$ is assumed to be the only independent axion interaction at the scale $μ\sim m_b$. We show that eliminating the redundant flavor-changing derivative-gluon operator in the weak effective theory generates a new dimension-seven axion operator identified as $\mathrm{O}_{\partial ag}$. We match this operator onto SCET and derive the corresponding leading-power soft and spectator-scattering contributions to $B\to Ka$. We obtain a factorized expression for the spectator contribution in terms of perturbative hard kernels and the $B$- and $K$-meson light-cone distribution amplitudes. The spectator contribution arises at the same order in the power expansion as the soft-overlap term and amounts to approximately $25\%$ of the soft contribution. In the second realization, the Wilson coefficient of $aG\widetilde G$ is assumed to be present above the electroweak scale. Renormalization-group evolution and matching then induce a direct $b\to sa$ operator, which subsequently results in a dominant soft form-factor contribution, whereas the gluonic spectator term turns out to be numerically subleading ($\sim 6-7\%$). We thus identify the conditions under which spectator scattering becomes relevant for heavy-axion production in rare $B$-meson decays. Finally, we derive the corresponding bounds on the axion decay constant $f_a$ for both realizations and compare their phenomenological implications.

hep-ph↗

arXiv2026

Hilbert Series of Pseudoscalar Mesons: Operators and Sum Rules

We construct the complete non-redundant basis of operators built from pseudoscalar mesons using the Hilbert series method, subject to the global flavor symmetry $SU(3)_L \times SU(3)_R \times SU(2)_{L_H} \times SU(2)_{R_H}$, together with the underlying shift symmetry. The SM weak interactions are incorporated systematically by promoting the CKM matrix elements to spurion fields transforming under the global symmetry. The resulting operator basis provides a model-independent parametrization of two- and three-body weak decay amplitudes of heavy mesons, with the corresponding Wilson coefficients serving as reduced hadronic amplitudes. We demonstrate that all amplitude sum rules follow directly from the structure of the operator basis and propose an unfolding procedure that connects the effective operators to their possible ultraviolet origins. Our framework reproduces the known flavor relations while predicting additional identities arising from the symmetry-constrained operator basis.

hep-ph↗

arXiv2026

Marked vertex search on disordered graphs with Rosenzweig-Porter phases

Quantum marked vertex search algorithms are known to outperform their classical counterparts, yet their behavior in the presence of disorder remains largely unexplored. Here, we address this gap by studying marked vertex search on disordered random graphs. To introduce disorder, we implement the Rosenzweig-Porter (RP) model, a random matrix ensemble with tunable ergodic, non-ergodic extended, and localized phases, on Erdős-Rényi (ER) graphs. This produces a doubly random system where ER graph connectivity randomizes which interactions exist, while RP disorder controls their strength and `on-site' potentials, providing a two-parameter framework to study quantum dynamics on disordered networks. First, we show that the characteristic Wigner-Dyson-to-Poisson spectral crossover of the RP ensemble survives under graph constraints across the sparse-to-dense range, and we derive an analytical estimate for the finite-size localization boundary that shifts systematically with the graph edge probability $p$, consistent with a resonant-hybridization argument. Thereafter, using this disordered graph ensemble, we study the marked vertex search problem and find that search performance tracks the underlying quantum phase directly. Counterintuitively, the ergodic phase, despite supporting fast transport, yields lower success probability than the localized phase, which achieves high success probability at the cost of significantly longer search times. These results establish a direct and quantitative link between random matrix disorder on graphs and the performance of continuous-time quantum walk search, and suggest that disorder, rather than being merely an obstacle, can be exploited as a tunable parameter in quantum search protocols.

