Search

Recent progresses in the measurements of the electric dipole moment (EDM) of the electron using the paramagnetic atom or molecule are remarkable. In this paper, we calculate a contribution to the electron EDM at three-loop level, introducing the CP-violating Yukawa couplings of new SU(2)$_L$ multiplets. At two-loop level, the Yukawa interactions generate a CP-violating dimension-six operator, composed of three SU(2)$_L$ field strengths, called the electroweak Weinberg operator. Another one-loop diagram with the operator inserted induces the electron EDM. We find that even if new SU(2)$_L$ particles have masses around TeV-scale, the electron EDM may be larger than the Standard Model contribution to the paramagnetic atom or molecule EDMs. We also discuss the relation between the Barr-Zee diagram contribution at two-loop level and the three-loop one, assuming that the SM Higgs has new Yukawa interactions with the SU(2)$_L$ multiplets., Comment: 21 pages, 6 figures, 2 tables

We present the current situation of the determinations of the first-row CKM components and show the Cabibbo angle anomaly corresponding to a deficit in the first-row CKM unitarity condition at the $3\sigma$ level. In this contribution, we show two new physics interpretations: heavy vector-like quark models and a MeV scale sterile neutrino models. The super tau-charm facility will directly probe the other CKM unitarity conditions related to $V_{cd}$., Comment: Invited contribution to FTCF2024; 15 pages, 5 figures, 1 table

Recently, several new experimental results of the test of lepton flavor universality (LFU) in $B\to D^{(\ast)}$ semi-leptonic decays were announced: the first result of $R_{D}$ from the LHCb Run 1 data, the first results of $R_{D}$ and $R_{D^\ast}$ from the LHCb Run 2 data, and the first result of $R_{D^\ast}$ from the Belle II collaboration. Including these new data, a global analysis still prefers the violation of the LFU between the tau and light leptons. A new world average of the data from the BaBar, LHCb, Belle, and Belle II collaborations is $R_{D} = 0.342 \pm 0.026$ and $R_{D^{\ast}} = 0.287 \pm 0.012$. Including this new data, we update a circumstance of the $b \to c \tau \overline\nu$ measurements and their implications for new physics (NP). Incorporating recent developments for the $B \to D^{(\ast)}$ form factors in the Standard Model (SM), we observe a $4.4 \sigma$ deviation from the SM prediction. Our updates also include; model-independent NP formulae for the related observables; and the global fittings of parameters for leptoquark scenarios as well as single NP operator scenarios. Furthermore, we show future potential to indirectly distinguish different NP scenarios with the use of the precise measurements of the polarization observables in $B\to D^{(\ast)}\tau \overline\nu$ at the Belle II and the high-$p_{\rm T}$ flavored-tail searches at the LHC. We also discuss an impact on the LFU violation in $\Upsilon \to l^+ l^-$., Comment: 48 pages, 5 figures, 6 tables, this paper builds upon an unpublished manuscript arXiv:2210.10751; v2: references added, version accepted for publication in Physical Review D

In this paper, we scrutinize a radiatively generated QCD $\theta$ parameter at the two-loop level based on both full analytical loop functions with the Fock-Schwinger gauge method and the effective field theory approach, using simplified models. We observe that the radiatively generated $\theta$ parameters at the low energy scale precisely match between them. It provides validity to perturbative loop calculations of the QCD $\theta$ parameter with the Fock-Schwinger gauge method. Furthermore, it is also shown that the ordinary Fujikawa method for the radiative $\theta$ parameter by using $\bar\theta = - arg det M_q^{loop}$ does not cover all contributions in the simplified models. But, we also find that when there is a scale hierarchy in $CP$-violating sector, evaluation of the Fujikawa method is numerically sufficient. As an application, we calculate the radiative $\theta$ parameter at the two-loop level in a slightly extended Nelson-Barr model, where the spontaneous $CP$ violation occurs to solve the strong $CP$ problem. It is found a part of the radiative $\theta$ parameters cannot be described by the Fujikawa method., Comment: 24 pages, 4 figures, 1 table; v2: matches version published in JHEP

A modified neutrino sector could imprint a signature on precision measurements of the quark sector because many such measurements rely on the semi-leptonic decays of the charged currents. Currently, global fits of the determinations of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements point to a $3\sigma$-level deficit in the first-row CKM unitarity test, commonly referred to as the Cabibbo-angle anomaly. We find that a MeV sterile neutrino that mixes with the electron-type neutrino increases the extracted $|V_{ud}|$, accommodating the Cabibbo-angle anomaly. This MeV sterile neutrino affects the superallowed nuclear $\beta$ decays and neutron decay, but it barely modifies the other measurements of the CKM elements. While various constraints may apply to such a sterile neutrino, we present viable scenarios within an extension of the inverse seesaw model., Comment: 11 pages, 3 figures; v2: references added; v3: matches version published in PRD

The measurements of the lepton flavor universality (LFU) in $\mathcal{B}({\,\overline{\!B}} \to D^{(\ast)} l \overline{\nu})$ indicate a significant deviation from the standard model prediction at a 3--4 $\sigma$ level, revealing a violation of the LFU ($R_{D^{(\ast)}}$ anomaly). It is known that the $R_{D^{(\ast)}}$ anomaly can be easily accommodated by an $SU(2)_L$-singlet vector leptoquark (LQ) coupled primarily to third-generation fermions, whose existence is further motivated by a partial gauge unification. In general, such a LQ naturally leads to additional $CP$-violating phases in the LQ interactions. In this Letter, we point out that the current $R_{D^{(\ast)}}$ anomaly prefers the $CP$-violating interaction although $\mathcal{B}({\,\overline{\!B}} \to D^{(\ast)} l\overline{\nu})$ are $CP$-conserving observables. The $CP$-violating LQ predicts a substantial size of the bottom-quark electric dipole moment (EDM), the chromo-EDM, and also the tau-lepton EDM. Eventually at low energy, the nucleon and electron EDMs are radiatively induced. Therefore, we conclude that the $R_{D^{(\ast)}}$ anomaly with the $SU(2)_L$-singlet vector LQ provides unique predictions: neutron and proton EDMs with opposite signs and a magnitude of $\mathcal{O}(10^{-27})\,e\,$cm, and suppressed electron EDM. We also show that the similar EDM pattern is predicted in an $SU(2)_L$-doublet scalar LQ scenario. These EDMs could serve as crucial indicators in future experiments., Comment: 12 pages, 8 figures, 1 table; v2: typos in the code fixed, discussion of scalar LQ added, references added

