A minimal extension of the Standard Model (SM) featuring two scalar leptoquarks, an SU(2) doublet with hypercharge $1/6$ and a singlet with hypercharge $1/3$, is proposed as an economical benchmark model for studies of an interplay between flavor physics and properties of the neutrino sector. The presence of such type of leptoquarks radiatively generates neutrino masses and offers a simultaneous explanation for the current $B$-physics anomalies involving $b\to c\ell {\nu }_{\ell }$ decays. The model can also accommodate both the muon magnetic moment and the recently reported $W$-mass anomalies, while complying with the most stringent lepton flavor-violating observables.

Several hints of the presence of a new state at about 95 GeV have been observed recently. The CMS and ATLAS Collaborations have reported excesses in the diphoton channel at about this diphoton invariant mass with local statistical significances of $2.9\sigma$ and $1.7\sigma$, respectively. Furthermore, a $2\sigma$ excess in the $b\overline{b}$ final state was also observed at LEP, again pointing at a similar mass value. We interpret these intriguing hints of new physics in a variant of the Scotogenic model, an economical scenario that induces Majorana neutrino masses at the loop level and includes a viable dark matter candidate. We show that our model can explain the 95 GeV excesses while respecting the relevant collider, Higgs, and electroweak precision bounds and discuss other phenomenological features of our scenario.

We compute the bulk, $\zeta$, and shear, $\eta$, viscosity over entropy density, $s$, for the QCD matter formed in small collision systems at LHC. We consider a scenario of the string percolation model by proposing a global form of the color reduction factor that describes both the thermodynamic limit and its maximum deviation due to small-bounded effects. Our method involves estimations at vanishing baryon-chemical potential, assuming local equilibrium for string clusters in the initial state. To compute $\eta /s$, we employed a kinetic approach that accounts QCD states as an ideal gas of partons, while $\zeta /s$ is computed by using two different approaches: a simple kinetic formula and the causal dissipative relativistic fluid dynamics formulation. Our results align with lattice QCD computations and Bayesian methods and are consistent with holographic conjecture bounds. Furthermore, our findings support the notion of a strongly interacting medium, similar to that observed in nuclear collisions, albeit with a phase transition occurring outside the thermodynamic limit.

The spectrum of the charmed meson-(anti)meson system is a fundamental tool for disentangling the nature of a few exotic hadrons, including the recently discovered $T_{cc}^{+}(3875)$ tetraquark, the $X(3960)$, or the $X(3872)$, the nature of which is still not clear after almost two decades of its discovery. Here we consider that the charmed meson-(anti)meson short-range interaction is described by the exchange of light mesons ($\sigma$, $\rho$, $\omega$). The effects of light-meson exchanges are recast into a simple contact-range theory by means of a saturation procedure, resulting in a compact description of the two-hadron interaction. From this, if the $T_{cc}^{+}$ were to be an isoscalar $D^{*}D$ molecule, then there should exist an isoscalar $J=1$ $D^{*}{D}^{*}$ partner, as constrained by heavy-quark spin symmetry. Yet, within our model, the most attractive two charmed meson configurations are the isovector $J=0$ $D^{*}{D}^{*}$ molecule and its sextet $D_s^{*}{D}^{*}$ and $D_s^{*}{D}_s^{*}$ flavor partners. Finally, we find a tension between the molecular descriptions of the $T_{cc}^{+}$ and that of the $X(3872)$ and $X(3960)$, where most parameter choices suggest that if the $T_{cc}^{+}$ is purely molecular then the $X(3872)$ overbinds [or conversely, if the $X(3872)$ is a molecule the $T_{cc}^{+}$ does not bind]. This might be consequential for determining the nature of these states.

We present an analysis on the sensitivity to the active-sterile neutrino mixing with Germanium (Ge) and Silicon (Si) detectors in the context of the proposed coherent elastic neutrino-nucleus experiment in India. The study has been carried out with 3 $(\mathrm{active})+1(\mathrm{sterile})$ neutrino oscillation model. It is observed that the measurements that can be carried out with the Ge detector exhibit better sensitivity to the active-sterile neutrino mixing as compared to the Si detector. Both detectors are able to exclude most of the anomaly regions observed by the GALLIUM experiment. The Ge detector with mass 10 kg, can observe the active-sterile neutrino oscillation at 95% confidence level, provided that ${\sin }^{2}2{\theta }_{14}\ge 0.09$ at $\mathrm{\Delta }{m}_{41}^2=1.0{\mathrm{eV}}^2$ for an exposure of 1-yr. At higher values of $\mathrm{\Delta }{m}_{41}^2$, a better sensitivity is obtained at a short baseline. It is also found that the threshold as well as resolution of the detectors play a crucial role on the measurements of active-sterile neutrino mixing parameters.

