arXiv subjects

Zachary Polonsky

Publications and source records attributed to Zachary Polonsky.

15 recordsLinked to original sources

arXiv2026

Current and future constraints on heavy New Physics from $τ$ weak dipole moments

We study the weak magnetic and electric dipole moments of the $τ$ lepton as precision tests of the Standard Model (SM) and probes of heavy New Physics (NP). We present an updated SM prediction for the $τ$ weak magnetic dipole moment at one loop, including a careful assessment of theoretical uncertainties from electroweak scheme dependence. Working within the SM Effective Field Theory, we derive comprehensive current constraints on the $τ$ dipole operators from a combination of observables: the $τ$ weak and electromagnetic dipole moments, high-mass Drell-Yan tails at the LHC, $Z$ partial decay widths, and the electron electric dipole moment. Finally, we assess the prospects of measuring the SM value of the $τ$ weak magnetic moment at the FCC-$ee$ Tera-$Z$ run, and project the sensitivities of the leading observables to heavy NP at FCC-$ee$ and HL-LHC, incorporating informed assumptions about improvements of systematic uncertainties. We find that the $τ$ weak dipole moments are already among the leading probes of the $τ$ dipole operators, and will become increasingly dominant at future colliders.

hep-ph↗

arXiv2025

The Standard Model Prediction for the Rare Decay $B \to X_s ν\bar ν$

We present updated and comprehensive Standard Model predictions for the inclusive rare decay $B \to X_s ν\barν$. Using a state-of-the-art determination of the short-distance coefficient, including NLO QCD and electroweak effects, and implementing a consistent treatment of heavy-quark masses and power corrections within the kinetic scheme, we compute the total decay rate and the neutrino invariant mass spectrum. We incorporate all known perturbative contributions in the heavy quark limit up to $\mathcal{O}(α_s^3)$, evaluate non-perturbative corrections through the Heavy Quark Expansion up to $1/m_b^3$, and include estimates of four-quark operator matrix elements from HQET sum rules. We obtain the Standard Model branching ratios $\text{Br}(B^0 \to X_sν\barν) = (3.35 \pm 0.10)\times 10^{-5} $ and $ \text{Br}(B^+ \to X_sν\barν) = (3.62 \pm 0.11)\times 10^{-5}, $ representing a significant improvement in both central value and precision compared to previous determinations. We also provide predictions for partial rates with kinematic cuts relevant to Belle II. Our results are timely in view of recent measurements of $B \to Kν\barν$ and the first upper limits on inclusive $B \to X_sν\barν$, and they offer a robust baseline for future searches for physics beyond the Standard Model in $b\to sν\barν$ transitions.

hep-ph↗

arXiv2025

Charm rescattering in $B^0\to K^0\bar{\ell}\ell$: an improved analysis

We improve upon previous explicit estimates of charm rescattering contributions to the decay $B^0\to K^0\bar{\ell}\ell$ by including contributions from dipole interactions with the intermediate charm-meson states, and by further investigating the structure of the electromagnetic form factors. Using a model of fundamental meson fields inspired by heavy-hadron chiral perturbation theory, augmented by form factors motivated by theoretical considerations as well as experimental data, we provide a thorough investigation of rescattering contributions induced by intermediate $D^{(*)}D^{(*)}_s$ states.

hep-ph↗

arXiv2025

Time-Dependent Precision Measurement of $B_s^0\rightarrow ϕμ^+μ^-$ Decay at FCC-$ee$

We study the feasibility of measuring time-dependent $C\!P$ violation in the rare flavor-changing neutral current (FCNC) decay $B_s^0 \rightarrow ϕ(\rightarrow K^+K^-) μ^+ μ^-$ at the FCC-$ee$. In the Standard Model (SM), $C\!P$ violation in this mode arises only at higher orders and is highly suppressed. Extensions of the SM, collectively referred to as New Physics (NP), can introduce additional $C\!P$-violating phases that enhance such effects. The decay $B_s^0 \rightarrow ϕμ^+ μ^-$, mediated by the $b \rightarrow s \ell^+ \ell^-$ transition, is therefore a promising probe of NP. The FCC-$ee$, operating as a high-luminosity $Z$-factory, offers an optimal environment for this measurement due to its large event yield, clean conditions, efficient particle identification, and excellent vertex resolution. We perform a Monte Carlo study using Pythia and Delphes with the IDEA detector concept. A relative precision better than $\mathcal{O}(1\%)$ on the branching ratio and $\mathcal{O}(10^{-2})$ on the time-integrated $C\!P$ asymmetry is found to be achievable. We determine the projected sensitivities to the observables $D_f$, $C_f$, and $S_f$, which parameterize time-dependent $C\!P$ violation. In the untagged analysis, a precision of $\mathcal{O}(10^{-1})$ on $D_f$ can be reached. With flavor tagging, sensitivities to $C_f$ and $S_f$ improve to $\mathcal{O}(10^{-2})$. These measurements remain inaccessible to current flavor experiments. Interpreting the results within the Weak Effective Theory provides model-independent constraints on $C\!P$-violating NP. This study demonstrates that FCC-$ee$ enables first-time access to $C\!P$-sensitive observables previously beyond experimental reach.