In this article, we review and update implications of the muon anomalous magnetic moment (muon $g-2$) anomaly for two-Higgs-doublet models (2HDMs), which are classified according to imposed symmetries and their resulting Yukawa sector. In the minimal setup, the muon $g-2$ anomaly can be accommodated by the type-X (lepto-philic) 2HDM, flavor-aligned 2HDM (FA2HDM), muon-specific 2HDM ($\mu$2HDM), and $\mu\tau$-flavor violating 2HDM. We summarize all relevant experimental constraints from high-energy collider experiments and flavor experiments, as well as the theoretical constraints from the perturbative unitarity and vacuum stability bounds, to these 2HDMs in light of the muon $g-2$ anomaly. We clarify the available parameter spaces of these 2HDMs and investigate how to probe the remaining parameter regions in future experiments. In particular, we find that, due to the updated $B_s\to\mu^+ \mu^-$ measurement, the remaining parameter region of the FA2HDM is almost equivalent to the one of the type-X 2HDM. Furthermore, based on collider simulations, we find that the type-X 2HDM is excluded and the $\mu$2HDM scenario will be covered with the upcoming Run 3 data., Comment: 46 pages, 9 figures, 2 tables

The two-Higgs-doublet model with a $U(1)_H$ gauge symmetry (N2HDM-$U(1)$) has several advantages compared to the ``standard'' $Z_2$ version (N2HDM-$Z_2$): It is purely based on gauge symmetries, involves only spontaneous symmetry breaking, and is more predictive because it contains one parameter less in the Higgs potential, which further ensures $CP$ conservation, i.e., avoiding the stringent bounds from electric dipole moments. After pointing out that a second, so far unknown version of the N2HDM-$U(1)$ exists, we examine the phenomenological consequences for the Large Hadron Collider (LHC) of the differences in the scalar potentials. In particular, we find that while the N2HDM-$Z_2$ predicts suppressed branching ratios for decays into different Higgs bosons for the case of the small scalar mixing (as suggested by Higgs coupling measurements), both versions of the N2HDM-$U(1)$ allow for sizable rates. This is particularly relevant in light of the CMS excess in resonant Higgs-pair production at around $650\,$GeV of a Standard Model Higgs boson subsequently decaying to photons and a new scalar with a mass of $\approx90\,$GeV subsequently decaying to bottom quarks (i.e., compatible with the CMS and ATLAS $\gamma\gamma$ excesses at $95\,$GeV and $\approx 670\,$GeV). As we will show, this excess can be addressed within the N2HDM-$U(1)$ in case of a nonminimal Yukawa sector, predicting an interesting and unavoidable $Z+ b\bar b$ signal and motivating further asymmetric di-Higgs searches at the LHC., Comment: 11 pages, 2 figures, version accepted in PRD

When the QCD axion is absent in full theory, the strong $CP$ problem has to be explained by an additional mechanism, e.g., the left-right symmetry. Even though tree-level QCD $\bar\theta$ parameter is restricted by the mechanism, radiative corrections to $\bar\theta$ are mostly generated, which leads to a dangerous neutron electric dipole moment (EDM). The ordinary method for calculating the radiative $\bar\theta$ utilizes an equation $\bar \theta= - \text{arg}\, \text{det}\, m_q^{\rm loop}$ based on the chiral rotations of complex quark masses. In this paper, we point out that when full theory includes extra heavy quarks, the ordinary method is unsettled for the extra quark contributions and does not contain its full radiative corrections. We formulate a novel method to calculate the radiative corrections to $\bar\theta$ through a direct loop-diagrammatic approach, which should be more robust than the ordinary one. As an application, we investigate the radiative $\bar\theta$ in the minimal left-right symmetric model. We first confirm a seminal result that two-loop level radiative $\bar\theta$ completely vanishes (corresponding to one-loop corrections to the quark mass matrices). Furthermore, we estimate the size of a non-vanishing radiative $\bar\theta$ at three-loop level. It is found that the resultant induced neutron EDM is comparable to the current experimental bound, and the expected size is restricted by the perturbative unitarity bound in the minimal left-right model., Comment: 32 pages, 5 figures, 2 tables; v2: matches version published in JHEP

There are two tensions related to the Cabibbo angle of the CKM matrix. First, the determinations of $V_{us}$ from $K_{\mu 2}$, $K_{\ell3}$, and $\tau$ decays disagree at the $3\sigma$ level. Second, using the average of these results in combination with $\beta$ decays (including super-allowed $\beta$ decays and neutron decay), a deficit in first-row CKM unitarity with a significance of again about $3\sigma$ is found. These discrepancies, known as the Cabibbo Angle anomaly, can in principle be solved by modifications of $W$ boson couplings to quarks. However, due to $SU(2)_L$ invariance, $Z$ couplings to quarks are also modified and flavour changing neutral currents can occur. In order to consistently assess the agreement of a new physics hypothesis with data, we perform a combined analysis for all dimension-six Standard Model Effective Field Theory operators that generate modified $W$ couplings to first and second generation quarks. We then study models with vector-like quarks, which are prime candidates for a corresponding UV completion as they can affect $W$-quark couplings at tree level, and we perform a global fit including flavour observables (in particular loop effects in $\Delta F=2$ processes). We find that the best fit can be obtained for the $SU(2)_L$ doublet vector-like quark $Q$ as it can generate right-handed $W$-$u$-$d$ and $W$-$u$-$s$ couplings as preferred by data., Comment: 46 pages, 16 figures. v2: Added references, minor numerical changes due to bug in code, conclusions unchanged. v3: journal version, minor clarifications added

