arXiv subjects

Sumit K. Garg

Publications and source records attributed to Sumit K. Garg.

At least 19 recordsLinked to original sources

arXiv2026

The Alternative Left-Right Scenario: Unitarity, Vacuum Stability and RG Evolution

We study the theoretical constraints on the scalar sector of the Alternative Left-Right Model (ALRM), an $E_6$-motivated extension of the Standard Model based on the gauge group $\mathrm{SU}(3)_c \otimes \mathrm{SU}(2)_L \otimes \mathrm{SU}(2)_{R'} \otimes \mathrm{U}(1)_{B-L}$, supplemented by a global $\mathrm{U}(1)_S$ symmetry. We derive the complete set of tree-level perturbative unitarity constraints on the model, resulting in 14 independent conditions on the quartic scalar couplings. When combined with the boundedness-from-below conditions and the requirement of positive-definite scalar mass-squared eigenvalues, these constraints are found to be complementary, with their simultaneous imposition yielding significantly more stringent restrictions on the parameter space than either set alone. We then perform a one loop renormalization group analysis, evolving the model parameters from the electroweak scale up to a high energy cut-off scale, and requiring that the vacuum stability, the unitarity, and the perturbativity conditions are preserved throughout. The renormalisation group evolution is found to restrict the allowed parameter space considerably beyond the tree-level bounds, with the constraints on the quartic couplings becoming more stringent as the cut off scale is raised. Consequently, the physical scalar masses in the model acquire upper bounds. For the right-hand symmetry breaking scale, $v_R = 10$ TeV and requiring theoretical consistency up to $10^{16}$ GeV, we obtain $m_{H_1^\pm} \lesssim 6.5$ TeV, $m_{H_2^\pm} \lesssim 1.5$ TeV, and $m_{H_1^0} \simeq m_{A_1} \lesssim 1.3$ TeV, with all bounds scaling with $v_R$. These findings offer a predictive and falsifiable framework for searches of the extended Higgs sector of the ALRM at the current and future collider experiments.

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arXiv2025

Deep learning approaches to top FCNC couplings to photons at the LHC

We investigate the sensitivity of the LHC to flavour-changing neutral current interactions involving the top quark and a photon using a model-independent effective field theory framework, focusing on two complementary processes: single top production via $qg \to t\gamma$ and the rare decay $t \to q\gamma$ in top pair events. To enhance signal discrimination, we employ a range of deep learning classifiers, including multi-layer perceptrons, graph attention networks and transformers, and compare them against a traditional cut-based analysis. Our results demonstrate that attention-based architectures, in particular transformer networks, significantly outperform other strategies, yielding up to a factor of five improvement in the expected exclusion limits. In particular, we show that at the high-luminosity LHC, rare top branching ratios can be probed down to values as low as $10^{-6}$. Our results thus highlight the significant potential of attention-based architectures for improving the sensitivity to new physics signatures in top quark processes at colliders.

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arXiv2024

Leptonic probes of Alternative Left-Right Symmetric Models

We explore constraints on the parameter space of the alternative left-right model originating from the leptonic sector. Our analyses focuses on both lepton-flavour-conserving observables, particularly the anomalous magnetic moment of the muon, and lepton-flavour-violating processes like $\mu \to e \gamma $ decay and $\mu-e$ conversions in nuclei. While contributions to the anomalous magnetic moment fall below the measured values at 2$\sigma$, current and future experimental sensitivities to flavour-violating branching rations of the Standard Model leptons are expected to impose lower bounds on the mass of the peculiar $SU(2)_R$ gauge boson of the model. This provides complementary constraints relative to existing limits, which are indirect and derived from collider bounds on the mass of the associated neutral gauge boson $Z^\prime$.

