arXiv subjects

Sudhir K. Vempati

Publications and source records attributed to Sudhir K. Vempati.

At least 19 recordsLinked to original sources

arXiv2026

LFV in flavourful SMEFT: Dimension-Six Running versus Dimension-Eight Mixing

We study how charged-lepton flavour violation (CLFV) generated in the $τ$ sector propagates into the $μ\to e$ sector within the Standard Model Effective Field Theory (SMEFT). Assuming that new physics at a scale $Λ\gg v$ produces only dimension-6 operators that mediate $τ\to e$ and $τ\toμ$ transitions, we identify and compare the three mechanisms that induce $μ\to e$ observables. All three originate from double insertions of the two $τ\to\ell$ operators and scale as $C_6^{τe}C_6^{τμ}/Λ^4$. (T1) Renormalization-group mixing misaligns the charged-lepton mass matrix, and the rotation to the mass basis generates dimension-6 $μ\to e$ operators. (T2) A finite, non-logarithmic remainder, which we find to be negligible. (T3) The overall divergence renormalizes dimension-8 operators, contributing after electroweak symmetry breaking. Since T1 and T3 carry no relative power of $Λ$, neither can be neglected at any scale, and only their comparison reveals which mechanism, and hence which $μ\to e$ observable, most strongly probes a given operator pair. Surveying the Warsaw-basis operators, we classify representative $(τ\to e,τ\toμ)$ pairs into T1-dominated, T3-dominated, and T1--T3-comparable regimes, and explain the hierarchy through the underlying mixing chains. Translating current $μ\to eγ$, $μ\to eee$ and $μ\to e$ conversion limits into bounds on products of $τ\to\ell$ Wilson coefficients, we find that they exceed the direct $τ$-decay constraints by factors of ten to several hundred. Excluding either T1 or T3 would miss these limits by orders of magnitude for some pairs, and shift them by factors of two to three in others. Interpreting $μ\to e$ data as a probe of $τ$ flavour violation therefore requires both the dimension-6 RG running and the dimension-8 mixing contributions.

hep-ph↗

arXiv2026

HEPToolBench 1.2: Testing How Reliably Language Models Can Drive Particle Physics Software

Scientists increasingly want to drive research software by natural-language request, but fluent output helps only if it becomes a correct machine-readable artifact. We introduce HEPToolBench, a benchmark of 28 collider-simulation tasks scored by deterministic, task-specific scorers, plus a three-task structured-debugging extension. We evaluate 42 deployments, from small locally served open-weight models to hosted frontier systems. The central experiment compares direct generation of native HEP-tool syntax with a schema-mediated interface where the model returns a typed representation that deterministic software serializes. Across five matched requests, the mean score rises from 0.418 to 0.902 and task passes from 21/210 to 159/210, with 41 of 42 deployments improving; eleven deployments, seven locally served open-weight models, go from 0/5 passes under native syntax to 5/5 under the structured interface. Values use the corrected v1.2.1 contract, in which the two native scorers that had enforced operational conventions absent from their own prompts are rescored prompt-faithfully cohort-wide. One asymmetry remains: native scorers score the recorded response verbatim and reject Markdown-fenced replies, whereas structured scorers recover JSON from such wrappers; no full-cohort rescoring under a single symmetric extraction rule has been done. An audit of archived responses from 17 locally served deployments shows this does not explain their gains: passes remain six to ten times more frequent under the structured interface when both sides use the same extraction rule. A task pass alone does not guarantee runtime or scientific viability. Within this scope, moving syntax generation into deterministic software can substantially improve reliability for both small local and frontier models. Prompts, scorers, responses, and regeneration scripts are released for independent evaluation and extension.

hep-ph↗

arXiv2026

HEPLocalAgent 1.0: Running Collider Simulations from Plain-Language Requests on Your Own Computer

