arXiv subjects

Alexandre Carvunis

Publications and source records attributed to Alexandre Carvunis.

7 recordsLinked to original sources

arXiv2026

New Physics in inclusive $\bar{B} \to X_c \ell \bar{\nu}$ decays

We present the first global phenomenological fit of inclusive $\bar B\to X_c\ell\bar\nu$ observables to all available experimental data allowing for generic dimension-six New Physics interactions in the Weak Effective Theory. The fit includes both New Physics Wilson coefficients and non-perturbative QCD parameters. New Physics contributions are calculated including power corrections up to $\mathcal O(\Lambda_{\rm QCD}^3/m_b^3)$ and perturbative QCD corrections up to $\mathcal O(\alpha_s)$. We find no significant preference for New Physics and obtain bounds on the size of the relevant Wilson Coefficients competitive with those coming from exclusive modes.

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arXiv2026

One-Loop QCD Corrections to $\bar{B}\to X_c \ell \bar{\nu}_\ell$ in and Beyond the Standard Model

We compute one-loop QCD corrections to the triple differential width of the inclusive decay $\bar{B} \to X_c \ell \bar{\nu}_\ell$ including contributions from all relevant dimension-six operators in the Weak Effective Theory (WET), at leading power in heavy quark expansion. Furthermore we derive for the first time up to order $\mathcal{O}(\alpha_s)$ analytic expressions for the first three moments of the distribution in the lepton energy, hadronic invariant mass and dilepton invariant mass, in the presence of beyond the Standard Model contributions from the WET.

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arXiv2025

New Physics in inclusive semileptonic $B$ decays

We study inclusive semileptonic $\bar{B}\to X_c \ell \bar{\nu}$ decays ($\ell = e,\mu$) in the presence of generic physics Beyond the Standard Model (BSM) that is heavy compared to the $b$-quark mass. Its effect is encoded in the Wilson coefficients of dimension-six operators of the Weak Effective Theory (WET). We compute the resulting BSM contributions to the experimentally measured kinematic moments and the total decay rate through order $\mathcal{O}(\Lambda_{\rm QCD}^3/m_b^3)$ in the Heavy Quark Expansion, as well as the $\mathcal{O}(\alpha_s)$ corrections for the right-handed vector current. We then perform fits to the full set of available inclusive measurements in several single-mediator scenarios and in the full WET basis. We find qualitatively new bounds in several of these scenarios, complementary to and competitive with constraints from exclusive decays.

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arXiv2022

Relic Challenges for Vector-Like Fermions as Connectors to a Dark Sector

New dark sectors consisting of exotic fields that couple only very feebly to the Standard Model (SM) have strong theoretical motivation and may be relevant to explaining the abundance of dark matter (DM). An important question for such sectors is how they connect to the SM. For a dark sector with a new gauge interaction, a natural connection arises from heavy vector-like fermions charged under both the visible and dark gauge groups. The gauge charges of such fermions imply that one or more of them is stable in the absence of additional sources of dark symmetry breaking. A generic challenge for such connectors is that they can produce too much dark matter or interact too strongly with nuclei if they were ever thermalized in the early universe. In this paper we study this challenge in a simple connector theory consisting of new vector-like electroweak doublet and singlet fermions that also transform under the fundamental representation of a new (Abelian) gauge force, and we show that these connectors in their minimal form are almost always ruled out by existing direct DM searches. To address this challenge, we investigate two solutions. First, we study mitigating scattering on nuclei by introducing a Majorana mass term for the singlet. And second, we investigate a mixing with SM leptons that allows the connectors to decay while remaining consistent with cosmological tests and searches for charged lepton flavor violation. Both solutions rely on the presence of a dark Higgs field with a specific charge.

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arXiv2022

The Forward-Backward Asymmetry in $B\to D^{*}\ellν$: One more hint for Scalar Leptoquarks?

