arXiv subjects

Yuval Grossman

Publications and source records attributed to Yuval Grossman.

At least 37 records · Page 2Linked to original sources

arXiv2023

A Precision Relation between $Γ(K\toμ^+μ^-)(t)$ and ${\cal B}(K_L\toμ^+μ^-)/{\cal B}(K_L\toγγ)$

We find that the phase appearing in the unitarity relation between $\mathcal{B}(K_L\rightarrow μ^+μ^-)$ and $\mathcal{B}(K_L\rightarrow γγ)$ is equal to the phase shift in the interference term of the time-dependent $K\rightarrow μ^+μ^-$ decay. A probe of this relation at future kaon facilities constitutes a Standard Model test with a theory precision of about $2\%$. The phase has further importance for sensitivity studies regarding the measurement of the time-dependent $K\rightarrow μ^+μ^-$ decay rate to extract the CKM matrix element combination $\vert V_{ts} V_{td} \sin(β+β_s)\vert\approx A^2λ^5\barη$. We find a model-independent theoretically clean prediction, $\cos^2φ_0 = 0.96 \pm 0.03$. The quoted error is a combination of the theoretical and experimental errors, and both of them are expected to shrink in the future. Using input from the large-$N_C$ limit within chiral perturbation theory, we find a theory preference towards solutions with negative $\cosφ_0$, reducing a four-fold ambiguity in the angle $φ_0$ to a two-fold one.

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arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

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arXiv2023

Fermion pair radiation from accelerating classical systems

Accelerating classical systems that couple to a fermion-antifermion pair at the microscopic level can radiate pairs of fermions and lose energy in the process. In this work, we derive the generalization of the Larmor formula for fermion pair radiation. We focus on the case of a point-like classical source in an elliptical orbit that emits fermions through vector and scalar mediators. Ultra-light fermion emission from such systems becomes relevant when the mass of the mediator is larger than the frequency of the periodic motion. This enables us to probe regions of the parameter space that are inaccessible in on-shell bosonic radiation. We apply our results to pulsar binaries with mediators that couple to muons and neutrinos. Using current data on binary period decays, we extract bounds on the parameters of such models.

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arXiv2022

The branching fraction of $B_s\to K^0\bar K^0$: Three puzzles

The branching fraction of the $B_s\to K^0\bar K^0$ decay has been recently measured by the LHCb and Belle experiments. We study the consistency of the measured value with three relations to other decay rates and CP asymmetries which follow from the Standard Model, and from the approximate flavor $SU(3)$ symmetry of the strong interactions. We find that each of these relations is violated at a level of above $3σ$. We argue that various subleading effects -- rescattering, electroweak penguins and $SU(3)$ breaking -- if larger than theoretically expected, can account for some of these puzzles, but not for all of them simultaneously.

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arXiv2022

CP violation in $b$ and $c$ quark decays

Generically, non-Standard-Model particles contribute to processes with order-one charge-parity (CP) violating phases, as CP is not a fundamental symmetry of nature. The exploration of CP violation becomes therefore a sensitive search for non-Standard-Model physics. We briefly review the current status of CP-violation studies in bottom- and charm-quark transitions focusing on those quantities that are most sensitive to non-Standard-Model contributions and discuss opportunities and challenges for the next decade and beyond.

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arXiv2022

The Mathematical Structure of $U$-Spin Amplitude Sum Rules

We perform a systematic study of $SU(2)$ flavor amplitude sum rules with particular emphasis on $U$-spin. This study reveals a rich mathematical structure underlying the sum rules that allows us to formulate an algorithm for deriving all $U$-spin amplitude sum rules to any order of the symmetry breaking. This novel approach to deriving the sum rules does not require one to explicitly compute the Clebsch-Gordan tables, and allows for simple diagrammatic interpretation. Several examples that demonstrate the application of our novel method to systems that can be probed experimentally are provided.

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arXiv2022

CKM substructure from the weak to the Planck scale

We look for relations among CKM matrix elements that are not consequences of the Wolfenstein parametrization. In particular, we search for products of CKM elements raised to integer powers that approximately equal $1$. We study the running of the CKM matrix elements and resolve an apparent discrepancy in the literature. To a good approximation only $A$ runs, among the Wolfenstein parameters. Using the Standard Model renormalization group we look for CKM relations at energy scales ranging from the electroweak scale to the Planck scale, and we find 19 such relations. These relations could point to structure in the UV, or be numerical accidents. For example, we find that $| V_{td} V_{us} | = | V_{cb}^2 |$, within $2\%$ accuracy, in the $10^9$-$10^{15}$ GeV range. We discuss the implications of this CKM relation for a Yukawa texture in the UV.