We present HEPLocalAgent, an open source local interface that builds a bounded class of collider simulation workflows from natural language requests. A locally served language model proposes a typed workflow representation, and deterministic software then restores recognized user stated quantities, builds the HEP tool inputs, validates the supported workflow, and presents the artifacts for approval before execution. In a same response comparison on 47 evaluable model request cases, the first structured proposal gave 7 unmodified artifacts satisfying the external benchmark scorer, against 19 after the full deterministic pipeline. Under the fixed representation normalization defined by the benchmark, the counts were 11 and 43. The direction of improvement is unchanged. The gap between the two views arises because the released builder and the benchmark scorers disagree on three bookkeeping conventions, namely launch form, two fixed control lines, and the output directory name, not on physics content. Four of seven approved workflows ran to completion on the managed local software stack, with cross sections consistent between repeats. In a separate challenge set, 57 of 96 problematic requests still reached the approval stage after part of the request was dropped, defaulted, or reinterpreted. No tested unsafe payload was retained in an executable artifact before the approval gate, but this does not establish operating system level containment. The deterministic backend supports MadGraph, Pythia8, Delphes, and a restricted MadAnalysis 5 plan. Reliable natural language routing to the MadAnalysis stage was not demonstrated in the tested examples. Version 1 should therefore be seen as an inspectable, validation gated workflow constructor requiring expert approval rather than an autonomous or scientifically self validating agent.

hep-ph↗

arXiv2026

Discovery prospects of a singly-charged scalar at $μ$TRISTAN

In this article, we study the associated production of a singly-charged ($Δ^+$) scalar along with a $W^+$ boson in the newly proposed $μ^+μ^+$ collider (also known as $μ$TRISTAN) at $\sqrt{s} = 2~$ TeV. Such a singly-charged scalar is naturally accommodated in an extremely well-motivated neutrino mass model, namely, the Type-II seesaw model. This model, beside providing a viable explanation of neutrino mass generation, also allows for lepton flavor violating (LFV) processes. Since LFV processes are not allowed in the Standard Model (SM), we focus on the discovery prospect of the singly-charged scalar in the Type-II seesaw model at $μ$TRISTAN through a LFV process, owing to the advantage of this process being free of any SM background. Additionally, this article also proposes a method to indicate if the underlying theory follows a Normal or an Inverted hierarchy depending on the distribution of lepton flavors in the final state.

hep-ph↗

arXiv2026

Theoretical and Experimental Constraints in the $μ$--$τ$ Four-Lepton Sector of the SMEFT: implications to neutrino self interactions

We study the dimension-six SMEFT four-lepton operators in the $μ$--$τ$ sector. These operators control both charged-lepton scattering and neutrino self-interactions, the latter being weakly constrained by direct laboratory probes despite their importance for cosmological tensions. We compare three classes of constraints on the Warsaw-basis coefficients $[C_{\ell\ell}]_{2222}$, $[C_{\ell\ell}]_{2233}$, and $[C_{\ell\ell}]_{2332}$. We use perturbative unitarity from $2\!\to\!2$ partial-wave analysis, spin-summing positivity sum rules, and the experimental bounds from NA64$μ$ and the global fit~\cite{Falkowski:2017pss}. We find that the global fit dominates for $[C_{\ell\ell}]_{2222}$ and $[C_{\ell\ell}]_{2332}$, while NA64$μ$ provides the leading bound on $[C_{\ell\ell}]_{2233}$, with the unitarity line for this direction entering the range of collider energies near $200~\mathrm{GeV}$. Renormalization-group running between $1~\mathrm{GeV}$ and $30~\mathrm{TeV}$ modifies these coefficients by up to $10\%$. Translating these bounds onto the effective four-neutrino coupling $G_\mathrm{eff}$, we find values many orders of magnitude smaller than the strongly interacting regime motivated by the Hubble tension; this excludes heavy-mediator UV completions of strong $ν_μ$--$ν_μ$ and $ν_μ$--$ν_τ$ self-interactions within the validity of the dimension-six SMEFT and in the absence of tuned cancellations between operators, while leaving the cosmologically motivated light-mediator scenarios unconstrained by this analysis. Finally, we comment on the bounds these coefficients place on a leptophilic $L_μ- L_τ$ $Z'$ UV completion. Our SMEFT-based current and projected NA64$μ$ bounds reproduce the dedicated $Z'$ analyses already available in the literature.