hep-ph↗

arXiv2025

Explicit estimate of charm rescattering in $B^0 \to K^0 \bar{\ell} \ell$

We analyze $B^0 \to K^0 \bar{\ell}\ell$ long-distance contributions induced by the rescattering of a pair of charmed and charmed-strange mesons. We present an explicit estimate of these contributions using an effective description in terms of hadronic degrees of freedom, supplemented by data on the $B^0 \to D^*D_s (D^*_sD)$ transition in order to reproduce the corresponding discontinuity in the $B^0 \to K^0 \bar{\ell}\ell$ amplitude. The $D^* D_s (D^*_s D) K$ vertex is estimated using heavy-hadron chiral perturbation theory, obtaining an accurate description of the whole rescattering process in the low-recoil (or high-$q^2$) limit. We also present an extrapolation to the whole kinematical region introducing hadronic form factors. The explicit estimate of the leading $D^*D_s (D^*_sD)$ intermediate state leads to a long-distance amplitude which does not exceed a few percent relative to the short-distance one. The consequences of this result for the extraction of the short-distance coefficient $C_9$ are discussed.

hep-ph↗

arXiv2024

A Simple Dirac Prescription for Two-Loop Anomalous Dimension Matrices

A novel method to treat effects from evanescent operators in next-to-leading order (NLO) computations is introduced. The approach allows, besides further simplifications, to discard evanescent-to-physical mixing contributions in NLO calculations. The method is independent of the treatments of $γ_5$ and can therefore be combined with different renormalization schemes. We illustrate the utility of this result by reproducing literature results of two-loop anomalous dimension matrices for both $|ΔF| = 1$ and $|ΔF| = 2$ transitions.

hep-ph↗

arXiv2024

A Precise Electron EDM Constraint on CP-odd Heavy-Quark Yukawas

CP-odd Higgs couplings to bottom and charm quarks arise in many extensions of the standard model and are of potential interest for electroweak baryogenesis. These couplings induce a contribution to the electron EDM. The experimental limit on the latter then leads to a strong bound on the CP-odd Higgs couplings. We point out that this bound receives large QCD corrections, even though it arises from a leptonic observable. We calculate the contribution of CP-odd Higgs couplings to the bottom and charm quarks in renormalisation-group improved perturbation theory at next-to-leading order in the strong interaction, thereby reducing the uncertainty to a few percent.

hep-ph↗

arXiv2024

Renormalization scheme factorization of one-loop Fierz identities

We present a proof of the factorization of renormalization scheme in one-loop-corrected Fierz identities. This scheme factorization facilitates the simultaneous transformation of operator basis and renormalization scheme using only relations between physical operators; the evanescent operators in the respective bases may be chosen entirely independently of each other. The relations between evanescent operators in the two bases is automatically accounted for by the corrected Fierz identities. We illustrate the utility of this result with a two-loop anomalous dimension matrix computation using the Naive-Dimensional Regularization scheme, which is then transformed via one-loop Fierz identities to the known result in the literature given in a different basis and calculated in the Larin scheme. Additionally, we reproduce results from the literature of basis transformations involving the rotation of evanescent operators into the physical basis using our method, without the need to explicitly compute one-loop matrix elements of evanescent operators.