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arXiv2021

Theoretical challenges for flavor physics

We discuss some highlights of the FCC-ee flavor physics program. It will help to explore various aspects of flavor physics: to test precision calculations, to probe nonperturbative QCD methods, and to increase the sensitivity to physics beyond the standard model. In some areas, FCC-ee will do much better than current and near-future experiments. We briefly discuss several probes that can be relevant for maximizing the gain from the FCC-ee flavor program.

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arXiv2021

$K\to μ^{+} μ^{-}$ as a clean probe of short-distance physics

The $K\toμ^+μ^-$ decay is often considered to be uninformative of fundamental theory parameters since the decay is polluted by long-distance hadronic effects. We demonstrate that, using very mild assumptions and utilizing time-dependent interference effects, ${\cal B}(K_S\toμ^+μ^-)_{\ell=0}$ can be experimentally determined without the need to separate the $\ell=0$ and $\ell=1$ final states. This quantity is very clean theoretically and can be used to test the Standard Model. In particular, it can be used to extract the CKM matrix element combination $\left|V_{ts}V_{td}\sin(β+β_s)\right|\approx |A^2 λ^5 \bar η|$ with hadronic uncertainties below $1\%$.

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arXiv2021

Probing the $ΔU=0$ Rule in Three Body Charm Decays

CP violation in charm decay was observed in the decays $D^0\rightarrow P^{\pm}P^{\mp}$ of a $D^0$ meson to two pseudoscalars. When interpreted within the SM, the results imply that the ratio of the relevant rescattering amplitudes has a magnitude and phase that are both of $O(1)$. We discuss ways to probe similar ratios in $D^0\rightarrow V^{\pm}P^{\mp}$ decays, where $V$ is a vector that decays to two pseudoscalars, from the Dalitz-plot analysis of time-integrated three-body decays. Compared to two-body decays, three-body decays have the advantage that the complete system can be solved without the need for time-dependent CP violation measurements or use of correlated $D^0$--$\overline{D}^0$ production. We discuss the decays $D^0\rightarrow π^+π^-π^0$ and $D^0\rightarrow K^+K^-π^0$ as examples by considering a toy model of only two overlapping charged resonances, treating the underlying pseudo two-body decays in full generality.

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arXiv2020

Probing the two-neutrino exchange force using atomic parity violation

The exchange of two neutrinos at one loop leads to a long-range parity-violating force between fermions. We explore the two-neutrino force in the backdrop of atomic physics. We point out that this is the largest parity-violating long-range force in the Standard Model and calculate the effect of this force in experiments that probe atomic parity violation by measuring optical rotation of light as it passes through a sample of vaporized atoms. We perform explicit calculations for the hydrogen atom to demonstrate this effect. Although we find that the effect is too small to be observed in hydrogen in the foreseeable future, our approach may be applied to other setups where long-range parity violation is large enough to be probed experimentally.

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arXiv2020

CKM Substructure

The CKM matrix is not generic. The Wolfenstein parametrization encodes structure by having one small parameter, $λ\approx 0.22$. We pose the question: is there substructure in the CKM matrix that goes beyond the single small parameter of the Wolfenstein parameterization? We find two relations that are approximately satisfied: $|V_{td}|^2 = |V_{cb}|^3$ and $|V_{ub}|^2 |V_{us}| = |V_{cb}|^4$. We discuss the statistical significance of these relations and find that they may indicate deeper structure in the CKM matrix. The current precision, however, cannot exclude an $\mathcal{O}(10 \%)$ accident.

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arXiv2020

On the Statistical Treatment of the Cabibbo Angle Anomaly

We point out that testing the equality of the Cabibbo angle as extracted from $Γ(K\rightarrow πlν)$, the ratio $Γ(K\rightarrow lν)/Γ(π\rightarrow lν)$ and nuclear $β$ decays is not identical to a test of first row unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The reason is that a CKM unitarity test involves only two parameters, while the degrees of freedom for the assessment of the goodness-of-fit of the universality of the Cabibbo angle entailed by the Standard Model (SM) is equal to the number of measurements minus one. Beyond the SM all different processes could in principle give different Cabibbo angles. Consequently, the difference between the two tests becomes relevant starting from three observables giving results for the Cabibbo angle that are in tension with each other. With current data, depending on the treatment of the nuclear $β$ decays, we find that New Physics is favored over the SM at $5.1\,σ$ or $3.6\,σ$ while CKM unitarity is rejected at $4.8σ$ or $3.0σ$, respectively. We argue that the best method to test the SM is to test the equality of the Cabibbo angle, because CKM unitarity is only one aspect of the SM.