hep-ph↗

arXiv2024

Aspects of Non-local QED and the Weak Gravity Conjecture

We use the Weak Gravity Conjecture (WGC) to investigate the impact of charge dequantization arising from non-local QED on the scale of non-locality of neutrinos. We find this scale to be <= 87 TeV, which could be probed in future colliders. We also investigate the electric force and potential in non-local QED and use them to reformulate the Weak Gravity Conjecture (WGC) in non-local QED.

hep-ph↗

arXiv2024

Flavor Violating Di- Higgs Coupling

Di-Higgs couplings to fermions of the form $h^{2}\overline{f}f$ are absent in the Standard Model, however, they are present in several physics Beyond Standard Model (BSM) extensions, including those with vector-like fermions. In Effective Field Theories (EFTs), such as the Standard Model Effective Field Theory (SMEFT) and the Higgs Effective Field Theory (HEFT), these couplings appear at dimension 6 and can in general, be flavour-violating (FV). In the present work, we employ a bottom-up approach to investigate the FV in the lepton and quarks sectors through the di-Higgs effective couplings. We assume that all FV arises from this type of couplings and assume that the Yukawa couplings $Y_{ij}$ are given by their SM values, i.e. $Y_{ij} = \sqrt{2}m_{i}δ_{ij}/v$. In the lepton sector, we set upper limits on the Wilson coefficients $C_{ll'}$ from $l \rightarrow 3l'$ decays, $l \rightarrow lγ$ decays, muonium oscillations, the $(g-2)_μ$ anomaly, LEP searches, muon conversion in nuclei, FV Higgs decays, and $Z$ decays. We also make projections on some of these coefficients from Belle II, the Mu2e experiment and the LHC's High Luminosity (HL) run. In the quark sector, we set upper limits on the Wilson coefficients $C_{qq'}$ from meson oscillations and from $B$-physics searches. A key takeaway from this study is that current and future experiments should set out to measure the effective di-Higgs couplings $C_{ff'}$, whether these couplings are FV or flavour-conserving. We also present a matching between our formalism and the SMEFT operators and show the bounds in both bases.

hep-ph↗

arXiv2024

The Generalized Scalar Weak Gravity Conjecture and its Implications

We propose a generalized formulation of the Scalar Weak Gravity Conjecture (SWGC) based on the analogy with the derivation of the Gauge Weak Gravity Conjecture (GWGC). We discuss some phenomenological implications of this Generalized SWGC, including the scale of New Physics (NP) when applied to the SM Higgs sector, and the bounds on the axion's couplings to fermions and the photon when applied to the axion. The Generalized SWGC constraints rule out most of the parameter space of axion-nucleon couplings, leaving only a tiny parameter space.

hep-ph↗

arXiv2024

Corrected Calculation for the Non-local Solution to the g-2 Anomaly and Novel Results in Non-local QED

We provide the corrected calculation of the muon g-2 in non-local QED previously done in the literature. In specific, we show the proper technique for calculating loops in non-local QED and use it to find the form factors F1(q1) and F2(q2) in non-local QED. We also utilize this technique to calculate some novel results in non-local QED, including calculating the correction to the photon self-energy, the modification to the classical Coulomb potential, the modification to the energy levels of the hydrogen atom, and the contribution to the Lamb shift. We also discuss charge dequantization through non-locality, and show that the experimental bounds on the electric charge on Dirac neutrinos, translate into strong flavor-dependent bounds on the scale on non-locality that range between 10^5 - 10^10 TeV. We also discuss the inconsistencies of unrenormalized non-local Quantum Field Theories (QFTs) and the need for renormalizing them, even when they are free from UV divergences.

hep-ph↗

arXiv2023

Can the Higgs Still Account for the g-2 Anomaly?

