arXiv subjects

Gauhar Abbas

Publications and source records attributed to Gauhar Abbas.

At least 19 recordsLinked to original sources

arXiv2026

Naturally Light Composite Higgs as a Protected Collective Eigenmode

Standard routes to a light composite Higgs either rely on tuning a single channel near criticality or protect a pseudo-Nambu--Goldstone coordinate of a coset. We introduce a third mechanism class in which the protected object is an \emph{eigenvalue} of the renormalized multi-operator scalar kernel of the strong sector. Two basis-invariant diagnostics, a sector participation number $\Psec$ and a sector gap ratio $\Rcoll$, identify collective lightness, but they cannot distinguish an accidental small determinant from a protected zero mode; the missing discriminator is the microscopic sensitivity $\Delta_g=\left|\partial\ln|m_H^2|/\partial\ln g\right|$. A protected collective Higgs is defined by $\Rcoll\gg1$, $\Psec>1$, and $\Delta_g=\mathcal{O}(1)$. We prove that this class is nonempty. A rank-one TC--DTC locking invariant forbids tree-level aligned curvature, while universal vectorlike DQCD bridge fermions, massless in the microscopic Lagrangian but acquiring a common DQCD constituent mass, obey $\partial_h^2\sum_A\Tr\mathcal{M}_A^2\big|_0=0$. The aligned scalar is therefore lifted only at joint two-spurion order, $m^2_{\mathrm{br}}=-(d_X/2\pi^2)g_T^2g_D^2(f_B^4/f_H^2)L_X$, giving $\Delta_{g_T}=\Delta_{g_D}=2$ at leading logarithmic order. The same DTC topology admits a collective top completion and a vector-decoupling route to reducing the positive technicolor contribution to $S$. The mechanism is falsifiable by sector-restricted lattice spectroscopy and coupling-response scans.

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arXiv2026

Return of the technicolour

We discuss that conventional Technicolour dynamics can be revitalized within the Dark Technicolour paradigm by invoking the Extended Most Attractive Channel hypothesis. In this framework, Standard Model fermions acquire masses via multifermion chiral condensates arising from new strong dynamics. The model incorporates three confining gauge sectors, Technicolour, Dark Technicolour, and an intermediate QCD-like sector, linked through extended gauge symmetries. The Extended Most Attractive Channel hypothesis reveals a hierarchical structure of condensates, where channels with higher net chirality become increasingly attractive. At low energies, the Dark Technicolour paradigm naturally reduces to the Froggatt-Nielsen or Standard Hierarchical Vacuum Expectation Value model, governed by residual discrete symmetries, offering a compelling resolution to the Standard Model Flavor Problem.

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arXiv2026

Hadronic tau decays at higher orders in QCD

We investigate higher-order perturbative corrections to hadronic $\tau$ decays by applying nonlinear sequence-transformation techniques to the QCD correction $\delta^{(0)}$. In particular, we employ the Shanks transformation and several of its generalisations constructed through Wynn's $\varepsilon$-algorithm, which are known to accelerate the convergence of slowly convergent or divergent series. These methods are used to extract higher-order information from the fixed-order perturbative expansion of $\delta^{(0)}$. Within this framework, we estimate the perturbative coefficients $c_{5,1}$-$c_{12,1}$. In particular, we obtain $c_{5,1}=298 \pm 15$, $c_{6,1}=3431 \pm 256$, and $c_{7,1}=2.29 \pm 0.29\times 10^4$, where the quoted uncertainties reflect the spread among the different sequence transformations employed. Moreover, we predict the QCD correction $ \delta^{(0) }_{\text{FOPT}}=0.2119 \pm 0.0040\pm 0.0065_{\alpha_s} $. Our analysis demonstrates that non-linear sequence transformations, such as the Shanks-type, provide an efficient and systematic tool for probing higher-order perturbative effects in hadronic $\tau$ decays in the absence of explicit multi-loop calculations.