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arXiv2024

Flavour-changing top quark decays in the alternative left-right model

We examine flavour-changing neutral-current decays of the top quark, $t\to q γ$, $t \to qZ$, $t \to q H$, and $ t\to q g$ (with $q=u, c$), in the Alternative Left-Right Model, a left right-symmetric model featuring exotic quarks and light bosons. These decays have a very small probability of occurring within the Standard Model, but they can be enhanced in this model through the presence of the exotic states. While associated signals may be detected directly at the LHC, rare decays have the advantage of offering means to probe new particles indirectly, through loop-contributions. We perform a comprehensive analysis of the model's parameter space to demonstrate the possible existence of enhancements in the corresponding branching ratios, of $10^6$ for the branching ratios $\mathcal{B}(t\to uZ)$ and $\mathcal{B}(t \to uH)$, and in the range of $10^{2} - 10^{4}$ for the other decays, relative to the Standard Model. We subsequently determine the preferred parameter space regions of the model in terms of potential of being reached in the near future.

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arXiv2024

What is the Simplest Linear Ramp?

We discuss conditions under which a deterministic sequence of real numbers, interpreted as the set of eigenvalues of a Hamiltonian, can exhibit features usually associated to random matrix spectra. A key diagnostic is the spectral form factor (SFF) -- a linear ramp in the SFF is often viewed as a signature of random matrix behavior. Based on various explicit examples, we observe conditions for linear and power law ramps to arise in deterministic spectra. We note that a very simple spectrum with a linear ramp is $E_n \sim \log n$. Despite the presence of ramps, these sequences do $not$ exhibit conventional level repulsion, demonstrating that the lore about their concurrence needs refinement. However, when a small noise correction is added to the spectrum, they lead to clear level repulsion as well as the (linear) ramp. We note some remarkable features of logarithmic spectra, apart from their linear ramps: they are closely related to normal modes of black hole stretched horizons, and their partition function with argument $s=β+it$ is the Riemann zeta function $ζ(s)$. An immediate consequence is that the spectral form factor is simply $\sim |ζ(it)|^2$. Our observation that log spectra have a linear ramp, is closely related to the Lindelöf hypothesis on the growth of the zeta function. With elementary numerics, we check that the slope of a best fit line through $|ζ(it)|^2$ on a log-log plot is indeed $1$, to the fourth decimal. We also note that truncating the Riemann zeta function sum at a finite integer $N$ causes the would-be-eternal ramp to end on a plateau.

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arXiv2023

Fuzzballs and Random Matrices

Black holes are believed to have the fast scrambling properties of random matrices. If the fuzzball proposal is to be a viable model for quantum black holes, it should reproduce this expectation. This is considered challenging, because it is natural for the modes on a fuzzball microstate to follow Poisson statistics. In a previous paper, we noted a potential loophole here, thanks to the modes depending not just on the $n$-quantum number, but also on the $J$-quantum numbers of the compact dimensions. For a free scalar field $ϕ$, by imposing a Dirichlet boundary condition $ϕ=0$ at the stretched horizon, we showed that this $J$-dependence leads to a linear ramp in the Spectral Form Factor (SFF). Despite this, the status of level repulsion remained mysterious. In this letter, motivated by the profile functions of BPS fuzzballs, we consider a generic profile $ϕ= ϕ_0(θ)$ instead of $ϕ=0$ at the stretched horizon. For various notions of genericity (eg. when the Fourier coefficients of $ϕ_0(θ)$ are suitably Gaussian distributed), we find that the $J$-dependence of the spectrum exhibits striking evidence of level repulsion, along with the linear ramp. We also find that varying the profile leads to natural interpolations between Poisson and Wigner-Dyson(WD)-like spectra. The linear ramp in our previous work can be understood as arising via an extreme version of level repulsion in such a limiting spectrum. We also explain how the stretched horizon/fuzzball is different in these aspects from simply putting a cut-off in flat space or AdS (ie., without a horizon).