We use an Effective Field Theory (EFT) approach to evaluate the viability of the Higgs to account for the $g-2$ anomaly. Although the SM contribution of the Higgs to the muon's magnetic dipole moment is negligible, using a \textit{bottom-up} EFT, we show that given the current level of experimental limits on the Higgs sector, the Higgs can still yield a viable solution to the $g-2$ anomaly if its couplings to the rest of the SM particles are allowed to deviate from their SM predictions. Further, applying unitarity arguments, we show that such a solution would indicate a scale of New Physics (NP) of $\sim 10 -18$ TeV, which could be lowered to $\sim 5$ TeV if the Higgs couplings to the $W$ and $Z$ are assumed to conform to their SM predictions. We show that such a scenario could yield significant enhancement to the di-Higgs production in muon colliders, thus providing further motivation for its consideration. A key takeaway of this study is to highlight the importance of measuring the $\barμ μhh$ coupling in future experiments.

hep-ph↗

arXiv2023

Faint light of old neutron stars and detectability at the James Webb Space Telescope

Isolated ideal neutron stars (NS) of age $>10^9$ yrs exhaust thermal and rotational energies and cool down to temperatures below $\mathcal{O}(100)$ K. Accretion of particle dark matter (DM) by such NS can heat them up through kinetic and annihilation processes. This increases the NS surface temperature to a maximum of $\sim 2550$ K in the best case scenario. The maximum accretion rate depends on the DM ambient density and velocity dispersion, and on the NS equation of state and their velocity distributions. Upon scanning over these variables, we find that the effective surface temperature varies at most by $\sim 40\%$. Black body spectrum of such warm NS peak at near infrared wavelengths with magnitudes in the range potentially detectable by the James Webb Space Telescope (JWST). Using the JWST exposure time calculator, we demonstrate that NS with surface temperatures $\gtrsim 2400$ K, located at a distance of 10\,pc can be detected through the F150W2 (F322W2) filters of the NIRCAM instrument at SNR\,$\gtrsim 10$ (5) within 24 hours of exposure time. Independently of DM, an observation of NS with surface temperatures $\gtrsim 2500$ K will be a formative step towards testing the minimal cooling paradigm during late evolutionary stages.

astro-ph.HE↗

arXiv2023

Supersymmetry : A decade after Higgs discovery

Supersymmetric extensions of the Standard Model have been in vogue for over half a century. They have many interesting theoretical properties like calculability, absence of quadratic divergences, and phenomenologically impactful features like gauge coupling unification, dark matter candidates, signatures at present and future colliders, etc. A defining feature of these models is the calculability of Higgs mass in terms of a few parameters. The discovery of a Higgs particle with a mass of around 125 GeV thus has significant implications. The null results for the searches of superpartners at LHC has also put further constraints. Taken together with direct detection limits on WIMP (Weakly Interacting Massive Particle) dark matter, it appears that TeV scale supersymmetry is not realised in Nature and the theoretical expectations have reached a turning point. The present onslaught from the experiments suggests that supersymmetric models need a more complex particle structure, lagrangian and breaking patterns to be a natural solution to the hierarchy problem. We review existing models and discuss their feasibility in the current and future experimental programs.

hep-ph↗

arXiv2023

A Proposed Renormalization Scheme for Non-local QFTs and Application to the Hierarchy Problem

We propose a renormalization scheme for non-local Quantum Field Theories (QFTs) with infinite derivatives inspired by string theory. Our Non-locality Renormalization Scheme (NRS) is inspired by Dimensional Regularization (DR) in local QFTs and is shown to significantly improve the UV behavior of non-local QFTs. We illustrate the scheme using simple examples from the phi3 and phi4 theories, then we evaluate the viability of NRS-enhanced non-local QFTs to solve the hierarchy problem using a simplified toy model. We find that non-locality protects the mass of a light scalar from receiving large corrections from any UV sector to which it couples, as long as the non-locality scale M is sufficiently smaller than the scale of the UV sector. We also find that NRS eliminates any large threshold corrections from the IR sector

