arXiv subjects

Yosef Nir

Publications and source records attributed to Yosef Nir.

At least 19 recordsLinked to original sources

arXiv2026

CP asymmetries in charged meson decay to two pions

We study the CP asymmetries in $B^+$, $D^+$, and $K^+$ decays into $\pi^+\pi^0$. These asymmetries are commonly known to vanish in the isospin limit. We clarify what is meant by the term ``isospin limit" in this context. We provide a unified formalism to discuss these asymmetries, and develop an understanding of how various suppression factors distinguish between them qualitatively. We estimate the size of the asymmetries in the Standard Model: $A_{CP}(B^+\to\pi^+\pi^0)\sim 3\times10^{-3}$, $A_{CP}(D^+\to\pi^+\pi^0)\sim 10^{-5}$, and $A_{CP}(K^+\to\pi^+\pi^0)\sim 10^{-6}$

hep-ph↗

arXiv2025

Chasing the muon EDM to constrain the SMEFT and UV models

Following a proposal for an experiment with sensitivity to an electric dipole moment (EDM) of the muon $d_\mu$ of order $6\times10^{-23}\ e$ cm, three to four orders of magnitude below the current bound, but still seven orders of magnitude above the current bound on the EDM of the electron $d_e$, we explore the discovery potential of such an experiment. Within the dimension-six CP violating operators of the Standard Model effective field theory (SMEFT), we identify two dipole operators where $d_\mu$ has the strongest sensitivity, and four classes of four-fermion operators where it has the best sensitivity for regions of parameter space that are far from minimal flavor violation. We further consider three UV completions: vector-like leptons (VLLs), heavy vector boson with off-diagonal leptonic couplings, and two Higgs doublet model. For each, we identify the region in parameter space that will be uniquely explored by the proposed $d_\mu$ experiment. In case of VLLs, we also find measurements of $\Gamma (h \rightarrow \mu \mu)$ offer competitive sensitivity, highlighting the complementary role of collider observables. Generically, the potential reach is to ${\cal O}(10\ {\rm TeV})$ scale of new physics.

hep-ph↗

arXiv2025

Lessons from LHCb and Belle II measurements of $B\to J/\psi \pi$ and $B\to J/\psi K$ decays

The LHCb collaboration has recently measured the CP asymmetry in $B^+\to J/\psi\pi^+$ decay, while the Belle II collaboration has recently measured the CP asymmetries in $B^0\to J/\psi\pi^0$ decay. Within the Standard Model, and using flavor-$SU(3)$ relations including first-order breaking corrections, these measurements lead to new predictions with regard to CP violation in $B^+\to J/\psi K^+$ and $B_s\to J/\psi\overline{K}{}^0$ decays, the difference between $S_{\psi K_S}$ and $\sin2\beta$, and the rate and CP asymmetries in $B_s\to J/\psi\pi^0$ decay.

hep-ph↗

arXiv2024

$B_{s}^0\to K^0\overline{K}{}^0$ beyond the Standard Model

Within the Standard Model, the branching fraction of the rare decay $B_s\to K^0\bar K^0$ is related to other decay rates and CP asymmetries through the approximate $SU(3)$ flavor symmetry of the strong interactions and the heavy-quark limit. Three such relations were shown to be violated at a level of about $3\sigma$ each. By means of a systematic search for new-physics explanations of these puzzles, we find that possible solutions are highly fine-tuned and either excluded by other data or rather implausible. The tight correlation between $B_s\to K\bar K$ and $B\to\pi K$ decays, which is maintained even in the presence of flavor-specific new-physics operators, plays a central role in our analysis.

hep-ph↗

arXiv2024

Lessons from ATLAS and CMS measurements of Higgs boson decays to second generation fermions

There is now experimental evidence for Higgs boson decay into a pair of muons, and significant constraints on the Higgs boson decay into a charm quark-antiquark pair. The data on Higgs boson decays into second generation fermions probes various extensions of the Standard Model. We analyze the implications for the Standard Model effective field theory (SMEFT), without and with minimal flavor violation (MFV), for two Higgs doublet models (2HDM) with natural flavor conservation (NFC), for models with vector-like fermions, and for specific models that predict significant modifications of the Yukawa couplings to the light generations.