quant-ph↗

arXiv2026

Quantum circuit model for continuous-time quantum walks on random graphs

Quantum-circuit implementations of continuous-time quantum walks (CTQWs) can provide an efficient route to model graph-based algorithms. However, constructing circuits that faithfully reproduce CTQW dynamics across arbitrary graphs remains a major challenge. In this work, we introduce a Laplacian partitioning algorithm (LPA) that enables an efficient and scalable quantum-circuit realization of CTQWs on random graphs. A common algorithm to simulate a general graph (of size $N = 2^n$ for $n$ qubits) on a quantum circuit is based on Pauli decomposition of the graph Hamiltonian, which can yield $O(4^n)$ terms, and require $O(N^2\log N)$ time for coefficient computation. In contrast, our LPA uses $O(2^n)$ terms, in $O(N^2)$ time. Our circuit provides a graph-agnostic framework for CTQWs, implemented via a Trotter-Suzuki product formula and confirming error scaling consistent with theoretical Trotter error bounds. To further test the circuit performance, we study the localization behavior of the CTQW. In our case, localization originates from Laplacian spectral degeneracies rather than disorder (Anderson-type), and our circuit faithfully reproduces these localization phenomena and spectral structure for a random graphs with high accuracy.

quant-ph↗

arXiv2026

A Phenomenological Model of Mesons for Charged Current Weak Decays

We propose a phenomenological model of pseudo scalar mesons to describe charged-current weak decays of heavy-light mesons. The approach combines chiral symmetry in the light sector with heavy-quark flavor symmetry, while Cabibbo--Kobayashi--Maskawa (CKM) matrix elements are incorporated as spurions that encode explicit symmetry breaking. Restricting to charged-current interactions, we systematically organize the leading-order current-current operators at dimension six and identify the relevant operator structures governing fully-leptonic, semi-leptonic, and hadronic decays. This framework reproduces known heavy-quark scaling relations for decay constants and form factors in agreement with expectations from heavy quark effective theory, providing nontrivial consistency checks. Operators responsible for hadronic transitions are further classified into double-trace operators and single-trace operators. These single traces, interestingly, often capture several higher order corrections, non-factorizable effects etc. We check for consistencies for both single-trace and double-trace operators demanding that the resulting amplitudes should satisfy established isospin sum rules. As an application, we analyze the decay modes $B\to K + η_{c} / η^{\prime}/ η$. We find that these processes receive contributions from a host of non-trivial processes such as mixing between various states, non-perturbative QCD parameters such as the heavy quark condensates, non-factorizable effects, etc, apart from the straightforward perturbative $W$ exchange diagrams in the quark picture. Our set-up neatly captures all of these effects. The phenomenological model we provide here is a symmetry-guided, hadron-level description of charged-current processes and offers a complementary perspective to conventional quark-level approaches, with a natural avenue for incorporating non-factorizable effects.

hep-ph↗

arXiv2026

Axion EFT in the BMHV Scheme: Flavor Currents, Evanescent Operators and Ward Identities

We present a systematic analysis of axion effective field theory within the Breitenlohner-Maison-`t Hooft-Veltman (BMHV) scheme, focusing on the renormalization of fermionic dimension-five operators and the associated chiral flavor currents. In this framework, the non-anticommuting nature of $γ_5$ in $d \neq 4$ dimensions leads to violations of naive Ward identities through the emergence of evanescent operators. We derive the bare and renormalized Ward identities for chiral currents, explicitly identifying the equation-of-motion and evanescent operator contributions. Using diagrammatic calculations, we verify the validity of these identities up to two-loop order $\mathcal{O}(α_s^2)$, including both pole and finite terms. We demonstrate how evanescent operators mix into physical operators and determine the finite renormalization required to restore four-dimensional Ward identities, recovering the expected structure of axial current renormalization and the anomaly. Our results provide a consistent and transparent framework for multi-loop computations in axion EFT and highlight the essential role of evanescent operators in maintaining scheme consistency.