hep-th↗

arXiv2022

Restricting $q^2 l^2$ operators from $π^0 \rightarrow μe$

In this paper we consider semileptonic lepton flavor violating operators of the type $q^2l^2$ in low energy effective theory (LEFT). At the chiral scale, we match these operators to chiral perturbation theory ($χ$PT) and place constraints from the process $π^0\rightarrow μ^+ \,\, e^-$. These bounds are shown to depend on the chiral nature of the operators. The scalar operators are significantly more constrained compared to the vector operators. We then compare the limits from $μ\to e$ conversion in Nuclei and show that the limits on scalar operators are within an order of magnitude of the corresponding limits from $μ\to e$ conversion in Ti. On the other hand, the limits on vector operators are however much weaker. Towards the end, we evolve the LEFT operators to W-boson mass scale using RGE, and match them to the Standard Model effective field theory (SMEFT) operators. We, then, derive the constraints on the parameter space of Leptoquark models that could generate these SMEFT operators at tree level.

hep-ph↗

arXiv2021

Freezing In with Lepton Flavored Fermions

Dark, chiral fermions carrying lepton flavor quantum numbers are natural candidates for freeze-in. Small couplings with the Standard Model fermions of the order of lepton Yukawas are `automatic' in the limit of Minimal Flavor Violation. In the absence of total lepton number violating interactions, particles with certain representations under the flavor group remain absolutely stable. For masses in the GeV-TeV range, the simplest model with three flavors, leads to signals at future direct detection experiments like DARWIN. Interestingly, freeze-in with a smaller flavor group such as $SU(2)$ is already being probed by XENON1T.

hep-ph↗

arXiv2021

Taming the $ε_K$ in Little Randall Sundrum Models

The Randall Sundrum (RS) models receive significant constraints from the neutral Kaon system. The CP violating observable $ε_K$, in Randall Sundrum scenario, requires the lightest KK gluon to be heavier than $\sim$ 24 TeV. The constraint is even stronger in the Little Randall Sundrum models (LRS), $\gtrsim$ 32 TeV. The LRS models are motivated for their possible visibility at the Large Hardon Collider (LHC). We show that the stringent constraints from K-physics can be relaxed in the LRS models, in the presence of the Brane Localised Kinetic Terms (BLKT). In particular, for a range of values, a UV BLKT could significantly modify the lightest KK gluon wave function such that the limit can reduces to 5 TeV. We also show that such a relaxation of the constraints can also be achieved by imposing flavour symmetries {à la } Minimal Flavour Protection.

hep-ph↗

arXiv2019

Diluting SUSY flavour problem on the Landscape

We consider an explicit effective field theory example based on the Bousso-Polchinski framework with a large number N of hidden sectors contributing to supersymmetry breaking. Each contribution comes from four form quantized fluxes, multiplied by random couplings. The soft terms in the observable sector in this case become random variables, with mean values and standard deviations which are computable. We show that this setup naturally leads to a solution of the flavor problem in low-energy supersymmetry if N is sufficiently large. We investigate the consequences for flavor violating processes at low-energy and for dark matter.

hep-ph↗

arXiv2017

Clockwork for Neutrino Masses and Lepton Flavor Violation

We investigate the generation of small neutrino masses in a clockwork framework which includes Dirac mass terms as well as Majorana mass terms for the new fermions. We derive analytic formulas for the masses of the new particles and for their Yukawa couplings to the lepton doublets, in the scenario where the clockwork parameters are universal. When the Majorana masses all vanish, the zero mode of the clockwork sector forms a Dirac pair with the active neutrino, with a mass which is in agreement with oscillations experiments for a sufficiently large number of clockwork gears. On the other hand, when the Majorana masses do not vanish, neutrino masses are generated via the seesaw mechanism. In this case, and due to the fact that the effective Yukawa couplings of the higher modes can be sizable, neutrino masses can only be suppressed by postulating a large Majorana mass for all the gears. Finally, we discuss the constraints on the mass scale of the clockwork fermions from the non-observation of the rare leptonic decay $μ\rightarrow eγ$.

hep-ph↗