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arXiv2023

The flavor of a light charged Higgs

The ATLAS Collaboration has recently reported a search for light-charged Higgs in $t\to H^+ b$ decay, with $H^+\to c\bar b$. An excess with a local significance of approximately $3σ$ is found at $m_{H^+}\approx130$ GeV, with a best-fit value of ${\rm BR}(t\to H^+b)\times {\rm BR}(H^+\to c\bar b)=(1.6\pm0.6)\times10^{-3}$. We study the implications of such a hypothetical signal in multi-Higgs doublet models. We take into account constraints from searches for other charged Higgs decays and from flavor-changing neutral current processes. Two Higgs doublet models with flavor structure dictated by natural flavor conservation (NFC), minimal flavor violation (MFV), or the Froggatt-Nielsen (FN) mechanism cannot account for such excess. A three-Higgs doublet model with NFC can account for the signal. The Yukawa couplings of the neutral pseudoscalar $A$ in the down sector, $\hat Y_A^D$, should be larger by a factor of $4-6$ compared to the corresponding Yukawa couplings of the Higgs $h$, $\hat Y_h^D$. We further present two minimal scenarios, one in which a single Yukawa coupling in the down sector, $(\hat Y_A^D)_{bb}$, gives the only significant contribution, and one in which two Yukawa couplings in the up sector, $(\hat Y_A^U)_{tt}$ and $(\hat Y_A^U)_{tc}$, give the only significant contributions, and we discuss possible tests of these scenarios.

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arXiv2023

Time Dependent CP-even and CP-odd Signatures of Scalar Ultra-light Dark Matter in Neutrino Oscillations

Scalar ultra-light dark matter (ULDM) interacting with neutrinos can induce, under certain conditions, time-dependent modifications to neutrino oscillation probabilities. The limit in which the ULDM perturbation can be treated as constant throughout the neutrino propagation time has been addressed by several previous works. We complement these by systematically analyzing the opposite limit -- accounting for the temporal-variations of the ULDM potential by solving time-dependent Schrödinger equations. In particular, we study a novel two-generations-like CP violating (CPV) signature unique to rapidly oscillating ULDM. We derive the leading order, time-dependent, corrections to the oscillation probabilities, both for CP conserving (CPC) and CPV couplings, and explain how they can be measured in current and future experiments.

hep-ph↗

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.

hep-ph↗

arXiv2022

$b\to cτ\barν_{e,μ}$ contributions to $R(D^{(*)})$

The $R(D^{(*)})$ puzzle stands for a $\sim3σ$ violation of lepton flavor universality between the decay rates of $B\to D^{(*)}τν$ and $B\to D^{(*)}\ellν$, where $\ell=e,μ$. If it is accounted for by new physics, there is no reason in general that the relevant neutrinos are, respectively, $ν_τ$ and $ν_\ell$. We study whether the $τ$ related rate could be enhanced by significant contributions to $B\to D^{(*)}τν_\ell$ from a class of operators in the Standard Model Effective Field Theory (SMEFT). We find the upper bounds from forbidden or rare meson decays imply that the contributions from the lepton flavor violating processes account for no more than about $4\%$ of the required shift. Yet, no fine-tuned flavor alignment is required for the new physics. Searching for the related high-$p_T$ process $pp\toτ^\pmμ^\mp$ can at present put a lower bound on the scale of the lepton flavor violating new physics that is a factor of $2.2$ weaker than the bound from meson decays. An exception to our conclusion arises from a specific combination of scalar and tensor SMEFT operators.

hep-ph↗

arXiv2022

Parametric resonance in neutrino oscillations induced by ultra-light dark matter and implications for KamLAND and JUNO