Measurements of the branching ratios of $B \to D^{(*)}\tau\bar\nu/B \to D^{(*)}\ell\bar\nu$ and $B_c\to J/\psi\, \tau\bar\nu/B_c\to J/\psi\, \ell\bar\nu$ by the BaBar, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio $\Lambda_b \to\Lambda_c \tau\bar\nu/\Lambda_b \to\Lambda_c \ell\bar\nu$ shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within $2\sigma$ or $1.5\sigma$, depending on the ${\cal R}(\Lambda_c)$ normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results., Comment: 12 pages, 3 tables. Minor corrections, conclusions unchanged, matches journal version

We find that the phase appearing in the unitarity relation between $\mathcal{B}(K_L\rightarrow \mu^+\mu^-)$ and $\mathcal{B}(K_L\rightarrow \gamma\gamma)$ is equal to the phase shift in the interference term of the time-dependent $K\rightarrow \mu^+\mu^-$ 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 $K\rightarrow \mu^+\mu^-$ decay rate to extract the CKM matrix element combination $\vert V_{ts} V_{td} \sin(\beta+\beta_s)\vert\approx A^2\lambda^5\bar\eta$. We find a model-independent theoretically clean prediction, $\cos^2\varphi_0 = 0.96 \pm 0.03$. 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 $\cos\varphi_0$, reducing a four-fold ambiguity in the angle $\varphi_0$ to a two-fold one.

We investigate the di-Higgs production at the Large Hadron Collider in the two-Higgs doublet model (2HDM). In particular, we study the production of an extra neutral Higgs boson $\phi$ in association with the Standard Model (SM) Higgs boson $h$ in the Higgs alignment limit. We analyze two scenarios where the additional Higgs $\phi$ is CP-even or -odd state with a large top-Yukawa interaction. The leading contribution of this production comes from the top-quark loop-induced gluon-fusion channel $gg \to h\phi$. The measurement of the $h\phi$ production can probe the quartic couplings in the Higgs potential as well as the top-Yukawa couplings. Imposing both theoretical constraints (from the perturbative unitarity and the vacuum stability bounds) and experimental bounds (from the SM Higgs and flavor physics measurements) on the 2HDM parameter space, we calculate the production cross-section of $gg \to h\phi$. Furthermore, we scrutinize these processes in the parameter spaces where the CMS di-tau and di-photon excesses around 100$\,$GeV, and/or the muon $g-2$ anomaly can be accommodated., Comment: 26 pages, 5 figures, supplemental material is available in https://www.ttp.kit.edu/preprints/2022/ttp22-061/

Recently, the LHCb collaboration announced a preliminary result of the test of lepton flavor universality (LFU) in $B\to D^{(\ast)}$ semi-leptonic decays: $R_{D}^{\rm LHCb2022} = 0.441 \pm 0.089$ and $R_{D^{\ast}}^{\rm LHCb2022} = 0.281 \pm 0.030$ based on the LHC Run 1 data. This is the first result of $R_{D}$ for the LHCb experiment, and its precision is comparable to the other $B$-factory data. Interestingly, those data prefer the violation of the LFU again. A new world average of the data from the BaBar, Belle, and LHCb collaborations is $R_{D} = 0.358 \pm 0.027$ and $R_{D^{\ast}} = 0.285 \pm 0.013$. Including this new data, we update a circumstance of the $b \to c \tau \overline\nu$ measurements and their implications for new physics. Incorporating recent developments for the $B \to D^{(\ast)}$ form factors in the Standard Model (SM), we observe a $4.1 \sigma$ deviation from the SM predictions. Our updates also include; model-independent new physics (NP) formulae for the related observables; and the global fittings of parameters for leptoquark scenarios as well as single NP operator scenarios. Furthermore, we show future potential to indirectly distinguish different new physics scenarios with the use of the precise measurements of the polarization observables in $B\to D^{(\ast)}\tau \overline\nu$ at the Belle II and the high-$p_{\rm T}$ flavored-tail searches at the LHC. We also discuss an impact on the LFU violation in $\Upsilon \to l^+ l^-$., Comment: 38 pages, 5 figures, 6 Tables; v2: references added; v3: all experimental data are up-to-date, equivalent to arXiv:2405.06062v1; v4: restoring arXiv:2210.10751v2

Fundamental physical constants are determined from a collection of precision measurements of elementary particles, atoms and molecules. This is usually done under the assumption of the Standard Model~(SM) of particle physics. Allowing for light new physics~(NP) beyond the SM modifies the extraction of fundamental physical constants. Consequently, setting NP bounds using these data, and at the same time assuming the CODATA recommended values for the fundamental physical constants, is not reliable. As we show in this Letter, both SM and NP parameters can be simultaneously determined in a consistent way from a global fit. For light vectors with QED-like couplings, such as the dark photon, we provide a prescription that recovers the degeneracy with the photon in the massless limit, and requires calculations only at leading order in the small new physics couplings. At present, the data show tensions partially related to the proton charge radius determination. We show that these can be alleviated by including contributions from a light scalar with flavor non-universal couplings., Comment: 8+16 pages, 3+7 figures, 5 tables

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection., Comment: 108 pages + 38 pages references and appendix, 37 figures, Report of the Topical Group on Beyond the Standard Model Physics at Energy Frontier for Snowmass 2021. The first nine authors are the Conveners, with Contributions from the other authors

