arXiv subjects

Ajay Kaladharan

Publications and source records attributed to Ajay Kaladharan.

12 recordsLinked to original sources

arXiv2026

Quantum Tomography and Entanglement in Semi-Leptonic $h\to VV^*$ Decays at Higher Orders

Angular correlations in Higgs decays to electroweak gauge bosons, $h \to ZZ^*, WW^*$, provide a powerful probe of both new physics effects and quantum information observables. We present a systematic study of semi-leptonic Higgs decays $h \to V V^* \to \ell^+\ell^- q\bar{q}$ and $\ell^\pm \nu_\ell q\bar{q}'$, including finite final state fermion masses, NLO QCD, and NLO electroweak corrections. We show that finite final state quark masses can induce effects that go beyond the two-qutrit description in more inclusive regimes, while remaining controllable with suitable kinematic selections. QCD corrections lead to modest percent-level shifts, whereas electroweak corrections can significantly modify the angular structure, particularly in the $h\to ZZ^*$ channels. We assess the impact of these effects on the reconstructed density matrix and entanglement measures, finding that, although they modify the angular observables, the semi-leptonic channels are better approximated by a two-qutrit description than the fully leptonic decay $h\to e^+e^-\mu^+\mu^-$.

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arXiv2025

Dirac Leptogenesis in Left-Right Symmetric Models

Left-right symmetric models which employ a generalized seesaw mechanism to generate quark and charged lepton masses are known to solve the strong CP problem via parity symmetry, without the need for the axion. These models lead to naturally light Dirac neutrinos with their masses arising through radiatve corrections. In this work, we show how baryogenesis via Dirac leptogenesis can be implemented in this framework. A pair of left-right symmetric scalar doublets $ϕ_{L,R}$ carrying $(B-L)$ charge of $3$ is introduced for this purpose, which preserves the parity solution to the strong CP problem. Small neutrino masses are generated through one-loop diagrams mediated by these scalars. The decay of vector-like leptons ($E_i$) involved in the seesaw mechanism to generate charged lepton masses, $E_i \rightarrow \overlineν_{jR} \,ϕ_R^-$, creates a right-handed neutrino ($ν_{R}$) asymmetry, while preserving total lepton number. The compensating lepton asymmetry is converted to baryon asymmetry via electroweak sphalerons. We show that for a large range of model parameters successful baryogenesis can be realized, with the $W_R^\pm$ gauge boson mass of order $10^{11}$ GeV.

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arXiv2025

Higher-Order Corrections to Quantum Observables in $h\to WW^*$

The Higgs boson decay $h \to WW^* \to \ell^+ \nu_\ell \ell'^- \bar{\nu}_{\ell'}$ provides a unique window into the structure of the Higgs couplings to electroweak gauge bosons and has recently gained attention for its potential to unveil quantum properties such as quantum entanglement between the intermediate gauge bosons. In this work, we present a systematic study of next-to-leading order electroweak corrections to the angular coefficients characterizing this decay. While these coefficients are highly constrained at leading order, radiative corrections induce shifts of up to 5% to the existing terms and generate novel structures that vanish at leading order, breaking previous relations among coefficients. While higher-order effects influence the results, the two-qutrit quantum structure in the $h\to WW^*$ channel exhibits greater stability under such corrections than in the previously studied $h \to ZZ^*$ decay.

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arXiv2025

Quantum Entanglement is Quantum: ZZ Production at the LHC

Polarization and spin correlations in diboson systems serve as powerful tools for precision tests and searches for new physics. Recently, interpreting these observables through the lens of quantum information, for instance by examining whether the diboson systems exhibit entanglement, has introduced a compelling new dimension to these studies. We analyze the angular coefficients in the processes $pp\to e^+e^-\mu^+\mu^-$ and $h\to e^+e^-\mu^+\mu^-$, incorporating higher-order QCD and electroweak corrections. Guided by the fundamental properties of the spin density matrix, we assess the stability of the two-qutrit interpretation under radiative effects. For the $pp \to e^+e^-\mu^+\mu^-$ process, NLO QCD corrections preserve the two-qutrit structure but weaken entanglement indicators, an effect that can be partially mitigated by jet binning. In contrast, electroweak corrections introduce non-factorizable contributions that modify the quantum properties of the system. While these effects can be largely depleted by selecting events with a double-resonant $ZZ$ structure, such a kinematic handle is not available for Higgs decays. In the $h \to e^+e^-\mu^+\mu^-$ channel, singly-resonant NLO electroweak corrections substantially distort the angular coefficients, challenging the description of these events as a two-qutrit system.