The ${\tau }^{-}\to {\pi }^{-}\eta {\nu }_{\tau }$ decay is forbidden in the Standard Model in the limit of exact $G$-parity, it becomes a rare decay due to isospin symmetry breaking and it is very sensitive to the effects of effective scalar interactions. Since the parameters driving isospin breaking, $(m_d-m_u)/(m_s-\overline{m})$ and $\alpha$, are of the same order, one may expect their $G$-parity breaking effects in this decay can be of similar magnitudes. In this work, we evaluate the effects of isospin-breaking amplitudes originated from a virtual photon at one-loop in a resonance dominance model to describe photon-hadron interactions. We find that these effects can shift the leading SM predictions for the decay rate based on the $u-d$ quark mass difference by roughly $({13.5}_{-4.1}^{+4.9})\%$, and should be taken into consideration in a precision comparison of theory and experiment in order to draw meaningful conclusions on new physics. The effects in the decay rate of the analogous${\tau }^{-}\to {\pi }^{-}{\eta }^{\prime }{\nu }_{\tau }$ decay can be larger, $(78\pm 38)\%$, within the approximations assumed in this model. The uncertainty in the former channel is dominated by the input parameters of the resonance model, while the uncertainty in the latter is due to the ${\pi }^0{\eta }^{\prime }$ mixing parameter.

By analyzing $7.33{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we search for the semileptonic decays $D_s^{+}\to K_1(1270{)}^0{e}^{+}{\nu }_e$ and $D_s^{+}\to b_1(1235{)}^0{e}^{+}{\nu }_e$ for the first time. No significant signals are observed for either decay mode. The upper limits on the (product) branching fractions are determined to be $\mathcal{B}[D_s^{+}\to K_1(1270{)}^0{e}^{+}{\nu }_e]<4.1\times {10}^{-4}$ and $\mathcal{B}[D_s^{+}\to b_1(1235{)}^0{e}^{+}{\nu }_e]·\mathcal{B}[b_1(1235{)}^0\to \omega {\pi }^0]<6.4\times {10}^{-4}$ at 90% confidence level.

Using $e^{+}{e}^{-}$ collision data with an integrated luminosity of $7.33{\mathrm{fb}}^{-1}$ collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector operating at the BEPCII collider, the branching fraction of the leptonic decay $D_s^{+}\to {\mu }^{+}{\nu }_{\mu }$ is measured to be $(0.5294\pm 0.0108_{\mathrm{stat}}\pm 0.0085_{\mathrm{syst}})\%$. Based on this, the product of the $D_s^{+}$ decay constant $f_{D_s^{+}}$ and the magnitude of the $c\to s$ quark mixing matrix element $|V_{cs}|$ is determined to be $f_{D_s^{+}}|V_{cs}|=241.8\pm {2.5}_{\mathrm{stat}}\pm {2.2}_{\mathrm{syst}}\mathrm{MeV}$. Using the value of $|V_{cs}|$ given by the global standard model fit, $f_{D_s^{+}}$ is found to be $248.4\pm {2.5}_{\mathrm{stat}}\pm {2.2}_{\mathrm{syst}}\mathrm{MeV}$. Alternatively, using the value of $f_{D_s^{+}}$ from a recent lattice quantum chromodynamics calculation, $|V_{cs}|$ is determined to be $0.968\pm 0.010_{\mathrm{stat}}\pm 0.009_{\mathrm{syst}}$.

We discuss a continuous family of nonsupersymmetric ${\mathrm{AdS}}_3\times S^3\times {\mathrm{T}}^4$ vacua in heterotic and type II supergravities whose complete Kaluza-Klein spectrum is computed and found to be free from instabilities. This family is protected as well against some nonperturbative decay channels, and as such it provides the first candidate for a nonsupersymmetric holographic conformal manifold in 2D. We also describe the operators realizing the deformations in the world sheet and boundary conformal field theories.