The wealth of experimental data collected at laboratory experiments suggests that there is some scale separation between the Standard Model (SM) and phenomena beyond the SM (BSM). New phenomena can manifest itself as small corrections to SM predictions, or as signals in processes where the SM predictions vanish or are exceedingly small. This makes precise calculations of the SM expectations essential, in order to maximize the sensitivity of current and forthcoming experiments to BSM physics. This topical group report highlights some past and forthcoming theory developments critical for maximizing the sensitivity of the experimental program to understanding Nature at the shortest distances., Comment: 36 pages, 2 figures. Report of the TF06 topical group for Snowmass 2021. V2: minor updates

We propose a four-dimensional interpretation of the outgoing state of the scattering of a massless fermion off a Dirac monopole. It has been known that such a state has fractional fermion numbers and is necessarily outside the Fock space on top of ordinary perturbative vacuum, when more than two flavours of charged Dirac fermions are considered. In this paper, we point out that the Fock space of the fermions depends on the rotor degree of freedom of the monopole and changes by a monopole-fermion s-wave scattering. By uplifting the fermion-rotor system introduced by Polchinski, from two to four dimensions, we argue that the outgoing state can be understood as a state in a different Fock space., Comment: 28 pages, 2 figures, 1 table; v2: references added, matches version published in JHEP

Recently, the CMS collaboration has reported a di-tau excess with a local significance of 2.6-3.1$\sigma$ where the invariant mass is $m_{\tau\tau}=$95-100 GeV. This excess can be interpreted as a light scalar boson that couples to the third generation fermions, particularly top and $\tau$. Based on the simplest model that can account for the CMS di-tau excess, we evaluate experimental sensitivities to the additional light resonance, using the results reported by the ATLAS collaboration. We see that a search for the top-quark associated production of the SM Higgs boson that decays into $\tau\bar\tau$ sets a strong model-independent limit. We also find that the CP-even scalar interpretation of the light resonance is excluded by the ATLAS results, while the CP-odd interpretation is not., Comment: 20 pages, 3 figures, 1 table; v2: references added; v3: matches version published in EPJC

The rare flavour changing top quark decay $t\to cZ$ is a clear sign of new physics and experimentally very interesting due to the huge number of top quarks produced at the LHC. However, there are few (viable) models which can generate a sizable branching ratio for $t\to cZ$ -- in fact vector-like quarks seem to be the only realistic option. In this paper, we investigate all three representations (under the Standard Model gauge group) of vector-like quarks ($U$, $Q_1$ and $Q_7$) that can generate a sizable branching ratio for $t\to cZ$ without violating bounds from $B$ physics. Importantly, these are exactly the three vector-like quarks which can lead to a sizable positive shift in the prediction for $W$ mass, via the couplings to the top quark also needed for a sizable Br($t\to cZ$). Calculating and using the one-loop matching of vector-like quarks on the Standard Model Effective Field Theory, we find that Br($t\to cZ$) can be of the order of $10^{-6}$, $10^{-5}$ and $10^{-4}$ for $U$, $Q_1$ and $Q_7$, respectively and that in all three cases the large $W$ mass measurement can be accommodated., Comment: 8 pages, 2 figures + supplemental material. v2: Accepted to PRD, discussion of future lepton colliders added, units corrected in eq II.9, further references added

Once all the sleptons as well as the Bino are observed at the ILC, the Bino contribution to the muon anomalous magnetic dipole moment (muon $g-2$) in supersymmetric (SUSY) models can be reconstructed. Motivated by the recently confirmed muon $g-2$ anomaly, we examine the reconstruction accuracy at the ILC with $\sqrt{s}$ = 500 GeV. For this purpose, measurements of stau parameters are important. We quantitatively study the determination of the mass and mixing parameters of the staus at the ILC. Furthermore, we discuss the implication of the stau study to the reconstruction of the SUSY contribution to the muon $g-2$. At the benchmark point of our choice, we find that the SUSY contribution to the muon $g-2$ can be determined with a precision of $\sim 1\%$ at the ILC., Comment: 19 pages, 5 figures, contribution to Snowmass 2021

The International Linear Collider (ILC) is on the table now as a new global energy-frontier accelerator laboratory taking data in the 2030s. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community., Comment: 356 pages, Large pdf file (40 MB) submitted to Snowmass 2021; v2 references to Snowmass contributions added, additional authors; v3 references added, some updates, additional authors

In this contribution to the Snowmass 2021 process we review theoretical developments in the Standard Model Effective Field Theory (SMEFT) with a focus on effects at the dimension-8 level and beyond. We review the theoretical advances that led to the complete construction of the operator bases for the dimension-8 and dimension-9 SMEFT Lagrangians. We discuss the possibility of obtaining all-orders results in the $1/\Lambda$ expansion for certain SMEFT observables as well as the current status of renormalization group running and implications for positivity, and briefly present the on-shell approach to constructing SMEFT amplitudes. Finally we present several new phenomenological effects that first arise at dimension-8 and discuss the impact of these terms on experimental analyses., Comment: 37 pages, 6 figures; contribution to Snowmass 2021; new section and additional authors

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., Comment: 108 pages, 25 figures, 9 tables, matches the published version

We study the on-shell version of the Higgs mechanism in effective theories (EFTs) containing particles of different spins, focusing on contact terms as a simple starting point. We derive the massive contact terms and their coefficients from the massless amplitudes of the EFT above the symmetry breaking scale, by covariantizing the massless contact terms under the massive little group. In the little-group-covariant massive-spinor formalism, this notationally amounts to bolding spinor labels. Mass-suppressed contributions to the contact-term coefficients arise from higher-point contact terms with additional soft Higgs legs. We apply this procedure to obtain massive four-point amplitudes featuring scalars, spin 1/2 fermions and vectors, in the standard-model EFT. The subleading helicity-flipped components of each massive contact term, which are dictated by little-group covariance, are associated with the residues of factorizable massless amplitudes. Extra "frozen" Higgses emitted from each leg of a massless contact term supply the additional light-like momentum component, needed to form a massive leg of the same polarization. As another application, we derive various components of massive three-point amplitudes from massless amplitudes with up to three additional Higgses, in a standard-model-like toy model., Comment: 29 pages, 6 figures, 4 appendices