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arXiv2019

Model independent Analysis of Dirac CP Violating Phase for some well known mixing scenarios

We present a model-independent analysis of Leptonic CP violation for some well known mixing scenarios. In particular, we considered modified schemes for Bimaximal(BM), Democratic(DC), Hexagonal(HG) and Tribimaixmal(TBM) mixing for our numerical investigation. These model-independent corrections to mixing matrices are parameterized in terms of complex rotation matrices ($U$) with related modified PMNS matrix of the forms \big($U_{ij}^l\cdot V_{M},~V_{M}\cdot U_{ij}^r$ \big ) where $U_{ij}^{l, r}$ is complex rotation in ij sector and $V_{M}$ is unperturbed mixing scheme. We present generic formulae for mixing angles, Dirac CP phase($δ_{CP}$) and Jarkslog Invariant($J_{CP}$) in terms of correction parameters. The parameter space of each modified mixing case is scanned for fitting neutrino mixing angles using $χ^2$ approach and the corresponding predictions for Leptonic CP Phase($δ_{CP}$) and Jarkslog Invariant($J_{CP}$) has been evaluated from allowed parameter space. The obtained ranges are reported for all viable cases.

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arXiv2019

Bounds on Slow Roll at the Boundary of the Landscape

We present strong evidence that the tree level slow roll bounds of arXiv:1807.05193 and arXiv:1810.05506 are valid, even when the tachyon has overlap with the volume of the cycle wrapped by the orientifold. This extends our previous results in the volume-dilaton subspace to a semi-universal modulus. Emboldened by this and other observations, we investigate what it means to have a bound on (generalized) slow roll in a multi-field landscape. We argue that for $any$ point $ϕ_0$ in an $N$-dimensional field space with $V(ϕ_0) > 0$, there exists a path of monotonically decreasing potential energy to a point $ϕ_1$ within a path length $\lesssim {\cal O}(1)$, such that $\sqrt{N}\ln \frac{V(ϕ_1)}{V(ϕ_0)} \lesssim - {\cal O} (1)$. The previous de Sitter swampland bounds are specific ways to realize this stringent non-local constraint on field space, but we show that it also incorporates (for example) the scenario where both slow roll parameters are intermediate-valued and the Universe undergoes a small number of e-folds, as in the Type IIA set up of arXiv:1310.8300. Our observations are in the context of tree level constructions, so we take the conservative viewpoint that it is a characterization of the classical "boundary" of the string landscape. To emphasize this, we argue that these bounds can be viewed as a type of Dine-Seiberg statement.

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arXiv2019

A Systematic Analysis of Perturbations for Hexagonal Mixing Matrix

We present a systematic analysis of perturbative Hexagonal(HG) mixing for describing recent global fit neutrino mixing data with normal and inverted hierarchy. The corrections to unperturbed mixing are parameterized in terms of small orthogonal rotations (R) with modified PMNS matrix of the forms \big($R_{αβ}^l\cdot V_{HG},~V_{HG}\cdot R_{αβ}^r,~V_{HG}\cdot R_{αβ}^r \cdot R_{γδ}^r,~R_{αβ}^l \cdot R_{γδ}^l \cdot V_{HG}$,~$R_{αβ}^l\cdot V_{HG}\cdot R_{γδ}^r$\big ). Here $R_{αβ}^{l, r}$ is rotation in ij sector and $V_{HG}$ is unperturbed Hexagonal mixing matrix. The detailed numerical investigation of all possible cases is performed with scanning of parameter space using $χ^2$ approach. We found that the perturbative schemes governed by single rotation are unable to fit the mixing angle data even at $3σ$ level. The mixing schemes which involves two rotation matrices, only \big($R_{12}^l \cdot R_{13}^l \cdot V_{HG}$, ~$R_{13}^l \cdot R_{12}^l \cdot V_{HG}$,~$R_{13}^l \cdot V_{HG} \cdot R_{12}^r$,~$R_{12}^l \cdot V_{HG} \cdot R_{12}^r$, ~$R_{13}^l \cdot V_{HG} \cdot R_{13}^r$\big ) are successful in fitting all neutrino mixing angles within $1σ$ range for normal hierarchy(NH). However for inverted hierarchy(IH), only $R_{13}^l \cdot V_{HG} \cdot R_{13}^r$ is most preferable as it can fit all mixing angles at $1σ$ level. The remaining perturbative cases are either excluded at 3$σ$ level or successful in producing mixing angles only at $2-3σ$ level. To study the impact of phase parameter, we also looked into CP violating effects for single rotation case. The predicted value of $δ_{CP}$ lies in the range $39.0^\circ(40.4^\circ) \le |δ_{CP}| \le 78.7^\circ(79.2^\circ)$ for $U_{12}^l\cdot V_{HM}$ and $U_{13}^l\cdot V_{HM}$ case with Normal(Inverted) Hierarchy.