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arXiv2025

Primordial Black Holes from First-Order Phase Transition in the xSM

Supercooled first-order phase transition (FOPT) can lead to the formation of primordial black holes (PBHs). This scenario imposes stringent requirements on the profile of the effective potential. In this work, we use the singlet extended Standard Model (xSM) as a benchmark model to investigate this possibility at the electroweak scale. The PBHs formed during a supercooled FOPT have a narrow mass distribution around the mass of Earth. This distribution is closely tied to the temperature at which the PBHs form, corresponding to the FOPT at the electroweak scale. This scenario can be probed with microlensing experiments, space-based gravitational wave detectors, and collider experiments. Remarkably, the future space-based gravitational wave detector LISA will hold the potential to either confirm this PBH scenario in the xSM or completely rule it out for extremely small total dark matter fraction made of PBHs, down to $f_{\rm PBH}> 10^{-300}$. Interestingly, our findings suggest that PBHs within the xSM framework may align with observations of the six ultrashort timescale events reported by the OGLE microlensing experiment.

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arXiv2024

Unified Origin of Inflation, Baryon Asymmetry, and Neutrino Mass

In this work, we present a unified theoretical framework that simultaneously addresses some of the most intriguing puzzles in particle physics and cosmology, namely the origins of neutrino mass, baryon asymmetry, and cosmic inflation. In our model, inflation is driven by a combination of the Standard Model Higgs, the type II seesaw Higgs responsible for neutrino mass generation, and the unified symmetry-breaking Higgs field. During inflation, non-zero values of the latter field ensure the absence of the monopole problem. The baryon asymmetry is generated through the Affleck-Dine mechanism, facilitated by the non-zero angular motion in the phase of a complex scalar field, which is part of the inflaton. We find that the successful parameter region for generating baryon asymmetry through a renormalizable term in the scalar potential requires a rather heavy type II seesaw triplet, with a mass well beyond the TeV scale. Inflationary observables, in particular, the spectral index is in excellent agree with experimental observation, whereas tensor-to scalar ratio is expected to be probed by the future LiteBIRD and CMB-S4 missions.

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arXiv2024

Gravitational Wave Signatures of a Chiral Fermion Dark Matter Model

Theories in which the dark matter (DM) candidate is a fermion transforming chirally under a gauge symmetry are attractive, as the gauge symmetry would protect the DM mass. In such theories, the universe would have undergone a phase transition at early times that generated the DM mass upon spontaneous breaking of the gauge symmetry. In this paper, we explore the gravitational wave signals of a simple such theory based on an $\mathrm{SU}(2)_\mathrm{D}$ dark sector with a dark isospin-$3/2$ fermion serving as the DM candidate. This is arguably the simplest chiral theory possible. The scalar sector consists of a dark isospin-$3$ multiplet which breaks the $\mathrm{SU}(2)_\mathrm{D}$ gauge symmetry and also generates the DM mass. We construct the full thermal potential of the model and identify regions of parameter space which lead to detectable gravitational wave signals, arising from a strong first-order $\mathrm{SU}(2)_\mathrm{D}$ phase transition, in various planned space-based interferometers, while also being consistent with dark matter relic abundance. Bulk of the parameter space exhibiting detectable gravitational wave signals in the model also has large WIMP-nucleon scattering cross sections, $σ_{\rm SI}$, which could be probed in upcoming direct detection experiments.