Motivated by the $b \to c \tau \overline{\nu}$ anomalies, we study non-resonant searches for new physics at the large hadron collider (LHC) by considering final states with an energetic and hadronically decaying $\tau$ lepton, a $b$-jet and large missing transverse momentum ($pp \to \tau_h \overline{b} + E_{\rm T}^{\rm miss}$). Such searches can be useful to probe new physics contributions to $b \to c \tau \overline{\nu}$. They are analyzed not only within the dimension-six effective field theory (EFT) but also in explicit leptoquark (LQ) models with the LQ non-decoupled. The former is realized by taking a limit of large LQ mass in the latter. It is clarified that the LHC sensitivity is sensitive to the LQ mass for $O(1)$ TeV even in the search of $pp \to \tau_h \overline{b} + E_{\rm T}^{\rm miss}$. Although the LQ models provide a weaker sensitivity than the EFT limit, it is found that the non-resonant search of $pp \to \tau_h \overline{b} + E_{\rm T}^{\rm miss}$ can improve the sensitivity by $\approx 40\%$ versus a conventional mono-$\tau$ search ($pp \to \tau_h + E_{\rm T}^{\rm miss}$) in the whole LQ mass region. Consequently, it is expected that most of the parameter regions suggested by the $b \to c \tau \overline{\nu}$ anomalies can be probed at the HL-LHC. Also, it is shown that $\text{R}_2$ LQ scenario is accessible entirely once the LHC Run 2 data are analyzed. In addition, we discuss a charge selection of $\tau_h$ to further suppress the standard-model background, and investigate the angular correlations among $b,\, \tau$ and the missing transverse momentum to discriminate the LQ scenarios., Comment: 39 pages, 9 figures, 14 tables. Ancillary files are available, JHEP published version

The Fermilab Muon $g-2$ collaboration recently announced the first result of measurement of the muon anomalous magnetic moment ($g-2$), which confirmed the previous result at the Brookhaven National Laboratory and thus the discrepancy with its Standard Model prediction. We revisit low-scale supersymmetric models that are naturally capable to solve the muon $g-2$ anomaly, focusing on two distinct scenarios: chargino-contribution dominated and pure-bino-contribution dominated scenarios. It is shown that the slepton pair-production searches have excluded broad parameter spaces for both two scenarios, but they are not closed yet. For the chargino-dominated scenario, the models with $m_{\tilde{\mu}_{\rm L}}\gtrsim m_{\tilde{\chi}^{\pm}_1}$ are still widely allowed. For the bino-dominated scenario, we find that, although slightly non-trivial, the region with low $\tan \beta$ with heavy higgsinos is preferred. In the case of universal slepton masses, the low mass regions with $m_{\tilde{\mu}}\lesssim 230$ GeV can explain the $g-2$ anomaly while satisfying the LHC constraints. Furthermore, we checked that the stau-bino coannihilation works properly to realize the bino thermal relic dark matter. We also investigate heavy staus case for the bino-dominated scenario, where the parameter region that can explain the muon $g-2$ anomaly is stretched to $m_{\tilde{\mu}}\lesssim 1.3$ TeV., Comment: 26 pages, 4 figures, 2 tables; v2: references added; v3: version published in JHEP

The purely on-shell approach to effective field theories requires the construction of independent contact terms. Employing the little-group-covariant massive-spinor formalism, we present the first systematic derivation of independent four-point contact terms involving massive scalars, spin-1/2 fermions, and vectors. Independent three-point amplitudes are also listed for massive particles up to spin-3. We make extensive use of the simple relations between massless and massive amplitudes in this formalism. Our general results are specialized to the (broken-phase) particle content of the electroweak sector of the standard model. The (anti)symmetrization among identical particles is then accounted for. This work opens the way for the on-shell computation of massive four-point amplitudes., Comment: 27 pages, 1 figure and 5 tables; v2: vvvs counting corrected

Recently, the standard model predictions for the $B$-meson hadronic decays, $\bar{B}^0 \to D^{(\ast)+}K^-$ and $\bar{B}^0_s \to D^{(\ast)+}_s \pi^-$, have been updated based on the QCD factorization approach. This improvement sheds light on a novel puzzle in the $B$-meson hadronic decays: there are mild but universal tensions between data and the predicted branching ratios. Assuming the higher-order QCD corrections are not huge enough to solve the tension, we examine several new physics interpretations of this puzzle. We find that the tension can be partially explained by a left-handed $W^\prime$ model, which can be compatible with other flavor observables and collider bounds., Comment: 9 pages, 1 figure; v2: references added; v3: version published as a Rapid Communication in PRD

We propose a novel approach in a search for the neutron electric dipole moment (EDM) by taking advantage of signal amplification in a weak measurement, known as weak value amplification. Considering an analogy to the weak measurement that can measure the spin magnetic moment interaction, we examine an experimental setup with a polarized neutron beam through an external electric field with spatial gradient, where the signal is sensitive to the EDM interaction. In particular, a dedicated analysis of effects from impurities in pre- and post-selections is performed. We show that the weak value amplification occurs where the signal is enhanced by up to two orders of magnitude, and demonstrate a potential sensitivity of the proposed setup to the neutron EDM., Comment: 16 pages, 4 figures; v3: several minor modifications, references added, published version

Recently, it was pointed out that the electron and muon g-2 discrepancies can be explained simultaneously by a flavor-violating axion-like particle (ALP). We show that the parameter regions favored by the muon g-2 are already excluded by the muonium-antimuonium oscillation bound. In contrast, those for the electron g-2 can be consistent with this bound when the ALP is heavier than 1.5 GeV. We propose to search for a signature of the same-sign and same-flavor lepton pairs and the forward-backward muon asymmetry to test the model at the Belle II experiment., Comment: 22 pages, 5 figures, JHEP version