Experimental data have provided intriguing hints for the violation of lepton flavour universality (LFU), including $B\to D^{(*)}τν/B\to D^{(*)}\ellν$, the anomalous magnetic moment of the muon and $b\!\to\! s\ell^+\ell^-$ with a significance of $\!>3\,σ$, $>\!4\,σ$ and $>\!5\,σ$, respectively. Furthermore, in a recent re-analysis of 2018 Belle data, it was found that the forward-backward asymmetry ($ΔA_{\rm FB}$) of $B \to D^{*}μ\bar ν$ vs $B\to D^{*}e\bar ν$ disagrees with the SM prediction by $\approx\!\!4\,σ$, providing an additional sign of LFU violation. We show that a tensor operator is necessary to significantly improve the agreement with data in $ΔA_{\rm FB}$ while respecting the bounds from other $b\to c\ellν$ observables. Importantly, this tensor operator can only be induced (at tree-level within renormalizable models) by a scalar leptoquark. Furthermore, among the two possible representations, the $SU(2)_L$-singlet $S_1$ and the doublet $S_2$, which can interestingly both also account for the anomalous magnetic moment of the muon, only $S_1$ can provide a good fit. Even though the constraints from (differences of) other angular observables prefer a smaller value of $ΔA_{\rm FB}$ than the current central one, this scenario is significantly preferred (nearly $4 σ$) over the SM hypothesis, and is compatible with constraints such as $B\to K^*νν$ and electroweak precision bounds. Therefore, if the $ΔA_{\rm FB}$ anomaly is confirmed, it would provide circumstantial evidence for scalar leptoquarks and pave the way for a natural connection with all other anomalies pointing towards LFU violation.

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arXiv2021

On the effective lifetime of $B_s \to μμγ$

We consider the $B^0_s \to μ^{+} μ^{-} γ$ effective lifetime, and the related CP-phase sensitive quantity $A_{ΔΓ_s}^{μμγ}$, as a way to obtain qualitatively new insights on the current $B$-decay discrepancies. Through a fit comparing pre- to post-Moriond-2021 data we identify a few theory benchmark scenarios addressing these discrepancies, and featuring large CP violation in addition. We then explore the possibility of telling apart these scenarios with $A_{ΔΓ_s}^{μμγ}$, once resonance-modeling and form-factor uncertainties are taken into account. We do so in both regions of low and high invariant di-lepton mass-squared $q^2$. For low $q^2$, we show how to shape the integration range in order to reduce the impact of the $ϕ$-resonance modelling on the $A_{ΔΓ_s}^{μμγ}$ prediction. For high $q^2$, we find that the corresponding pollution from broad-charmonium resonances has a surprisingly small effect on $A_{ΔΓ_s}^{μμγ}$. This is due to a number of cancellations, that can be traced back to the complete dominance of semi-leptonic operator contributions for high $q^2$ -- at variance with low $q^2$ -- and to $A_{ΔΓ_s}^{μμγ}$ behaving like a ratio-of-amplitudes observable. Our study suggests that $A_{ΔΓ_s}^{μμγ}$ is -- especially at high $q^2$ -- a potentially valuable probe of short-distance CP-violating effects in the very same Wilson coefficients that are associated to current $b \to s$ discrepancies. Its discriminating power, however, relies on progress in form-factor uncertainties. Interestingly, high $q^2$ is the region where $B^0_s \to μ^{+} μ^{-} γ$ is already being accessed experimentally, and the region where form factors are more accessible through non-perturbative QCD methods.

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arXiv2020

Composite Dark Matter and a horizontal symmetry

We present a model of composite Dark Matter (DM), in which a new QCD-like confining "hypercolor" sector generates naturally stable hyperbaryons as DM candidates and at the same time provides mass to new weakly coupled gauge bosons $H$ that serve as DM mediators, coupling the hyperbaryons to the Standard Model (SM) fermions. By an appropriate choice of the $H$ gauge symmetry as a horizontal $SU(2)_h$ SM flavor symmetry, we show how the $H$ gauge bosons can be identified with the horizontal gauge bosons recently put forward as an explanation for discrepancies in rare $B$-meson decays. We find that the mass scale of the $H$ gauge bosons suggested by the DM phenomenology intriguingly agrees with the one needed to explain the rare $B$-decay discrepancies.

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