hep-ph↗

arXiv2025

A comprehensive study of ALPs from $B$-decays

We present a comprehensive study of axion-like particles (ALPs) through flavor changing neutral current processes, such as $B\to K a$ followed by $a\to\text{hadronic}, γγ,μ^+μ^-$ channels. Our generic framework encompasses different ultraviolet scenarios similar to KSVZ, DFSZ and flavorful axions etc. Starting from the effective Lagrangian written at the high scale, we compute the anomalous dimension matrix, taking into account all one-loop and relevant two-loop contributions. The latter is most important for the KSVZ and heavy QCD axion scenarios. We recognized that such two-loop diagrams can have both ultraviolet (UV) and infrared (IR) divergences. We show explicitly that UV divergences cancel by inserting appropriate counterterms, which are new operators involving the axion field and required to be present at the UV itself, to renormalize the theory. On the other hand, the cancellation of IR divergences is subtle and demonstrated through matching with the effective theory at the electroweak scale. We also utilize chiral perturbation theory and vector meson dominance framework to compute the decay and branching fractions of the ALP pertaining to our framework. We find that for KSVZ-like scenario, axion decay constant, $f_a \lesssim 1$ TeV can be ruled out. The bound becomes stronger for the DFSZ and Flaxion-like models, reaching upto $10^4$ TeV and $10^6$ TeV, respectively. We also provide projections on the parameter space based on 3 ab$^{-1}$ data from Belle II and 300 fb$^{-1}$ data from LHCb.

hep-ph↗

arXiv2025

Scalable quantum circuit simulation of a chaotic Ising chain

The recent advancements in out-of-time-ordered correlator (OTOC) measurements have provided a promising pathway to explore quantum chaos and information scrambling. However, despite recent advancements, their experimental realization remains challenging due to the complexity of implementing backward time evolution. Here, we present a scalable quantum circuit combined with the interferometric protocol, offering a more efficient framework for OTOC measurement. Using this method, we simulate commutator growth in integrable and chaotic regimes of a 9-qubit Ising chain. Our Trotterized circuit achieves errors below $10^{-11}$ with 4th-order Trotterization and performs well even with lower-order Trotterization approximations. We believe, this approach paves the way for studying information dynamics, highly entangled quantum systems, and complex observables efficiently.

quant-ph↗

arXiv2024

Scalable quantum circuits for exponential of Pauli strings and Hamiltonian simulations

In this paper, we design quantum circuits for the exponential of scaled $n$-qubit Pauli strings using single-qubit rotation gates, Hadamard gate, and CNOT gates. A key result we derive is that any two Pauli-string operators composed of identity and $X$ gates are permutation similar, and the corresponding permutation matrices are product of CNOT gates, with the $n$-th qubit serving as the control qubit. Consequently, we demonstrate that the proposed circuit model for exponential of any Pauli-string is implementable on low-connected quantum hardware and scalable i.e. quantum circuits for $(n+1)$-qubit systems can be constructed from $n$-qubit circuits by adding additional quantum gates and the extra qubit. We then apply these circuit models to approximate unitary evolution for several classes of Hamiltonians using the Suzuki-Trotter approximation. These Hamiltonians include $2$-sparse block-diagonal Hamiltonians, Ising Hamiltonians, and both time-independent and time-dependent Random Field Heisenberg Hamiltonians and Transverse Magnetic Random Quantum Ising Hamiltonians. Simulations for systems of up to 18 qubits show that the circuit approximation closely matches the exact evolution, with errors comparable to the numerical Trotterization error. Finally, we consider noise models in quantum circuit simulations to account for gate implementation errors in NISQ computers and observe that the noisy simulation closely resembles the noiseless one when gate and idle errors are on the order of $O(10^{-3})$ or smaller.

quant-ph↗

arXiv2024

Feasibility of ultrarelativistic bubbles in SMEFT

A first order electroweak phase transition probes physics beyond the Standard Model on multiple frontiers and therefore is of immense interest for theoretical exploration. We conduct a model-independent study of the effects of relevant dimension 6 and dimension 8 operators, of the Standard Model effective field theory, on electroweak phase transition. We use a thermally corrected and renormalization group improved potential and study its impact on nucleation temperature. We then outline bubble dynamics that lead to ultrarelativistic bubble wall velocities which are mainly motivated from the viewpoint of gravitational wave detection. We highlight the ranges of the Wilson coefficients that give rise to such bubble wall velocities and predict gravitational wave spectra generated by such transitions which can be tested in future experiments.