hep-ph↗

arXiv2023

Semi-inclusive $b\to s\bar{\ell}\ell$ transitions at high $q^2$

We present an updated Standard Model (SM) estimate of the inclusive $b\to s\bar{\ell}\ell$ rate at high dilepton invariant mass ($q^2\geq 15~{\rm GeV}^2$). We show that this estimate is in good agreement with the result obtained summing the SM predictions for the leading one-body modes ($K$ and $K^*$) and the subleading non-resonant $Kπ$ channel (for which we also present an updated estimate). On the contrary, the semi-inclusive sum based on data exhibits a deficit compared to the inclusive SM prediction in the muon modes. The statistical significance of this deficit does not exceed $2σ$, but is free from uncertainties on hadronic form factors, and fully compatible with the deficit observed at low-$q^2$ on the exclusive modes. The implications of these results in conjunction with other SM tests on $b\to s\barμμ$ modes are briefly discussed.

hep-ph↗

arXiv2023

Dipole operators in Fierz identities

We study the contribution from dipole operators to one-loop Fierz identities and provide the resulting QCD and QED shifts to the tree-level relations for all four-fermion operators. The results simplify one-loop basis changes as well as matching computations and allow one to consistently eliminate operators from an operator basis which give rise to complications, e.g. traces involving $γ_5$.

hep-ph↗

arXiv2022

Electroweak Corrections to the Charm-Top-Quark Contribution to $ε_K$

We calculate the leading-logarithmic and next-to-leading-logarithmic electroweak corrections to the charm-top-quark contribution to the effective $|ΔS| = 2$ Lagrangian, relevant for the parameter $ε_K$. We find that these corrections lead to a $-0.5\%$ shift in the corresponding Wilson coefficient. Moreover, our calculation removes an implicit ambiguity in the standard-model prediction of $ε_K$, by fixing the renormalization scheme of the electroweak input parameters.

hep-ph↗

arXiv2021

Two-loop Electroweak Corrections to the Top-Quark Contribution to $ε_K$

The parameter $ε_K$ measures $CP$ violation in the neutral kaon system. It is a sensitive probe of new physics and plays a prominent role in the global fit of the Cabibbo-Kobabyashi-Maskawa matrix. The perturbative theory uncertainty is currently dominated by the top-quark contribution. Here, we present the calculation of the full two-loop electroweak corrections to the top-quark contribution to $ε_K$, including the resummation of QED-QCD logarithms. We discuss different renormalization prescriptions for the electroweak input parameters. In the traditional normalization of the weak Hamiltonian with two powers of the Fermi constant $G_F$, the top-quark contribution is shifted by $-1\%$.

hep-ph↗

arXiv2020

Two-loop Beta Function for Complex Scalar Electroweak Multiplets

We present the general form of the renormalizable four-point interactions of a complex scalar field furnishing an irreducible representation of SU(2), and derive a set of algebraic identities that facilitates the calculation of higher-order radiative corrections. As an application, we calculate the two-loop beta function for the SM extended by a scalar multiplet, and provide the result explicitly in terms of the group invariants. Our results include the evolution of the Higgs-portal couplings, as well as scalar "minimal dark matter". We present numerical results for the two-loop evolution of the various couplings.

hep-ph↗

arXiv2019

Thermodynamic phase transitions from dynamical compact dimensions

We perform a double quotient of global AdS$_4$ and study its thermal properties. We find that a double quotient yields a spacetime with an expanding compact dimension. Studying the entanglement of the dual CFT we find that, at early times, the spacetime has thermal properties which disappear after a critical time. For slow expansion, this critical time depends on the expansion rate as expected, but becomes much more sensitive with more rapid expansion rates.

hep-th↗

arXiv2018

Holographic Entanglement Entropy and the (3+1)-dimensional Topological Black Hole

We investigate the Holographic Entanglement Entropy proposal in the context of the (3+1)-dimensional topological black hole. In contrast to the well-studied (2+1)-dimensional case, the maximal extension for this black hole includes only a single exterior region with its conformal boundary. This immediately raises a puzzle as to how one can view the purification of the dual conformal field theory state in terms of a thermofield double in the usual manner. Motivated by this puzzle, we calculate the horizon area for these black holes and discover that the result is observer dependent. This observer dependence poses a potential issue in applying the holographic entropy proposal. Investigating this we find that, although this observer dependence does not carry over to the holographic entanglement entropy, there is an indication of a coordinate system which is best adapted for the holographic calculation. These coordinates only cover two regions of the spacetime which exactly correspond to the regions of the CFT on which particle modes are well defined and so we see that the holographic calculation in the spacetime is capable of predicting regions of the CFT where particles cannot exist.

hep-th↗