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arXiv2018

Bounds on Slow Roll and the de Sitter Swampland

The recently introduced swampland criterion for de Sitter (arXiv:1806.08362) can be viewed as a (hierarchically large) bound on the smallness of the slow roll parameter $ε_V$. This leads us to consider the other slow roll parameter $η_V$ more closely, and we are lead to conjecture that the bound is not necessarily on $ε_V$, but on slow roll itself. A natural refinement of the de Sitter swampland conjecture is therefore that slow roll is violated at ${\cal O}(1)$ in Planck units in any UV complete theory. A corollary is that $ε_V$ need not necessarily be ${\cal O}(1)$, if $η_V \lesssim -{\cal O}(1)$ holds. We consider various tachyonic tree level constructions of de Sitter in IIA/IIB string theory (as well as closely related models of inflation), which superficially violate arXiv:1806.08362, and show that they are consistent with this refined version of the bound. The phrasing in terms of slow roll makes it plausible why both versions of the conjecture run into trouble when the number of e-folds during inflation is high. We speculate that one way to evade the bound could be to have a large number of fields, like in $N$-flation.

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arXiv2018

Consistency of perturbed Tribimaximal, Bimaximal and Democratic mixing with Neutrino mixing data

We scrutinize corrections to tribimaximal (TBM), bimaximal (BM) and democratic (DC) mixing matrices for explaining recent global fit neutrino mixing data. These corrections are parameterized in terms of small orthogonal rotations (R) with corresponding modified PMNS matrices of the forms \big($R_{ij}^l\cdot U,~U\cdot R_{ij}^r,~U \cdot R_{ij}^r \cdot R_{kl}^r,~R_{ij}^l \cdot R_{kl}^l \cdot U$\big ) where $R_{ij}^{l, r}$ is rotation in ij sector and U is any one of these special matrices. We showed that for perturbative schemes dictated by single rotation, only \big($ R_{12}^l\cdot U_{BM},~R_{13}^l\cdot U_{BM},~U_{TBM}\cdot R_{13}^r$ \big ) can fit the mixing data at $3σ$ level. However for $R_{ij}^l\cdot R_{kl}^l\cdot U$ type rotations, only \big ($R_{23}^l\cdot R_{13}^l \cdot U_{DC} $\big ) is successful to fit all neutrino mixing angles within $1σ$ range. For $U\cdot R_{ij}^r\cdot R_{kl}^r$ perturbative scheme, only \big($U_{BM} \cdot R_{12}^r\cdot R_{13}^r$,~$U_{DC} \cdot R_{12}^r\cdot R_{23}^r$,~$U_{TBM} \cdot R_{12}^r\cdot R_{13}^r$\big ) are consistent at $1σ$ level. The remaining double rotation cases are either excluded at 3$σ$ level or successful in producing mixing angles only at $2σ-3σ$ level. We also updated our previous analysis on PMNS matrices of the form \big($R_{ij}\cdot U \cdot R_{kl}$\big ) with recent mixing data. We showed that the results modifies substantially with fitting accuracy level decreases for all of the permitted cases except \big($R_{12}\cdot U_{BM}\cdot R_{13}$, $R_{23}\cdot U_{TBM}\cdot R_{13}$ and $R_{13}\cdot U_{TBM} \cdot R_{13}$\big ) in this rotation scheme.

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arXiv2014

Top Yukawa coupling measurement with indefinite CP Higgs in $e^+e^-\to t\bar{t}Φ$