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arXiv2025

A new determination of higher-order QCD corrections to hadronic $\tau$ decays

We employ \textit{Levin-type sequence transformations} to accelerate the convergence of the perturbative fixed-order expansion of the QCD correction $\delta^{(0)}$ in terms of the strong coupling $\alpha_s$. The method efficiently resums the series, yielding a stable and self-consistent determination of higher-order QCD corrections to hadronic $\tau$ decays, consistent with existing results. We find $\delta^{(0)}_{\text{Levin-FOPT}} = 0.2089 \pm 0.0040 \, \pm 0.0060_{\alpha_s} \, $, and predict $ c_{5,1} = 278^{+27}_{-19}, \quad c_{6,1} = 3375^{+489}_{-209}, \quad c_{7,1} = (2.03^{+0.41}_{-0.25}) \times 10^4. $ Our results demonstrate that Levin-type transformations provide an efficient framework for analyzing asymptotic perturbative series, and studying the higher order perturbative behaviour of the hadronic $\tau$ decays.

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arXiv2025

Dark-technicolour at colliders

We demonstrate that QCD-like gauge dynamics can be consistently embedded within the Dark Technicolor paradigm by invoking the extended Most Attractive Channel hypothesis, thereby revitalizing conventional technicolor scenarios. In this framework, the Higgs mass is generated dynamically while remaining consistent with electroweak precision tests, including constraints from the $S$ parameter. The flavor problem is resolved by incorporating the Standard Hierarchical VEVs Model, whereas a simple Froggatt--Nielsen construction is shown to be incompatible. Couplings of techni-hadrons such as $\rho_{\rm TC}$ and $\eta_{\rm TC}^\prime$ to Standard Model fermions are highly suppressed, leading to negligible direct fermionic signatures. Nevertheless, DTC mesons remain testable at the HL-LHC, HE-LHC, and future 100~TeV collider, with promising discovery channels including $\bar{b}b$, $\tau^+\tau^-$, $t\bar{t}$, and $\gamma\gamma$.

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arXiv2025

The standard HVM

We discuss a standard hierarchical VEVs model which predicts the leptonic mixing angles in terms of the Cabibbo angle, and masses of strange and charm quarks as $\sin θ_{12}^\ell \geq 1 - 2 \sin θ_{12}$, $\sin θ_{23}^\ell \geq 1 - \sin θ_{12}$, and $\sin θ_{13}^\ell \geq \sin θ_{12} - \frac{m_s}{m_c}$ for the normal mass ordering of neutrinos. This results in very precise predictions of the leptonic mixing angles given by $\sin θ_{12}^\ell = 0.55 \pm 0.00134 $, $\sin θ_{23}^\ell = 0.775 \pm 0.00067 $, and $\sin θ_{13}^\ell = 0.1413 - 0.1509 $. Furthermore, we predict neutrinos to be the Dirac kind disfavouring the inverted mass hierarchy. The standard hierarchical VEVs model predicts a possible new class of the dark matter candidate, named as neutrinic dark matter.

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arXiv2025

The problem of flavour

We review the problem of flavour tracing back to the days when the standard model was just coming together. We focus on the recently discussed new solutions of this problem, namely the Froggatt and Nielsen mechanism based on a novel discrete $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M}$ flavour symmetry, and the standard hierarchical VEVs model. The standard HVM, and the Froggatt and Nielsen mechanism based on the $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M}$ flavour symmetry, can be recovered from a new dark-technicolour paradigm, where the hierarchical VEVs or the flavon VEV may appear as the chiral multifermion condensates. In particular, there appears a novel feature that the solution of the flavour problem based on the discrete flavour symmetry can provide the so-called flavonic dark matter. This predicts a specific relation between the mass and the symmetry-breaking scale, which can be contrasted with the standard QCD axion. Moreover, a possible direction towards the Grand Unified framework is also discussed.

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arXiv2024

Phenomenology of the standard HVM and 95.4 GeV excess

We investigate the collider phenomenology of the standard Hierarchical VEVs Model by proposing a new version, which avoids large flavor changing neutral current interactions, thus, rendering the scale of new physics as low as the electroweak scale. The resulting collider signatures are distinctive and testable at the High-Luminosity LHC, the High-Energy LHC, and future 100\,TeV hadron colliders. Remarkably, one of the pseudoscalars in the model can account for the 95.4\,GeV di-photon excess observed by ATLAS and CMS. In addition, the model naturally accommodates a new class of neutrino-philic dark matter candidate, \emph{neutrinic dark matter}, that interacts exclusively with neutrino pairs.