The discrepancies between $b\to s{\ell }^{+}{\ell }^{-}$ data and the corresponding Standard Model predictions point to the existence of new physics with a significance at the $5\sigma$ level. While previously a lepton flavor universality violating effect was preferred, the new $R(K^{(*)})$ and $B_s\to {\mu }^{+}{\mu }^{-}$ measurements are now compatible with the Standard Model, favoring a lepton flavor universal beyond the Standard Model contribution to $C_9$. Since heavy new physics is generally chiral, and because of the stringent constraints from charged lepton flavor violation, this poses a challenge for model building. In this article, we point out a novel possibility: a diquark, i.e., a colored scalar, induces the Wilson coefficient of the $(\overline{s}{\gamma }^{\mu }{P}_{L}b)(\overline{c}{\gamma }_{\mu }{P}_{L}c)$ operator at tree-level, which then mixes into $O_9$ via an off-shell photon penguin. This setup allows for a lepton flavor universal effect of $C_9\approx -0.5$, without violating bounds from $\mathrm{\Delta }{M}_s$, $\mathrm{\Delta }\mathrm{\Gamma }$, $B\to X_s\gamma$ and $D^0-{\overline{D}}^0$ mixing. This scenario predicts a small and negative $C_9^{\prime }$ and a light diquark, preferably with a mass around 500 GeV, as compatible with the CMS di-dijet analysis, and a deficit in the inclusive $b\to c\overline{c}s$ rate.

As basic quantum mechanical models, anharmonic oscillators are recently revisited by bootstrap methods. An effective approach is to make use of the positivity constraints in Hermitian theories. There exists an alternative avenue based on the null state condition, which applies to both Hermitian and non-Hermitian theories. In this work, we carry out an analytic bootstrap study of the quartic oscillator based on the weak coupling expansion. In the Hamiltonian formalism, we obtain the anharmonic generalization of Dirac’s ladder operators. Furthermore, the Schrödinger equation can be interpreted as a null state condition generated by an anharmonic ladder operator. This provides an explicit example in which dynamics is incorporated into the principle of nullness. In the Lagrangian formalism, we show that the existence of null states can effectively eliminate the indeterminacy of the Dyson-Schwinger equations and systematically determine $n$-point Green’s functions.

We analyze the adiabatic regularization scheme to renormalize Proca fields in a four-dimensional Friedmann-Lemaître-Robertson-Walker spacetime. The adiabatic method is well established for scalar and spin-$1/2$ fields, but is not yet fully understood for spin-1 fields. We give the details of the construction and show that, in the massless limit, the renormalized stress-energy tensor of the Proca field is closely related to that of a minimally coupled scalar field. Our result is in full agreement with other approaches, based on the effective action, which also show a discontinuity in the massless limit. The scalar field can be naturally regarded as a Stüeckelberg-type field. We also test the consistency of our results in de Sitter space.

The Lorentz symmetry of gravity is spontaneously broken when the nonminimally coupled Kalb-Ramond field acquires a nonzero vacuum expectation value. In this work, we present exact solutions for static and spherically symmetric black holes in the framework of this Lorentz-violating gravity theory. In order to explore the physical implications of Lorentz violation, we analyze the thermodynamic properties of the obtained solutions and evaluate the impact of Lorentz violation on some classical gravitational experiments within the Solar System. Furthermore, the Lorentz-violating parameter is constrained by using the measured results of these experiments.

We study extreme-mass-ratio systems in theories admitting the Schwarzschild solution and propagating a massive graviton. We show that, in addition to small corrections to the quadrupolar and higher-order modes, a dipolar mode is excited in these theories, and we quantify its excitation. While LIGO-Virgo-KAGRA observations are not expected to impose meaningful constraints in the dipolar sector, future observations by the Einstein Telescope or by LISA, together with bounds from dispersion relations, can rule out theories of massive gravity admitting vacuum General Relativistic backgrounds. For the bound to be circumvented, one needs to move away from Ricci-flat solutions and enter a territory where constraints based on wave propagation and dispersion relations are not reliable.

I derive a smooth and global Kruskal-Szekeres coordinate chart for the maximal extension of the Reissner-Nordström geometry that provides a generalization to the standard inner and outer Kruskal-Szekeres coordinates. The Kruskal-Szekeres diagram associated to this coordinate chart, whose existence is an interesting fact in and of itself, provides a simple alternative to the conformal diagram of the spacetime.