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arXiv2024

Fermion mass, Axion dark matter, and Leptogenesis in SO(10) GUT

SO(10) grand unified theory with minimum parameters in the Yukawa sector employs the Peccei-Quinn symmetry that solves the strong CP problem. Such an economical Yukawa sector is highly appealing and has been extensively studied in the literature. However, when the running of the renormalization group equations of the Yukawa couplings are considered, this scenario shows somewhat tension with the observed fermion masses and mixing. In this work, we propose an extension of the minimal framework that alleviates this tension by introducing only a few new parameters. The proposed model consists of a fermion in the fundamental and a scalar in the spinorial representations. While the latter is needed to implement the Peccei-Quinn symmetry successfully, the presence of both is essential in obtaining an excellent fit to the fermion mass spectrum. In our model, axions serve the role of dark matter, and the out-of-equilibrium decays of the right-handed neutrinos successfully generate the matter-antimatter symmetry of the Universe.

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arXiv2023

Gravitational Waves, Bubble Profile, and Baryon Asymmetry in the Complex 2HDM

This study explores the generation of the observed baryon asymmetry of the Universe within the complex Two Higgs Doublet Model (C2HDM) while considering theoretical and current experimental constraints. In our investigation, we analyze critical elements of the Higgs potential to understand the phase transition pattern. Specifically, we examine the formation of the barrier and the uplifting of the true vacuum state, which play crucial roles in facilitating a strong first-order phase transition. Furthermore, we explore the potential gravitational wave signals associated with this phase transition pattern and investigate the parameter space points that can be probed with LISA. Finally, we compare the impact of different approaches to describing the bubble profile on the calculation of the baryon asymmetry. We contrast the typically used kink profile approximation against the explicit solution of the tunneling profile. We find that a non-negligible range of the C2HDM parameter space results in significant discrepancies in the baryon asymmetry estimation between these two approaches. Through an examination of the parameter space, we identify a benchmark point that satisfies the observed baryon asymmetry.

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arXiv2023

Resonant top pair searches at the LHC: a window to electroweak phase transition

The dynamics of electroweak phase transition could have profound consequences for particle physics and cosmology. We study the prospects for the HL-LHC to probe the strong first-order electroweak phase transition (SFOEWPT) regime in the type-I 2HDM. We focus on the Higgstrahlung channel $pp\to ZH/A$ with a resonant top-quark pair final state $H/A\to t\bar t$. We find that the top-quark pair final state renders the largest sensitivity to the SFOEWPT regime, in comparison to the other Higgstrahlung searches already performed by ATLAS and CMS, that focus on the $H/A\to bb$ and $H\to WW$ final states. We also derive the complementarity of the Higgstrahlung searches with other relevant classes of searches at the HL-LHC and compare them with the gravitational wave sensitivity at LISA.

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arXiv2022

Gravitational Wave Imprints of Left-Right Symmetric Model with Minimal Higgs Sector

We study the gravitational wave imprints of left-right symmetric model equipped with universal seesaw mechanism allowing for the natural generation of hierarchical masses of the Standard Model fermions. The scalar sector of this model is the minimal one, consisting of only two Higgs doublets. Following the construction of the full thermal potential for this model, we perform a scan of the entire parameter space and identify the region in which the cosmic phase transition associated with the left-right symmetry breaking gives gravitational wave signals detectable by a variety of planned space-based interferometers. Then we also discuss the relevant collider implications of this beyond the Standard Model scenario.

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arXiv2021

Electroweak phase transition in the 2HDM: Collider and gravitational wave complementarity

The knowledge of the Higgs potential is crucial for understanding the origin of mass and the thermal history of our Universe. We show how collider measurements and observations of stochastic gravitational wave signals can complement each other to explore the multiform scalar potential in the two Higgs doublet model (2HDM). Accounting for theoretical and current experimental constraints, we analyze the key ingredients in the shape of the Higgs potential triggering the transmutation in phase transition, from the smooth crossover to the strong first-order phase transition ($\xi_c>1$), focusing on the barrier formation and the upliftment of the true vacuum. In particular, we observe that the $\xi_c>1$ regime is favored for lower scalar masses, rendering strong extra motivation for collider searches. We contrast the dominant collider signals at the HL-LHC (high-luminosity LHC) with observable gravitational wave signals at LISA. We obtain that the HL-LHC will be able to cover a vast range of the $\xi_c>1$ parameter space, with scalar decays to heavy fermions $(H,A,H^\pm\to tt, tb)$ being the most promising smoking gun signature of a strong first-order electroweak phase transition in the 2HDM.

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