If ultra-light dark matter (ULDM) exists and couples to neutrinos, the neutrino oscillation probability might be significantly altered by a parametric resonance. This resonance can occur if the typical frequency of neutrino flavor-oscillations $Δm^2/(2E)$, where $Δm^2$ is the mass-squared difference of the neutrinos and $E$ is the neutrino energy, matches the oscillation frequency of the ULDM field, determined by its mass, $m_ϕ$. The resonance could lead to observable effects even if the ULDM coupling is very small, and even if its typical oscillation period, given by $τ_ϕ=2π/m_ϕ$, is much shorter than the experimental temporal resolution. Defining a small parameter $ε_ϕ$ to be the ratio between the contribution of the ULDM field to the neutrino mass and the vacuum value of the neutrino mass, the impact of the resonance is particularly significant if $ε_ϕm_ϕL\gtrsim 4$, where $L$ is the distance between the neutrino source and the detector. Such parametric resonance can improve the fit to the KamLAND experiment measurements by about $3.5\,σ$ compared to standard oscillations. This scenario will be tested by the JUNO experiment.

hep-ph↗

arXiv2022

Lessons from the LHCb measurement of CP violation in $B_s\to K^+K^-$

The LHCb experiment measured the time-dependent CP asymmetries $C_{KK}$ and $S_{KK}$ in $B_s\to K^+K^-$ decay. Combining with the corresponding CP asymmetries $C_{ππ}$ and $S_{ππ}$ in $B\to π^+π^-$ decay, we find that the size of $U$-spin breaking in this system is of order $20\%$. Moreover, the data suggest that these effects are dominated by factorizable contributions. We further study the constraints on new physics contributions to $b\to u\bar uq$ ($q=s,d$). New physics that is minimally flavor violating (MFV) cannot be distinguished from the Standard Model (SM) in these decays. However, new physics that is not MFV can mimic large $U$-spin breaking. Requiring that the $U$-spin breaking parameters remain below the size implied by the data leads to a lower bound of $5-10$ TeV on the scale of generic new physics. If the new physics is subject to the selection rules that follow from the Froggatt-Nielsen (FN) mechanism or from General Minimal Flavor Violation (GMFV), the bound is relaxed to 2 TeV.

hep-ph↗

arXiv2021

Probing scalar dark matter oscillations with neutrino oscillations

If ultra-light dark matter (ULDM) exists and couples to neutrinos, it can be discovered via time-periodic variations in the neutrino mass and mixing parameters. We analyze the current bounds on such a scenario and establish the sensitivity expected for both time-averaged and time-resolved modulations in future neutrino oscillation experiments. We place a special emphasis in our analysis on time modulations of the CP violating mixing phase. We illustrate with a toy model the case where the leading modulation effect can be CP violating while the effect on CP conserving parameters is suppressed. We show a unique imprint that a time averaged CP violating modulation of ULDM can leave in neutrino oscillations, while direct CP asymmetries vanish.

hep-ph↗

arXiv2020

The three jewels in the crown of the LHC

The ATLAS and CMS experiments have made three major discoveries: The discovery of an elementary spin-zero particle, the discovery of the mechanism that makes the weak interactions short-range, and the discovery of the mechanism that gives the third generation fermions their masses. I explain how this progress in our understanding of the basic laws of Nature was achieved.

hep-ph↗

arXiv2020

The academic career in physics as a "deal": Choosing physics within a gendered power structure and excellence as an extra hurdle for women