We consider the issue of the top quark Yukawa coupling measurement in a model in dependent and general case with the inclusion of CP-violation in the coupling. Arguably the best process to study this coupling is the associa ted production of Higgs boson along with a $t\bar t$ pair in a machine like the International Linear Collider (ILC). While detailed analyses of the sensitivity of the measurement assuming a Standard Model (SM) - like coupling are available in the context of ILC, conclude that th e coupling could be pinned down at about 10\% level with modest luminosity, our investigations show that the scenario could be different in case of a more general coupling. The modified Lorentz structure resulting in a changed functional dependence of the cross section on the couplin g, along with the difference in the cross section itself leads to considerable deviation in the sensitivity. Our studies with an ILC of center of mass energies of 500 GeV, 800 GeV and 1000 GeV show that moderate CP-mixing in the Higgs sector could change the sensitivity to about 20\ %, while it could be worsened to 75\% in cases which could accommodate more dramatic changes in the coupling. While detailed considerations of the decay distributions point to a need for a relook at the analysis strategy followed for the case of SM such as for a model independent analysis of the top quark Yukawa coupling measurement. This study strongly suggests that, a joint analysis of the CP properties and the Yukawa coupling measurement would be the way forward at the ILC and that caution must be excercised in the measurem ent of the Yukawa couplings and the conclusions drawn from it.

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arXiv2013

Corrections for tribimaximal, bimaximal and democratic neutrino mixing matrices

In this work we analyze the corrections to tribimaximal (TBM), bimaximal (BM) and democratic (DC) mixing matrices for explaining large reactor mixing angle $θ_{13}$ and checking the consistency with other neutrino mixing angles. The corrections are parameterized in terms of small orthogonal rotations (R) with corresponding modified PMNS matrix of the form $R_{ij}\cdot U \cdot R_{kl}$ where $R_{ij}$ is rotation in ij sector and U is any one of these special matrices. We showed the rotations $R_{13}\cdot U \cdot R_{23}$, $R_{12}\cdot U \cdot R_{13}$ for BM and $R_{13}\cdot U \cdot R_{13}$ for TBM perturbative case successfully fit all neutrino mixing angles within $1σ$ range. The perturbed PMNS matrix $R_{12}\cdot U \cdot R_{13}$ for DC, TBM and $R_{23}\cdot U \cdot R_{23}$ for TBM case is successful in producing mixing angles at 2$σ$ level. The other rotation schemes are either excluded or successful in producing mixing angles at $3σ$ level.

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arXiv2013

Vector like leptons with extended Higgs sector

We examined the influence of additional scalar doublet on the parameter space of the Standard Model supplemented with a generation of new vector like leptons. In particular we identified the viable regions of parameter space by inspecting various constraints especially electroweak precision (S, T and U) parameters. We demonstrated that the additional scalar assists in alleviating the tension of electroweak precision constraints and thus permitting larger Yukawa mixing and mass splittings among vector like species. We also compared and contrasted the regions of parameter space pertaining to the latest LHC Higgs to diphoton channel results in this scenario with vector like leptons in single Higgs doublet and pure two Higgs doublet model case.

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arXiv2013

Probing the indefinite CP nature of the Higgs Boson through decay distributions in the process $e^+e^-\to t\bar{t}Φ$

The recently discovered scalar resonance at the LHC is now almost confirmed to be a Higgs Boson, whose CP properties are yet to be established. At the ILC with and without polarized beams, it may be possible to probe these properties at high precision. In this work, we study the possibility of probing departures from the pure CP-even case, by using the decay distributions in the process $e^+ e^- \to t \bar{t} Φ$, with $Φ$ mainly decaying into a $b\bar b$ pair. We have compared the case of a minimal extension of the SM case (Model I) with an additional pseudoscalar degree of freedom, with a more realistic case namely the CP-violating Two-Higgs Doublet Model (Model II) that permits a more general description of the couplings. We have considered the ILC with $\sqrt{s}=800$\,GeV and integrated luminosity of $300\, {\rm fb}^{-1}$. Our main findings are that even in the case of small departures from the CP-even case, the decay distributions are sensitive to the presence of a CP-odd component in Model II, while it is difficult to probe these departures in Model I unless the pseudoscalar component is very large. Noting that the proposed degrees of beam polarization increases the statistics, the process demonstrates the effective role of beam polarization in studies beyond the Standard Model. Further, our study shows that an indefinite CP Higgs would be a sensitive laboratory to physics beyond the SM.