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arXiv2024

Finding flavons at colliders

We conduct a comprehensive investigation into the flavour phenomenology and collider signatures of flavon of $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M}$ flavour symmetries for the soft symmetry-breaking scenario and a new symmetry-conserving mechanism at the high-luminosity LHC, high energy LHC, and a 100 TeV hadron collider. The flavour physics of quark and leptonic observables places different bounds on the parameter space of flavons of $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M}$ flavour symmetries. On the collider side, the decay $t \rightarrow c a$ can be probed by the high-luminosity LHC, high energy LHC, and a 100 TeV hadron collider for the $\mathcal{Z}_{\rm 8} \times \mathcal{Z}_{\rm 22}$ flavour symmetry. The inclusive production signatures can be used to probe the flavon of all the $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M} $ flavour symmetries for the soft symmetry-breaking scenario for a heavy flavon at a 100 TeV collider. Flavons of all the $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M} $ flavour symmetries can be probed at high energy LHC and a 100 TeV collider for a low mass in the case of soft symmetry-breaking. The di-flavon production is within reach of the high-luminosity LHC, high energy LHC, and a 100 TeV collider only for a light flavon. The 14 TeV high-luminosity LHC can probe only the $\mathcal{Z}_{\rm 2} \times \mathcal{Z}_{\rm 5}$ and $\mathcal{Z}_{\rm 8} \times \mathcal{Z}_{\rm 22}$ flavour symmetries for a few specific inclusive signatures. The symmetry-conserving scenario remains beyond the detection capabilities of any collider.

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arXiv2024

Discrete origins of matter

We discuss models of the flavour problem and dark matter based on the discrete $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M} \times \mathcal{Z}_{\rm P}$ flavour symmetry. A new class of dark-matter emerges out of these models, which is defined as the flavonic dark matter. An ultra-violet completion of these models based on the dark-technicolour paradigm is also presented.

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arXiv2024

Renormalization-group improved Higgs to two gluons decay rate

We investigate the renormalization-group scale and scheme dependence of the $H \rightarrow gg$ decay rate at the order N$^4$LO in the renormalization-group summed perturbative theory, which employs the summation of all renormalization-group accessible logarithms including the leading and subsequent four sub-leading logarithmic contributions to the full perturbative series expansion. Moreover, we study the higher-order behaviour of the $H \rightarrow gg$ decay width using the asymptotic Padé approximant method in four different renormalization schemes. Furthermore, the higher-order behaviour is independently investigated in the framework of the asymptotic Padé-Borel approximant method where generalized Borel-transform is used as an analytic continuation of the original perturbative expansion. The predictions of the asymptotic Padé-Borel approximant method are found to be in agreement with that of the asymptotic Padé approximant method. Finally, we provide the $H \rightarrow gg$ decay rate at the order N$^5$LO in the fixed-order $ Γ_{\rm N^5LO} \,=\, Γ_0 (1.8375 \pm 0.047 _{α_s(M_Z),1\%}\pm 0.0004_{M_t} \pm 0.0066_{M_H} \pm 0.0036_{\rm P} \pm 0.007_{\text{s}} \pm 0.0005_{sc} ),$ and $Γ_{\rm RGSN^5LO} \,=\, Γ_0 (1.841 \pm 0.047 _{α_s(M_Z),1\%} \pm 0.0005_{M_t}\pm 0.0066_{M_H} \pm 0.0002_μ \pm 0.0027_{\rm P} \pm 0.001_{sc} )$ in the renormalization-group summed perturbative theories.

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arXiv2023

Dark-technicolour at low scale

We discuss a low-scale realization of the dark-technicolour paradigm, where the dark-technicolour scale is close to the electroweak scale. This scenario provides an ultraviolet completion of the standard HVM, and predicts a dark-Higgs with mass $ m_{\rm DH } = 95.4$ GeV. Moreover, the grand-unification scale in this framework can be as low as $1.18 \times 10^8$ GeV.