hep-ph↗

arXiv2024

Anomaly induced cooling of Neutron Stars: A Standard Model contribution

Young neutron stars cool via the emission of neutrinos from their core. A precise understanding of all the different processes producing neutrinos in the hot and degenerate matter is essential for assessing the cooling rate of such stars. The main Standard Model processes contributing to this effect are $ν$ bremsstrahlung, mURCA among others. In this paper, we investigate another Standard Model process initiated by the Wess-Zumino-Witten term, leading to the emission of neutrino pairs via $Nγ\to Nν\barν$. We find that for proto-neutron stars, such processes, with degenerate neutrons, can be comparable and even dominate over the prototypical and well-known cooling mechanisms.

hep-ph↗

arXiv2024

Photo-production of axions in Supernovae

Compact stellar objects like supernovae and neutron stars are believed to cool by emitting axions predominantly via axion bremsstrahlung ($NN \to NNa$), pion conversion ($π^- p^+ \to N a$) and photo-production ($γN \to N a$). In this paper, we study in detail the photo-production channel, from the unavoidable anomaly induced Wess-Zumino-Witten term $\propto ε^{μναβ}\, F_{μν}\, \partial_αa \, ω_β$ in conjunction with the low energy pion photo-production data. We found that for heavier axions, i.e., $m_a\sim\mathcal{O}(100)$ MeV, photo-production processes can be dominant compared to the usual axion emission processes. In addition, the spectrum of axions emitted in the process is significantly harder than those originating from bremsstrahlung.

hep-ph↗

arXiv2023

Stereo-Electronic Factors Influencing the Stability of Hydroperoxyalkyl Radicals: Transferability of Chemical Trends across Hydrocarbons and ab initio Methods

The hydroperoxyalkyl radicals (.QOOH) are known to play a significant role in combustion and tropospheric processes, yet their direct spectroscopic detection remains challenging. In this study, we investigate molecular stereo-electronic effects influencing the kinetic and thermodynamic stability of a .QOOH along its formation path from the precursor, alkylperoxyl radical (ROO.), and the depletion path resulting in the formation of cyclic ether + .OH. We focus on reactive intermediates encountered in the oxidation of acyclic hydrocarbon radicals: ethyl, isopropyl, isobutyl, tert-butyl, neopentyl, and their alicyclic counterparts: cyclohexyl, cyclohexenyl, and cyclohexadienyl. We report reaction energies and barriers calculated with the highly accurate method Weizmann-1 (W1) for the channels: ROO. <=> .QOOH, ROO. <=> alkene + .OOH, .QOOH <=> alkene + .OOH, and .QOOH <=> cyclic ether + .OH. Using W1 results as a reference, we have systematically benchmarked the accuracy of popular density functional theory (DFT), composite thermochemistry methods, and an explicitly correlated coupled-cluster method. We ascertain inductive, resonance, and steric effects on the overall stability of .QOOH and computationally investigate the possibility of forming more stable species. With new reactions as test cases, we probe the capacity of various ab initio methods to yield quantitative insights on the elementary steps of combustion.

physics.chem-ph↗

arXiv2023

Heavy QCD Axion in $b\to s$ transition: Enhanced Limits and Projections

We study a "heavy" QCD axion whose coupling to the standard model is dominated by $a G \widetilde{G}$ but with $m_a \gg m_πf_π/ f_a$. This is well motivated as it can solve the strong CP problem while evading the axion quality problem. It also poses interesting challenges for its experimental search due to its suppressed couplings to photons and leptons. Such axion with mass around a GeV is kinematically inaccessible or poorly constrained by most experimental probes except B-factories. We study $B \to K a$ transitions as a powerful probe of the heavy QCD axion by performing necessary 2-loop calculations for the first time, together with some improvement on the existing analysis strategy. We find some of the existing limits are enhanced by at least an order of magnitude. We also demonstrate that the bounds are robust against unknown UV physics. For forthcoming data sets of the Belle II experiment, we provide a projection that $f_a$ of a few TeV is within its future reach, which is relevant to the quality problem.