The absence of women among academic staff in physics is in the focus of our research. To explore the causes of this gender imbalance, we conducted a nationwide representative survey among Ph.D. students and interviews with Ph.D. students and postdoctoral fellows. Studying both context factors and agency, we reveal the multiple and hidden ways in which gender operates as a power structure, putting up barriers to women's academic careers. This latent power structure influences women's decision-making and experiences in several ways. In the academic field, it produces unequal competition in a male dominated playground. In the social sphere, choosing a demanding academic career is seen as disrupting gender order. Within the family, women carry a greater burden of family work and give precedence to their partner's career and preferences. Within this social structure, women who decide to follow an academic career feel that they must excel. The demand for excellence acts as an invisible barrier within the gender power structure that prevents talented women from pursuing an academic career in physics.

physics.ed-ph↗

arXiv2020

Analytic Techniques for Solving the Transport Equations in Electroweak Baryogenesis

We develop an efficient method for solving transport equations, particularly in the context of electroweak baryogenesis. It provides fully-analytical results under mild approximations and can also test semi-analytical results, which are applicable in more general cases. Key elements of our method include the reduction of the second-order differential equations to first order, representing the set of coupled equations as a block matrix of the particle densities and their derivatives, identification of zero modes, and block decomposition of the matrix. We apply our method to calculate the baryon asymmetry of the Universe (BAU) in a Standard Model effective field theory framework of complex Yukawa couplings to determine the sensitivity of the resulting BAU to modifications of various model parameters and rates, and to estimate the effect of the commonly-used thin-wall approximation.

hep-ph↗

arXiv2020

Implications of the upper bound on $\boldsymbol{h\toμ^+μ^-}$ on the baryon asymmetry of the Universe

The upper bounds from the ATLAS and CMS experiments on the decay rate of the Higgs boson to two muons provide the strongest constraint on an imaginary part of the muon Yukawa coupling. This bound is more than an order of magnitude stronger than bounds from $\mathcal{CP}$-violating observables, specifically the electric dipole moment of the electron. It excludes a scenario $-$ which had been viable prior to these measurements $-$ that a complex muon Yukawa coupling is the dominant source of the baryon asymmetry. Even with this bound, the muon source can still contribute ${\cal O}(16\%)$ of the asymmetry.

hep-ph↗

arXiv2020

Ph.D. in physics as a hurdle race, and the "glass hurdles" for women

On their way to an academic career in physics, Ph.D. students have to overcome difficulties at many levels. Beyond the intellectual challenge, there are also psychological, social and economic barriers. We studied the difficulties experienced by physics Ph.D. students in the Israeli universities, with special attention to gender-related issues. Among the hurdles that are much more significant for women than for men -- that we call ``the glass hurdles" -- we find gender-related discrimination, sexual harassment, physiological and psychological health issues, and challenges related to pregnancy and parenthood. We make recommendations for ways to confront and remove these barriers in order to provide female physicists with an equal opportunity to succeed.

physics.ed-ph↗

arXiv2020

$CP$ violation from $τ$, $t$ and $b$ dimension-6 Yukawa couplings -- interplay of baryogenesis, EDM and Higgs physics

We explore the implications of the Standard Model effective field theory (SMEFT) with dimension-six terms involving the Higgs boson and third-generation fermion fields on the rate of Higgs boson production and decay into fermions, on the electric dipole moments (EDMs) of the electron, and on the baryon asymmetry of the Universe. We study the consequences of allowing these additional terms for each flavor separately and for combinations of two flavors. We find that a complex $τ$ Yukawa coupling can account for the observed baryon asymmetry $Y_B^{\rm obs}$ within current LHC and EDM bounds. A complex $b$ ($t$) Yukawa coupling can account for $4\%$ ($2\%$) of $Y_B^{\rm obs}$, whereas a combination of the two can reach $12\%$. Combining $τ$ with either $t$ or $b$ enlarges the viable parameter space owing to cancellations in the EDM and in either Higgs production times decay or the total Higgs width, respectively. Interestingly, in such a scenario there exists a region in parameter space where the SMEFT contributions to the electron EDM cancel and collider signal strengths are precisely SM-like, while producing sufficient baryon asymmetry. Measuring $CP$ violation in Higgs decays to $τ$ leptons is the smoking gun for this scenario.

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