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arXiv2023

Flavonic dark matter

We first time show that a common solution to dark matter and the flavor problem of the standard model can be obtained in the framework of the $\mathcal{Z}_{\rm N} \times \mathcal{Z}_{\rm M}$ flavor symmetry where the flavonic Goldstone boson of this flavor symmetry acts as a good dark matter candidate through the misalignment mechanism. Hierarchical mass pattern of quarks and charged leptons naturally follows from the discrete symmetry. For light active neutrinos, we construct the Dirac-type mass matrix which is preferred to fit the observed neutrino oscillation data with normal hierarchy. Our model predicts the axion-like photon coupling characteristically different from the standard QCD axion, and could be probed by the future X-ray or radio observations.

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arXiv2023

Flavour bounds on the flavon of a minimal and a non-minimal $\mathcal{Z}_2 \times \mathcal{Z}_N$ symmetry

We investigate flavour bounds on the $\mathcal{Z}_2 \times \mathcal{Z}_5$ and $\mathcal{Z}_2 \times \mathcal{Z}_9$ flavour symmetries. These flavour symmetries are a minimal and a non-minimal forms of the $\mathcal{Z}_2 \times \mathcal{Z}_N$ flavour symmetry, that can provide a simple set-up for the Froggatt-Nielsen mechanism. The $\mathcal{Z}_2 \times \mathcal{Z}_5$ and $\mathcal{Z}_2 \times \mathcal{Z}_9$ flavour symmetries are capable of explaining the fermionic masses and mixing pattern of the standard model including that of the neutrinos. The bounds on the parameter space of the flavon field of the $\mathcal{Z}_2 \times \mathcal{Z}_5$ and $\mathcal{Z}_2 \times \mathcal{Z}_9$ flavour symmetries are derived using the current quark and lepton flavour physics data and future projected sensitivities of quark and lepton flavour effects. The strongest bounds on the flavon of the $\mathcal{Z}_2 \times \mathcal{Z}_5$ symmetry come from the $D^0 - \bar D^0$ mixing. The bounds on the $\mathcal{Z}_2 \times \mathcal{Z}_9$ flavour symmetry are stronger than that of the minimal $\mathcal{Z}_2 \times \mathcal{Z}_5$ symmetry. The ratio $R_{μμ}$ provides rather robust bounds on the flavon parameters in the future phase-\rom{1} and phase-\rom{2} of the LHCb by leaving only a very small region in the allowed parameter space of the models.

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arXiv2022

Origin of the VEVs hierarchy

We present an origin of the VEVs hierarchy in a non-minimal technicolour framework which is capable of explaining the flavour spectrum of the standard model along with neutrino masses and mixing, and simultaneously satisfying crucial experimental bounds. The technicolour scale in this framework can be lower such that a standard model-like Higgs boson emerges from within the model. We also derive lower bound on the mass of the vector technicolour state using the latest experimental bound on the $S$-parameter.

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arXiv2021

A new solution of the fermionic mass hierarchy of the standard model

We present a new mechanism for solving the fermionic masses and mixing hierarchies of the standard model through a minimal symmetry $\mathcal{Z}_2 \times \mathcal{Z}_5$. The mechanism is also capable of explaining the neutrino masses and mixing parameters. The phenomenological bounds arising from kaon mixing are also derived on the parameter space of the model.

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arXiv2019

Solving the fermionic mass hierarchy of the standard model

We show that a simultaneous explanation for fermionic mass hierarchy among and within the fermionic families, quark-mixing, can be obtained in an extension of the standard model, with real singlet scalar fields, which is UV completed by vector-like fermions and a strongly interacting sector.

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arXiv2019

A low scale left-right symmetric mirror model

A left-right symmetric mirror model restoring parity at a high scale in a way such that the mirror fermions and mirror gauge sector simultaneously could exist at TeV scale is discussed. We also provide an ultraviolet completion of the model with vector-like fermions, and discuss some theoretical and phenomenological implications of this model.

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