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arXiv2020

SU(3)$_F$ Analysis for Beauty Baryon Decays

We perform a general SU(3)$_F$ analysis of $b\rightarrow c\bar{c}s(d)$ decays of members of the beauty baryon antitriplet to a member of the light baryon octet and a singlet. Under several reasonable assumptions we found $\left\vert \mathcal{A}(Ξ_b^0\rightarrow ΛS)/ \mathcal{A}(Ξ_b^0\rightarrow Ξ^0 S)\right\vert\approx 1/\sqrt{6}\, \left\vert V_{cb}^* V_{cd} / (V_{cb}^* V_{cs})\right\vert$ and $\left\vert\mathcal{A}(Λ_b\rightarrow Σ^0 S)/\mathcal{A}(Λ_b\rightarrow ΛS)\right\vert \sim 0.02$. These two relations have been recently probed by LHCb for the case of $S=J/ψ$. The former agrees with the measurement, while for the latter our prediction lies close to the upper bound set by LHCb.

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arXiv2019

The Emergence of the $ΔU=0$ Rule in Charm Physics

We discuss the implications of the recent discovery of CP violation in two-body SCS $D$ decays by LHCb. We show that the result can be explained within the SM without the need for any large $SU(3)$ breaking effects. It further enables the determination of the imaginary part of the ratio of the $ΔU=0$ over $ΔU=1$ matrix elements in charm decays, which we find to be $(0.65\pm 0.12)$. Within the standard model, the result proves the non-perturbative nature of the penguin contraction of tree operators in charm decays, similar to the known non-perturbative enhancement of $ΔI=1/2$ over $ΔI=3/2$ matrix elements in kaon decays, that is, the $ΔI=1/2$ rule. As a guideline for future measurements, we show how to completely solve the most general parametrization of the $D \to P^+P^-$ system.

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arXiv2019

Measuring CP violation in $b\to cτ^-\barν_τ$ using excited charm mesons

There is growing evidence for deviation from the standard model predictions in the ratios between semi-tauonic and semi-leptonic $B$ decays, known as the $R(D^{(*)})$ puzzle. If the source of this non-universality is new physics, it is natural to assume that it also breaks CP symmetry. In this paper we study the possibility of measuring CP violation in semi-tauonic $B$ decays, exploiting interference between excited charm mesons. Given the current values of $R(D^{(*)})$, we find that our proposed CP-violation observable could be as large as about 10%. We discuss the experimental advantages of our method and propose carrying it out at Belle II and LHCb.

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arXiv2018

U-Spin Sum Rules for CP Asymmetries of Three-Body Charmed Baryon Decays

Triggered by a recent LHCb measurement and prospects for Belle II, we derive U-spin symmetry relations between integrated CP asymmetries of three-body $Λ_c^+$ and $Ξ_c^+$ decays. The sum rules read $A_{CP}(Λ_c^+\rightarrow p K^- K^+) + A_{CP}(Ξ_c^+\rightarrow Σ^+ π^- π^+) = 0$, $A_{CP}(Λ_c^+\rightarrow p π^- π^+) + A_{CP}(Ξ_c^+\rightarrow Σ^+ K^- K^+) = 0$, and $A_{CP}(Λ_c^+\rightarrow Σ^+ π^- K^+) + A_{CP}(Ξ_c^+\rightarrow pK^-π^+) = 0$. No such U-spin sum rule exists between $A_{CP}(Λ_c^+\rightarrow p K^- K^+)$ and $A_{CP}(Λ_c^+\rightarrow p π^- π^+)$. All of these sum rules are associated with a complete interchange of $d$ and $s$ quarks. Furthermore, there are no U-spin CP asymmetry sum rules which hold to first order U-spin breaking.

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arXiv2018

Re-visiting the bounds on hydrogen-antihydrogen oscillations from diffuse $γ$-ray surveys

Surveys of diffuse $γ$-ray in the interstellar medium (ISM) can be used to probe hydrogen-antihydrogen oscillations, by detecting the $γ$-ray emission from antihydrogen annihilation. A bound on the oscillation parameter $δ$ was originally derived by Feinberg, Goldhaber and Steigman (1978). In this paper, we re-visit the original derivation by performing a more detailed analysis that (1) incorporates suppression effects from additional elastic and inelastic processes, (2) treats the ISM as a multi-phase medium, and (3) utilises more recent $γ$-ray data from the Fermi Large Area Telescope. We find that suppression from elastic scattering plays a more important role than previously thought, while the multi-phase nature of the ISM affects how the $γ$-ray data should be utilised. We derive a more accurate bound on the oscillation period that is about an order of magnitude weaker than the older bound.

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