Supersymmetric models with sub-TeV charginos and sleptons have been a candidate for the origin of the long-standing discrepancy in the muon anomalous magnetic moment (g-2). By gathering all the available LHC Run 2 results, we investigate the latest LHC constraints on models that explain the anomaly by their chargino contribution to the muon g-2. It is shown that the parameter regions where sleptons are lighter than charginos are strongly disfavored. In contrast, we find that the models with $m_{\tilde{\mu}_{\mathrm L}}\gtrsim m_{{\tilde\chi}^{\pm}_1}$ are still widely allowed, where the lighter chargino dominantly decays into a W-boson and a neutralino., Comment: 35 pages, 14 figures; 2021 Spring Update with the latest LHC and g-2 data

The KOTO experiment recently reported four candidate events in the signal region of $K_L\to \pi^0 \nu\bar\nu$ search, where the standard model only expects $0.10\pm 0.02$ events. If confirmed, this requires physics beyond the standard model to enhance the signal. We examine various new physics interpretations of the result including these: (1) heavy new physics boosting the standard model signal, (2) reinterpretation of "$\nu\bar{\nu}$" as a new light long-lived particle, or (3) reinterpretation of the whole signal as the production of a new light long-lived particle at the fixed target. We study the above explanations in the context of a generalized new physics Grossman-Nir bound coming from the $K^+ \to \pi^+\nu\bar{\nu}$ decay, bounded by data from the E949 and the NA62 experiments., Comment: 7 pages, 3 figures; v2: references added, simulation refined; v3: matches version published in PRL

We apply on-shell methods to the bottom-up construction of electroweak amplitudes, allowing for both renormalizable and non-renormalizable interactions. We use the little-group covariant massive-spinor formalism, and flesh out some of its details along the way. Thanks to the compact form of the resulting amplitudes, many of their properties, and in particular the constraints of perturbative unitarity, are easily seen in this formalism. Our approach is purely bottom-up, assuming just the standard-model electroweak spectrum as well as the conservation of electric charge and fermion number. The most general massive three-point amplitudes consistent with these symmetries are derived and studied in detail, as the primary building blocks for the construction of scattering amplitudes. We employ a simple argument, based on tree-level unitarity of four-point amplitudes, to identify the three-point amplitudes that are non-renormalizable at tree level. This bottom-up analysis remarkably reproduces many low-energy relations implied by electroweak symmetry through the standard-model Higgs mechanism and beyond it. We then discuss four-point amplitudes. The gluing of three-point amplitudes into four-point amplitudes in the massive spinor helicity formalism is clarified. As an example, we work out the $\psi^c \psi Zh$ amplitude, including also the non-factorizable part. The latter is an all-order expression in the effective-field-theory expansion. Further constraints on the couplings are obtained by requiring perturbative unitarity. In the $\psi^c \psi Zh$ example, one for instance obtains the renormalizable-level relations between vector and fermion masses and gauge and Yukawa couplings. We supplement our bottom-up derivations with a matching of three- and four-point amplitude coefficients onto the standard-model effective field theory (SMEFT) in the broken electroweak phase., Comment: 55 pages, 2 figures, references added, journal version

In this addendum to arXiv:1811.09603 we update our results including the recent measurement of ${\cal R}(D)$ and ${\cal R}(D^*)$ by the Belle collaboration: ${\cal R}(D)_{\rm Belle} = 0.307\pm0.037\pm0.016$ and ${\cal R}(D^*)_{\rm Belle}=0.283\pm0.018\pm0.014$, resulting in the new HFLAV fit result ${\cal R}(D) = {0.340\pm0.027 \pm 0.013}$, ${\cal R}(D^*) = {0.295\pm0.011 \pm 0.008 }$, exhibiting a $3.1\,\sigma$ tension with the Standard Model. We present the new fit results and update all figures, including the relevant new collider constraints. The updated prediction for ${\cal R}(\Lambda_c)$ from our sum rule reads ${\cal R}(\Lambda_c)= \mathcal{R}_{\rm SM}(\Lambda_c) \left( 1.15 \pm 0.04 \right) = 0.38 \pm 0.01 \pm 0.01$. We also comment on theoretical predictions for the fragmentation function $f_c$ of $b\to B_c$ and their implication on the constraint from $B_{u/c}\to\tau\nu$ data., Comment: 9 pages, 7 figures. v2: references added, matches PRD version

The combined analysis of the BaBar, Belle, and LHCb data on $B\to D\tau\nu$, $B\to D^*\tau\nu$ and $B_c\to J/\Psi\tau\nu$ decay observables shows evidence of physics beyond the Standard Model (SM). In this article, we study all the one- and two-dimensional scenarios which can be generated by adding a single new particle to the SM. We put special emphasis on the model-discriminating power of $F_L(D^*)$ and of the $\tau$ polarizations, and especially on the constraint from the branching fraction ${\rm BR}(B_c\to\tau\nu)$. We critically review this constraint and do not support the aggressive limit of ${\rm BR}(B_c\to\tau\nu)<10\%$ used in some analyses. While the impact of $F_L(D^*)$ is currently still limited, the ${\rm BR}(B_c\to\tau\nu)$ constraint has a significant impact: depending on whether one uses a limit of $60\%$, $30\%$ or $10\%$, the pull for new physics (NP) in scalar operators changes drastically. More specifically, for a conservative $60\%$ limit a scenario with scalar operators gives the best fit to data, while for an aggressive $10\%$ limit this scenario is strongly disfavored and the best fit is obtained in a scenario in which only a left-handed vector operator is generated. We find a sum rule for the branching ratios of $B\to D\tau\nu$, $B\to D^*\tau\nu$ and $\Lambda_b\to \Lambda_c\tau\nu$ which holds for any NP contribution to the Wilson coefficients. This sum rule entails an enhancement of ${\rm BR}(\Lambda_b\to \Lambda_c\tau\nu)$ over its SM prediction by $(24\pm 6)\%$ for the current $\mathcal{R}(D^{(*)})$ data., Comment: 16 pages, 6 figures; v2: clarifying comments and few references added, matches version published in PRD; v3: typo corrected in eq. (28). Updated results based on the HFLAV average for spring 2019 are available in arXiv:1905.08253

