Abstract

The detection of primordial gravitational waves would offer a direct evidence of inflation and valuable insights into the dynamics of the early Universe. During postinflation reheating period, when the inflaton coherently oscillates at the bottom of its potential, primordial stochastic gravitational waves may be sourced by its perturbative decay into particles of different spins. Assuming the behavior of the potential near the minimum as a polynomial 𝑉⁡(𝜙) ∼𝜙^𝑘, where 𝑘 ≥2, and treating the inflaton as coherently oscillating classical field, we calculate the decay of inflaton into a pair of spin 3/2 particles accompanied by graviton emission. We numerically study the reheating dynamics and calculate the stochastic gravitational wave spectra. Our analysis shows that the gravitational wave spectra can offer insights into the microscopic physics during inflation.

Abstract

This study investigates TeV-scale vector leptoquarks (vLQs) and their contributions to the magnetic dipole moments of charged leptons. Significant parameter space for these LQs is excluded using current LHC data. Among vLQs only U1 and V2 can account for the observed positive shift in (a^mu_exp-a^mu_SM) through a lepton chirality-flipping contribution with
LQ-quark-lepton coupling. These LQs can also fits for the electron dipole moment and atomic-parity violation measurements.

Abstract

The combined Planck, BICEP/Keck Array and BAO measurements of the scalar spectral indexand the tensor-to-scalar ratio from the cosmic microwave background observations severely constrain orcompletely rule out several models of inflationary potentials. On the other hand, the data seems to favorconcave potentials over convex ones. In this paper, we study preheating and gravitational waves after infla-tion in a large-field, regularized hilltop potential where inflation takes place in the concave plateau. Theinflaton, φ, is coupled to a subdominant scalar field, χ, through a quartic coupling. After inflation ends, φoscillates about the potential minimum and becomes inhomogeneous. The growth of the fluctuation modes,δφkand δχk, on a homogeneous oscillating background is analyzed in linear perturbation theory, revealingthat small modes likely experience broad self-resonance or external parametric resonance. To determine ifthe resonances are sufficiently strong to cause unstable growth of the modes we perform a lattice simula-tion. The lattice simulations demonstrate that, although the initial i nhomogeneities generate a stochasticgravitational wave background that remains below the present observational limit, the fluctuations do notgrow exponentially, and the occupation numbers of δφkand δχkremain close to zero.

Abstract

The Belle II experiment has recently reported the first measurement of B+→K+vvˉ decay which exceeds the Standard Model prediction by approximately 2.7σ. The deviation may indicate the presence of new physics beyond the Standard Model in the b→svvˉsector. Under this assumption, we study the hadronic Λb→Λ(→pπ)vvˉ and Λb→Λ⋆(→NKˉ)vvˉ decays within both the Standard Model and beyond. We work in a low-energy effective field theory framework with additional light right-handed neutrinos. We calculate the differential branching ratios of these decay modes and explore the implications of the Belle II results through various observables.

Abstract

Leptoquarks (LQs) can contribute to the magnetic and electric dipole moments of charged leptons, which the current experiments have measured with good accuracy. We revisit the parameter spaces of TeV-scale vector LQs that contribute to these observables and study how these models fare against the LHC bounds. We show that significant portions of the parameter space are excluded when the current LHC data is utilized effectively. We find that only U1and V2 can explain the observed positive shift in (aμexp-aμSM) through a lepton chirality-flipping contribution with
O(1) LQ-quark-lepton coupling. We also see how these two LQs can fit the electron dipole moment and atomic parity violation measurements. We find that the current electric dipole moment measurements of the muon cannot restrain the LQ-quark-lepton couplings within perturbative regions.

Abstract

We investigate the possible sizes of all the CP-violating asymmetries offered by the angular distribution of rare decay Λb → Λð→ pπ−Þlþl− in the Standard Model and new physics scenarios motivated by the recent b → slþl− anomalies. We work in a model-independent effective theory framework and discuss the sensitivity of CP asymmetries to new O9;10 operators and their chirality flipped counterparts. We find that the size of many of the CP asymmetries can be at the level of a few percent in new physics scenarios consistent with current b → slþl− data at a level of 1σ. We emphasize that measurements of these CP asymmetries can be used to discriminate different new physics scenarios in b → slþl−.

Abstract

Abstract: We calculate QED corrections to the semileptonic decays H1 → H2ℓ +ℓ − where ℓ = e, µ and H1,2 are hadrons. The soft and/or collinear divergences are regulated in a gauge-invariant manner and demonstrably cancel, leaving behind a finite residue that depends on the (infrared) momentum cutoff below which a photon is considered to be indistinguishable. On resuming, the said sensitivity reduces drastically, i.e., for the NLL result as compared to the NLO one. The overall correction is negative and its magnitude is larger for a lighter lepton. For B → K(∗) decays, the corrections improve the agreement for the differential distributions, while the behavior is more complicated for Λb → Λ (∗) decays. Rather intriguingly, the corrections serve to regenerate the tension for the lepton flavor universality observables RK and RK∗ .

Abstract

We study lepton number violating and lepton number conserving semileptonic decays of heavy baryons Λ0 b to three charged leptons and a neutrino. The decays occur through two intermediate quasidegenerate GeV-scale sterile neutrinos of either Majorana or Dirac type that can be on-shell. Interference between the intermediate heavy neutrinos leads to CP violation in the final states. Effect of neutrino oscillations between the heavy states are also considered in observables of interests, i.e., branching ratio, and the CP-asymmetry. Given the present constraints on the heavy-to-light mixing elements jVeNj and jVμNj, CP-averaged branching ratio of Λ0 b → ðΛc; pÞμμeν with intermediate Majorana neutrinos is almost two orders of magnitude larger than for the same with Dirac neutrinos, whereas, CP-averaged branching ratio of Λ0 b → ðΛc; pÞeeμν is of the same order of magnitude for both Majorana and Dirac neutrino induced decays. CP-violation is found to be appreciable when the neutrino mass difference is comparable with the average decay widths.

Abstract

We investigate the possible sizes of all the CP-violating asymmetries offered by the angular distribution of rare decay Λb → Λ(→ pπ−)` +` − in the Standard Model and new physics scenarios motivated by the recent b → s`+` − anomalies. We work in a model-independent effective theory framework and discuss the sensitivity of CP asymmetries to new O9,10 operators and their chirality flipped counterparts. We find that the size of many of the CP asymmetries can be at the level of few percent in new physics scenarios consistent with current b → s`+` − data at level of 1σ. We emphasize that measurements of these CP asymmetries can be used to discriminate different new physics scenarios in b → s`+` −.

Abstract

We determine the strange quark mass ( � � ) and quark mixing element | � � � | , and their joint determination from the Cabibbo suppressed hadronic � decays in various perturbative schemes. We improve this analysis compared to the previous analysis based on the optimal renormalization or the renormalization group summed perturbation theory (RGSPT) scheme by replacing the theoretical longitudinal contributions with phenomenological parametrization; the RGSPT coefficients are used for the dimension-4 Adler functions. The improved analysis results in the extraction of � � ( 2     GeV ) = 98 ± 19   MeV and | � � � | = 0.2191 ± 0.0043 from the RGSPT scheme