Experimental measurements of $R_D$, $R_{D^{*}}$ and $R_{J/\mathrm{\Psi }}$ in $B\to (D,D^{*})l\nu$ and $B_c\to J/\mathrm{\Psi }l\nu$ decays mediated via $b\to cl\nu$ charged current interactions deviate from standard model prediction by $2.3\sigma$, $3.0\sigma$ and $1.3\sigma$, respectively. In addition, a deviation of $1.5\sigma$ from the standard model prediction has been witnessed in $\mathcal{B}(B\to \tau \nu )$ mediated via $b\to ul\nu$ charged current interactions as well. Motivated by the anomalies present in $B$ and $B_c$ meson decays, we analyze the corresponding $B_s\to (K,K^{*})\tau \nu$ and $B\to \pi \tau \nu$ semileptonic decays within the standard model and beyond. We use an effective field theory formalism in which $b\to c$ and $b\to u$ semileptonic decays are assumed to exhibit similar new physics patterns. We give the predictions of various observables such as the branching fractions, ratio of branching ratios, lepton side forward backward asymmetry, lepton polarization fraction and convexity parameter for $B_s\to (K,K^{*})\tau \nu$ and $B\to \pi \tau \nu$ decay channels within the standard model and within various new physics scenarios.

We examine the necessity of requiring that relaxion dynamics is dominated by classical slow roll and not quantum fluctuations. It has been recently proposed by Nelson and Prescod-Weinstein [Phys. Rev. D 96, 113007 (2017)] that abandoning this requirement can lead to a unified solution of the hierarchy and strong $CP$ problems in QCD relaxion models. In more general models this results in a higher value of the allowed cutoff. In this work we find, however, that relaxing this condition can result in the Universe being dominated in physical volume by regions arising from large quantum fluctuations of the relaxion. These regions turn out to be problematic for the relaxion mechanism because either the relaxion does not stabilize at all or it stabilizes at vacua which cannot reproduce the observed properties of our Universe. The size of these undesirable regions is moreover ambiguous because of the measure problem. For instance, we show that if one chooses to use the scale-factor cutoff measure such dangerous regions occupy a negligible volume and these issues do not arise.

The proton’s tensor charges are calculated at leading order in a symmetry-preserving truncation of all matter-sector equations relevant to the associated bound-state and scattering problems. In particular, the nucleon three-body bound-state equation is solved without using a diquark approximation of the two-body scattering kernel. The computed charges are similar to those obtained in contemporary simulations of lattice-regularized quantum chromodynamics, an outcome which increases the tension between theory and phenomenology. Curiously, the theoretical calculations produce a value of the scale-invariant ratio ($-{\delta }_{T}d/{\delta }_{T}u$) which matches that obtained in simple quark models, even though the individual charges are themselves different. The proton’s tensor charges can be used to constrain extensions of the Standard Model using empirical limits on nucleon electric dipole moments.

We consider the production of pairs of lepton through the Drell-Yan process at the LHC and present the most accurate prediction on their rapidity distribution. While the fixed order prediction is already known to next-to-next-to-leading order in perturbative QCD, the resummed contribution coming from threshold region of phase space up to next-to-next-to-leading logarithmic (NNLL) accuracy has been computed in this article. The formalism developed in [1–3] has been used to resum large threshold logarithms in the two dimensional Mellin space to all orders in perturbation theory. We have done a detailed numerical comparison against other approaches that resum certain threshold logarithms in Mellin-Fourier space. Our predictions at NNLL level are close to theirs even though at leading logarithmic and next-to-leading logarithmic level we differ. We have also investigated the impact of these threshold logarithms on the stability of perturbation theory against factorization and renormalization scales. While the dependence on these scales does not get better with resummed results, the convergence of the perturbative series shows a better trend compared to the fixed order predictions. This is evident from the reduction in the K-factor for the resummed case compared to fixed order. We also present the uncertainties on the predictions resulting from parton distribution functions.