Polarization measurements in $\bar{B} \to D^{(\ast)} \tau \overline{\nu}$ are useful to check consistency in new physics explanations for the $R_{D}$ and $R_{D^{\ast}}$ anomalies. In this paper, we investigate the $D^{\ast}$ and $\tau$ polarizations and focus on the new physics contributions to the fraction of a longitudinal $D^{\ast}$ polarization ($F_{L}^{D^{\ast}}$), which is recently measured by the Belle collaboration $F_{L}^{D^{\ast}} = 0.60 \pm 0.09$, in model-independent manner and in each single leptoquark model (${\rm R}_2$, ${\rm S}_1$ and ${\rm U}_1$) that can naturally explain the $R_{D^{(\ast)}}$ anomalies. It is found that $\mathcal{B}(B_c^{+} \to \tau^{+} \nu)$ severely restricts deviation from the Standard Model (SM) prediction of $F_{L, \textrm{SM}}^{D^{\ast}} = 0.46 \pm 0.04$ in the leptoquark models: [0.43, 0.44], [0.42, 0.48], and [0.43, 0.47] are predicted as a range of $F_{L}^{D^{\ast}}$ for the ${\rm R}_2$, ${\rm S}_1$, and ${\rm U}_1$ leptoquark models, respectively, where the current data of $R_{D^{(\ast)}}$ is satisfied at $1\,\sigma$ level. It is also shown that the $\tau$ polarization observables can much deviate from the SM predictions. The Belle II experiment, therefore, can check such correlations between $R_{D^{(\ast)}}$ and the polarization observables, and discriminate among the leptoquark models., Comment: 24 pages, 3 figures, 1 table; references added, version published in JHEP

We investigate model independent top-quark corrections to $\Delta F = 2$ processes for the down-type quarks within the framework of the Standard Model Effective Field Theory. Dimension-six $\Delta F = 1$ operators contribute to them through renormalization group evolutions and matching conditions. We provide a complete one-loop matching formula from the top quarks for $\Delta F=2$ transitions. We also demonstrate these corrections on $\Delta M_{B_s}$ in the left-right symmetric model, which are compared with the conventional calculation., Comment: 30 pages, 5 figures; version published in JHEP

The first lattice result from the RBC and UKQCD Collaborations and improved perturbative calculations of $\varepsilon^{\prime}_K / \varepsilon_K$ have implied that the Standard-Model (SM) expectation deviates from measured values at the $2.8\,\sigma$ level. Since $\varepsilon^{\prime}_K / \varepsilon_K$ comes from $CP$-violating FCNC and is significantly suppressed in the SM, the discrepancy can be explained easily in several new physics (NP) models. In this contribution, it is shown that correlations with the other rare decays, especially $K\to \pi \nu \overline{\nu}$ and $K_S \to \mu^+ \mu^-$, are crucial for discrimination of the NP models. These channels can be probed precisely in the future by the NA62 and KOTO experiments for $K\to \pi \nu \overline{\nu}$ and LHCb experiment for $K_S \to \mu^+ \mu^-$., Comment: 8 pages, 3 figures; Contribution to proceedings of XIV International Conference on Heavy Quarks and Leptons (HQL2018), Yamagata Terrsa, Japan, May 27- June 1, 2018. arXiv admin note: text overlap with arXiv:1705.05462

We evaluate long-distance electromagnetic (QED) contributions to $\bar{B}{}^0 \to D^+ \tau^{-} \bar{\nu}_{\tau}$ and $B^- \to D^0 \tau^{-} \bar{\nu}_{\tau}$ relative to $\bar{B}{}^0 \to D^+ \mu^{-} \bar{\nu}_{\mu}$ and $B^- \to D^0 \mu^{-} \bar{\nu}_{\mu}$, respectively, in the standard model. We point out that the QED corrections to the ratios $R(D^{+})$ and $R(D^{0})$ are not negligible, contrary to the expectation that radiative corrections are almost canceled out in the ratio of the two branching fractions. The reason is that long-distance QED corrections depend on the masses and relative velocities of the daughter particles. We find that theoretical predictions for $R(D^{+})^{\tau/\mu}$ and $R(D^{0})^{\tau/\mu}$ can be amplified by $\sim4\%$ and $\sim3\%$, respectively, for the soft-photon energy cut in range $20$-$40$ MeV., Comment: 5 pages, 3 figures; v3: several minor modifications, references added, published version

In light of a discrepancy of the direct $CP$ violation in $K\to\pi\pi$ decays, $\varepsilon'/\varepsilon_K$, we investigate gluino contributions to the electroweak penguin, where flavor violations are induced by squark trilinear couplings. Top-Yukawa contributions to $\Delta S = 2$ observables are taken into account, and vacuum stability conditions are evaluated in detail. It is found that this scenario can explain the discrepancy of $\varepsilon'/\varepsilon_K$ for the squark mass smaller than 5.6 TeV. We also show that the gluino contributions can amplify $\mathcal{B}(K \to \pi \nu \overline{\nu})$, $\mathcal{B}(K_S \to \mu^+ \mu^-)_{\rm eff}$ and $\Delta A_{\rm CP}(b\to s\gamma)$. Such large effects could be measured in future experiments., Comment: 30 pages, 8 figures; references added, version published in JHEP