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arXiv2012

Anomalous Triple Gauge Boson Couplings in $e^{-}e^{+} \to γγ$ for Non Commutative Standard Model

We investigate $e^{+}e^{-}\to γγ$ process within the Seiberg-Witten expanded noncommutative standard model(NCSM) scenario in the presence of anomalous triple gauge boson couplings. This study is done with and without initial beam polarization and we restrict ourselves to leading order effects of non commutativity i.e. $O(Θ)$. The non commutative(NC) corrections are sensitive to the electric component($\vecΘ_E$) of NC parameter. We include the effects of earth rotation in our analysis. This study is done by investigating the effects of non commutativity on different time averaged cross section observables. We have also defined forward backward asymmetries which will be exclusively sensitive to anomalous couplings. We have looked into the sensitivity of these couplings at future experiments at the International Linear Collider(ILC). This analysis is done under realistic ILC conditions with the Center of mass energy(c.m.) $\sqrt{s}=800$GeV and integrated luminosity L=500fb${}^{-1}$. The scale of non commutativity is assumed to be $Λ= 1$TeV. The limits on anomalous couplings of the order $10^{-1}$ from forward backward asymmetries while much stringent limits of the order $10^{-2}$ from total cross section are obtained if no signal beyond SM is seen.

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arXiv2012

Isolating CP-violating γZZ coupling in e+e- \to γZ with transverse beam polarizations

We revisit the process $e^+e^- \to γZ$ at the ILC with transverse beam polarization in the presence of anomalous CP-violating $γZ Z$ coupling $λ_1$ and $γγZ$ coupling $λ_2$. We point out that if the final-state spins are resolved, then it becomes possible to fingerprint the anomalous coupling {\rm Re}$λ_1$.90% confidence level limit on {\rm Re}$λ_1$ achievable at ILC with center-of-mass energy of 500 GeV or 800 GeV with realistic initial beam polarization and integrated luminosity is of the order of few times of $10^{-2}$ when the helicity of $Z$ is used and $10^{-3}$ when the helicity of $γ$ is used. The resulting corrections at quadratic order to the cross section and its influence on these limits are also evaluated and are shown to be small. The benefits of such polarization programmes at the ILC are compared and contrasted for the process at hand. We also discuss possible methods by which one can isolate events with a definite helicity for one of the final-state particles.

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arXiv2012

The New Minimal Supersymmetric GUT : Spectra, RG analysis and Fermion Fits

The supersymmetric SO(10) GUT based on the ${\bf{210\oplus 10\oplus 120\oplus 126\oplus {\bar {126}}}}$ Higgs system provides a minimal framework for the emergence of the R-parity exact MSSM at low energies and a viable supersymmetric seesaw explanation for the observed neutrino masses and mixing angles. We present formulae for MSSM decomposition of the superpotential invariants, tree level light charged fermion effective Yukawa couplings, Weinberg neutrino mass generation operator, and the $d=5,ΔB=ΔL \neq 0$ effective superpotential in terms of GUT parameters. We use them to determine fits of the 18 available fermion mass-mixing data in terms of the superpotential parameters of the NMSGUT and SUGRY(NUHM) type soft supersymmetry breaking parameters ($\{m_{\tilde f},m_{1/2},A_0,M^2_{H,\bar H}\} $) specified at the MSSM one loop unification scale $M_X^0=10^{16.33} $ GeV. Our fits are compatible with electroweak symmetry breaking and Unification constraints and yield right-handed neutrino masses in the leptogenesis relevant range : $10^8-10^{13} $ GeV. Matching the SM data requires lowering the strange and down quark Yukawas in the MSSM via large $\tanβ$ driven threshold corrections and characteristic soft Susy breaking spectra. The Susy spectra have light pure Bino LSP, heavy exotic Higgs(inos) and large $ μ,A_0,M_{H,\bar{H}}$ parameters $\sim 100$ TeV. Typically third generation sfermions are much \emph{heavier} than the first two generations. The smuon is often the lightest charged sfermion thus offering a Bino-CDM co-annihilation channel. The parameter sets obtained are used to calculate B violation rates which are found to be generically much faster($\sim 10^{-28}\, yr^{-1}$) than the current experimental limits. Improvements which may allow acceptable B violation rates are identified.

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