We consider the explicit analytic behavior of photon escape cones in generic static spherically symmetric spacetimes, emphasizing the interplay between the physical spacetime metric and the optical metric, and the interplay between large-distance asymptotic and near-horizon physics. The circular photon orbits (photon spheres) are shown to be given by wormhole throats in the optical metric, (not the physical metric), and the escape cone solid angle is easily calculable in terms of the capture cross section ${\sigma }_{\mathrm{capture}}$, the area of the spherical 2-surfaces, and the norm of the timelike Killing vector. Under appropriate circumstances, for near-horizon photon emission the escape cone solid angle can be related to the surface gravity ${\kappa }_H$. We provide a number of illustrative examples, involving both black holes and wormholes, including situations with multiple photon spheres.

Recent observations from weak gravitational lensing (WL) surveys indicate a smoother Universe compared to the predictions of the cosmic microwave background (CMB). This inconsistency is commonly referred to as the ${\sigma }_8$ tension or $S_8$ tension, where ${\sigma }_8$ represents the present root-mean-square matter fluctuation averaged over a sphere of radius $8h^{-1}\mathrm{Mpc}$, and $S_8\equiv {\sigma }_8\sqrt{{\mathrm{\Omega }}_m/0.3}$. In this article, we investigate a kind of general Dirac-Born-Infeld (DBI) Lagrangian referred to as the surface-type DBI (sDBI) model. We find that up to the linear order, the constraints on the sDBI model with high-redshift probe (CMB) and low-redshift probes (WL and galaxy clustering, GC) yield $S_8={0.7448}_{-0.21}^{+0.031}$ and ${0.7426}_{-0.085}^{+0.054}$, respectively. Remarkably, these values not only demonstrate self-consistency but also align with the values obtained from the majority of low-redshift probes. Furthermore, we present a discussion on exploring the nonlinear effects of this model, which holds the potential to address additional challenges associated with cold dark matter (CDM) on small scales.

In this work we revisit power law, $\frac{1}{M^2}{R}^{\beta }$, inflation to find the deviations from $R^2$ inflation allowed by current cosmic microwave background (CMB) and large-scale structure (LSS) observations. We compute the power spectra for scalar and tensor perturbations numerically and perform Markov chain Monte Carlo analysis to put constraints on parameters $M$ and $\beta$ from Planck-2018, BICEP3 and other LSS observations. We consider general reheating scenario and also vary the number of $e$-foldings during inflation, $N_{\text{pivot}}$, along with the other parameters. We find $\beta ={1.966}_{-0.042}^{+0.035}$, $M=({3.31}_{-2}^{+5})\times {10}^{-5}$ and $N_{\text{pivot}}={41}_{-10}^{+10}$ with 95% C.L. This indicates that the current observations allow deviation from Starobinsky inflation. The scalar spectral index, $n_s$, and tensor-to-scalar ratio, $r$, derived from these parameters, are consistent with the Planck and BICEP3 observations.

The abundance of primordial black holes changes in the presence of local non-Gaussianity. A positive nonlinear parameter $f_{\mathrm{NL}}$ increases the abundance while a negative one reduces it. We show that in nonattractor single-field models of inflation which enhance the curvature power spectrum and may give rise to primordial black holes, $f_{\mathrm{NL}}$ is always positive, when computed in correspondence of the peak of the curvature power spectrum where the primordial black hole abundance has its maximum. This implies that the interpretation of the recent pulsar timing arrays data from scalar-induced gravitational waves generated at primordial black hole formation may not be supported by invoking non-Gaussianity within nonattractor single-field models.

The hot big bang model predicts the existence of a cosmic neutrino background. The number of particles and antiparticles in this primordial bath of neutrinos can be different—a memory of processes that took place at very early epochs. If neutrinos were massless, this asymmetry would not change once neutrinos froze out. However, in the case of massive particles, the asymmetry is not protected by conservation laws and can get erased via helicity-flipping scatterings off matter inhomogeneities. We evaluate this helicity-flipping rate and demonstrate that if relic lepton asymmetry ever existed, it would remained largely intact in the Earth’s neighborhood for realistic values of neutrino masses.