We explore supersymmetric contributions to the decay $K_S^0\rightarrow\mu^+\mu^-$, in light of current experimental data. The Standard Model (SM) predicts $\mathcal{B}(K_S^0\rightarrow\mu^+\mu^-)\approx5\times 10^{-12}$. We find that contributions arising from flavour violating Higgs penguins can enhance the branching fraction up to $\approx 35\times 10^{-12}$ within different scenarios of the Minimal Supersymmetric Standard Model (MSSM), as well as suppress it down to $\approx 0.78\times 10^{-12}$. Regions with fine-tuned parameters can bring the branching fraction up to the current experimental upper bound, $8\times 10^{-10}$. The mass degeneracy of the heavy Higgs bosons in MSSM induces correlations between $\mathcal{B}(K_S^0\rightarrow\mu^+\mu^-)$ and $\mathcal{B}(K_L^0\rightarrow\mu^+\mu^-)$. Predictions for the $CP$ asymmetry in $K^0\rightarrow\mu^+\mu^-$ decays in the context of MSSM are also given, and can be up to eight times bigger than in the SM., Comment: 36 pages, 31 figs

A rare decay $K_L \to \mu^+ \mu^- $ has been measured precisely, while a rare decay $K_S \to \mu^+ \mu^- $ will be observed by an upgrade of the LHCb experiment. Although both processes are almost CP-conserving decays, we point out that an interference contribution between $K_L$ and $K_S$ in the kaon beam emerges from a genuine direct CP violation. It is found that the interference contribution can change $K_S \to \mu^+ \mu^-$ standard-model predictions at $\mathcal{O}(60\%)$. We also stress that an unknown sign of $\mathcal{A}(K_L \to \gamma \gamma)$ can be determined by a measurement of the interference, which can much reduce a theoretical uncertainty of $\mathcal{B}(K_L \to \mu^+ \mu^-)$. We also investigate the interference in a new physics model, where the $\epsilon'_K / \epsilon_K$ tension is explained by an additional $Z$-penguin contribution., Comment: 6 pages, 2 figures; references added, version published in PRL

Recent calculations have pointed to a 2.8 $\sigma$ tension between data on $\epsilon^{\prime}_K / \epsilon_K$ and the standard-model (SM) prediction. Several new physics (NP) models can explain this discrepancy, and such NP models are likely to predict deviations of $\mathcal{B}(K\to \pi \nu \overline{\nu})$ from the SM predictions, which can be probed precisely in the near future by NA62 and KOTO experiments. We present correlations between $\epsilon^{\prime}_K / \epsilon_K$ and $\mathcal{B}(K\to \pi \nu \overline{\nu})$ in two types of NP scenarios: a box dominated scenario and a $Z$-penguin dominated one. It is shown that different correlations are predicted and the future precision measurements of $K \to \pi \nu \overline{\nu}$ can distinguish both scenarios., Comment: 4 pages, 2 figures; Contribution to proceedings of 52th Rencontres de Moriond electroweak interactions and unified theories, La Thuile, Italy, 18-25 March, 2017; references added

The Standard-Model (SM) prediction for the CP-violating quantity $\epsilon_K^{\prime}/\epsilon_K$ deviates from its measured value by 2.8 $\sigma$. It has been shown that this tension can be resolved within the Minimal Supersymmetric Standard Model (MSSM) through gluino-squark box diagrams, even if squarks and gluinos are much heavier than 1 TeV. The rare decays $K_L \to \pi^0\nu\bar{\nu}$ and $K^+ \to \pi^+\nu\bar{\nu}$ are similarly sensitive to very high mass scales and the first one also measures CP violation. In this article, we analyze the correlations between $\epsilon^{\prime}_K/\epsilon_K$ and $B(K_L \to \pi^0\nu\bar{\nu})$ and $B(K^+ \to \pi^+\nu\bar{\nu})$ within the MSSM aiming at an explanation of $\epsilon_K^{\prime}/\epsilon_K$ via gluino-squark box diagrams. The dominant MSSM contribution to the $K \to \pi\nu\bar{\nu}$ branching fractions stems from box diagrams with squarks, sleptons, charginos, and neutralinos, and the pattern of the correlations is different from the widely studied $Z$-penguin scenarios. This is interesting in light of future precision measurements by KOTO and NA62 at J-PARC and CERN, respectively. We find $B(K_L \to \pi^0\nu\bar{\nu})/B^{SM} (K_L \to \pi^0\nu\bar{\nu})\lesssim 2\,(1.2)$ and $B(K^+ \to \pi^+\nu\bar{\nu})/B^{SM}(K^+ \to \pi^+\nu\bar{\nu}) \lesssim 1.4\,(1.1)$, if all squark masses are above 1.5 TeV, gaugino masses obey GUT relations, and if one allows for a fine-tuning at the $1\%\,(10\%)$ level for the gluino mass. Larger values are possible for a tuned CP violating phase. Furthermore, the sign of the MSSM contribution to $\epsilon_K^{\prime}$ imposes a strict correlation between $B(K_L \to \pi^0\nu\bar{\nu})$ and the hierarchy between the masses $m_{\bar{U}}$, $m_{\bar{D}}$ of the right-handed up-squark and down-squark: sgn$[B(K_L \to \pi^0\nu\bar{\nu})-B^{SM} (K_L \to \pi^0\nu\bar{\nu})] = $sgn$(m_{\bar{U}}-m_{\bar{D}}) $., Comment: 9 pages, 5 figures; references added, version published in PRD

New physics contributions to the $Z$ penguin are revisited in the light of the recently-reported discrepancy of the direct CP violation in $K\to\pi\pi$. Interference effects between the standard model and new physics contributions to $\Delta S = 2$ observables are taken into account. Although the effects are overlooked in the literature, they make experimental bounds significantly severer. It is shown that the new physics contributions must be tuned to enhance $\mathcal{B}(K_L \to \pi^{0} \nu \bar{\nu})$, if the discrepancy of the direct CP violation is explained with satisfying the experimental constraints. The branching ratio can be as large as $6 \times 10^{-10}$ when the contributions are tuned at the 10 % level., Comment: 18 pages, 6 figures; v2: references added, some contributions included in light of gauge invariance; v3: to be published in Phys. Lett. B