hep-ph↗

arXiv2022

Understanding the role of intramolecular ion-pair interactions in conformational stability using an ab initio thermodynamic cycle

Intramolecular ion-pair interactions yield shape and functionality to many molecules. With proper orientation, these interactions overcome steric factors and are responsible for the compact structures of several peptides. In this study, we present a thermodynamic cycle based on isoelectronic and alchemical mutation to estimate intramolecular ion-pair interaction energy. We determine these energies for 26 benchmark molecules with common ion-pair combinations and compare them with results obtained using intramolecular symmetry-adapted perturbation theory. For systems with long linkers, the ion-pair energies evaluated using both approaches deviate by less than 2.5% in vacuum phase. The thermodynamic cycle based on density functional theory facilitates calculations of salt-bridge interactions in model tripeptides with continuum/microsolvation modeling, and four large peptides: 1EJG (crambin), 1BDK (bradykinin), 1L2Y (a mini-protein with a tryptophan cage), and 1SCO (a toxin from the scorpion venom).

physics.chem-ph↗

arXiv2022

Resolution-vs.-Accuracy Dilemma in Machine Learning Modeling of Electronic Excitation Spectra

In this study, we explore the potential of machine learning for modeling molecular electronic spectral intensities as a continuous function in a given wavelength range. Since presently available chemical space datasets provide excitation energies and corresponding oscillator strengths for only a few valence transitions, here, we present a new dataset -- \bigqm -- with 12,880 molecules containing up to 7 CONF atoms and report ground state and excited state properties. A publicly accessible web-based data-mining platform is presented to facilitate on-the-fly screening of several molecular properties including harmonic vibrational and electronic spectra. We present all singlet electronic transitions from the ground state calculated using the time-dependent density functional theory framework with the $ω$B97XD exchange-correlation functional and a diffuse-function augmented basis set. The resulting spectra predominantly span the X-ray to deep-UV region (10--120 nm). To compare the target spectra with predictions based on small basis sets, we bin spectral intensities and show good agreement is obtained only at the expense of the resolution. Compared to this, machine learning models with latest structural representations trained directly using $<10 \%$ of the target data recover the spectra of the remaining molecules with better accuracies at a desirable $<1$ nm wavelength resolution.

physics.chem-ph↗

arXiv2022

Ultra-relativistic bubbles from the simplest Higgs portal and their cosmological consequences

We analyze the phase transitions in the minimal extension of the SM with a real singlet scalar field. The novelty of our study is that we identify and analyze in details the region of parameter space where the first order phase transition can occur and in particular when the bubbles with true vacuum can reach relativistic velocities. This region is interesting since it can lead to the new recently discussed baryogenesis and Dark Matter production mechanisms. We fully analyze different models for the production of Dark Matter and baryogenesis as well as the possibilities of discovery at the current and future experiments.

hep-ph↗

arXiv2022

Displaced Searches for Light Vector Bosons at Belle II

With a design luminosity of 50 ab$^{-1}$ and detectors with tracking capabilities extending beyond 1 m, the Belle II experiment is the perfect laboratory for the search of particles that couple weakly to the Standard Model and have a characteristic decay length of a few centimetres and more. We show that for models of dark photons and other light vector bosons, Belle II will be successful in probing regions of parameter space which are as of now unexplored by any experiment. In addition, for models where the vector boson couples sub-dominantly to the electron and quarks as compared to muons, e.g. in the $L_μ-L_τ$ model, Belle II will probe regions of mass and couplings compatible with the anomalous magnetic moment of muon. We discuss these results and derive the projected sensitivity of Belle II for a handful of other models. Finally, even with the currently accumulated data, $\sim 200$ fb$^{-1}$, Belle II should be able to cover regions of parameter space pertaining to the X(17) boson postulated to solve the ATOMKI anomaly.

hep-ph↗