Neutrino-nucleus scattering $\nu A\to \nu A$, in which the nucleus conserves its integrity, is considered. Our consideration follows a microscopic description of the nucleus as a bound state of its constituent nucleons described by a multiparticle wave function of a general form. We show that elastic interactions keeping the nucleus in the same quantum state lead to a quadratic enhancement of the corresponding cross section in terms of the number of nucleons. Meanwhile, the cross section of inelastic processes in which the quantum state of the nucleus is changed, essentially has a linear dependence on the number of nucleons. These two classes of processes are referred to as coherent and incoherent, respectively. Accounting for all possible initial and final internal states of the nucleus leads to a general conclusion independent of the nuclear model. The coherent and incoherent cross sections are driven by factors $|F_{p/n}{|}^2$ and $(1-|F_{p/n}{|}^2)$, where $|F_{p/n}{|}^2$ is a proton/neutron form factor of the nucleus, averaged over its initial states. Therefore, our assessment suggests a smooth transition between regimes of coherent and incoherent neutrino-nucleus scattering. In general, both regimes contribute to experimental observables. The coherent cross-section formula used in the literature is revised and corrections depending on kinematics are estimated. Consideration of only those matrix elements which correspond to the same initial and final spin states of the nucleus and accounting for a nonzero momentum of the target nucleon are two main sources of the corrections. As an illustration of the importance of the incoherent channel, we considered three experimental setups with different nuclei. As an example, for ${}^{133}\mathrm{Cs}$ and neutrino energies of 30–50 MeV, the incoherent cross section is about 10%–20% of the coherent contribution if the experimental detection threshold is accounted for. Experiments attempting to measure coherent neutrino scattering by solely detecting the recoiling nucleus, as is typical, might be including an incoherent background that is indistinguishable from the signal if the excitation gamma eludes its detection. However, as is shown here, the incoherent component can be measured directly by searching for photons released by the excited nuclei inherent to the incoherent channel. For a beam experiment these gammas should be correlated in time with the beam, and their higher energies make the corresponding signal easily detectable at a rate governed by the ratio of incoherent to coherent cross sections. The detection of signals due to the nuclear recoil and excitation $\gamma \mathrm{s}$ provides a more sensitive instrument in studies of nuclear structure and possible signs of new physics.

A search for the rare decay $\eta \to e^{+}{e}^{-}$ is performed using the inverse process $e^{+}{e}^{-}\to \eta$ in the decay mode $\eta \to {\pi }^0{\pi }^0{\pi }^0$. We analyze data with an integrated luminosity of $654{\mathrm{nb}}^{-1}$ accumulated at the VEPP-2000 $e^{+}{e}^{-}$ collider with the SND detector at the center-of-mass energy $E=m_{\eta }{c}^2\approx 548\mathrm{MeV}$, and set the upper limit $\mathcal{B}(\eta \to e^{+}{e}^{-})<7\times {10}^{-7}$ at the 90% confidence level.

The difficulty of describing the gauge dependent biquark condensate in the QCD color superconducting phase has made it hard to construct a holographic dual of the state. To side step this problem, we argue that near the chiral restoration transition in the temperature-chemical potential plane, the strongly coupled gluons are likely completely gapped so that the color quantum numbers of the quarks can be thought of below that gap as global indices. A standard anti-de Sitter–superconductor model can then be used to analyze the fermionic gap formation. We investigate the role of four-fermion interactions, which might be used to include the gapped QCD interactions, on the vacuum and metastable vacua of the model. It turns out to be easiest to simply relate the standard interaction of the holographic superconductor to the strength of the gapped gluons. The result is a holographic description of the QCD color superconducting phase diagram. We take a first look at how quark mass enters and causes a transition between the color-flavor locked phase and the two flavor color superconducting phase.

In loop quantum gravity, the area element of embedded spatial surfaces is given by a well-defined operator. We further characterize the quantized geometry of such surfaces by proposing definitions for operators quantizing scalar curvature and mean curvature. By investigating their properties, we shed light on the nature of the geometry of surfaces in loop quantum gravity. We also investigate the entanglement entropy across surfaces in the case where spin network edges are running within the surface. We observe that, on a certain class of states, the entropy gradient across a surface is proportional to the mean curvature. In particular, the entanglement entropy is constant for small deformations of a minimal surface in this case.

Twisted gravitational waves (TGWs) are nonplanar unidirectional Ricci-flat solutions of general relativity. Thus far only TGWs of Petrov type II are implicitly known that depend on a solution of a partial differential equation and have wave fronts with negative Gaussian curvature. A special Petrov type $D$ class of such solutions that depends on an arbitrary function is explicitly studied in this paper and its Killing vectors are worked out. Moreover, we concentrate on two solutions of this class, namely, the Harrison solution and a simpler solution we call the $w$-metric and determine their Penrose plane-wave limits. The corresponding transition from a nonplanar TGW to a plane gravitational wave is elucidated.

We propose a viable dark energy scenario in the presence of cubic Horndeski interactions and a standard scalar-field kinetic term with two exponential potentials. We show the existence of new scaling solutions along which the cubic coupling $G_3$ provides an important contribution to the field density that scales in the same way as the background fluid density. The solutions finally exit to the epoch of cosmic acceleration driven by a scalar-field dominated fixed point arising from the second exponential potential. We clarify the viable parameter space in which all the theoretically consistent conditions including those for the absence of ghost and Laplacian instabilities are satisfied on scaling and scalar-field dominated critical points. In comparison to quintessence with the same scalar potential, we find that the cubic coupling gives rise to some novel features: (i) the allowed model parameter space is wider in that a steeper potential can drive the cosmic acceleration; (ii) the dark energy equation of state $w_{\varphi }$ today can be closer to $-1$ relative to quintessence; (iii) even if the density associated with the cubic coupling dominates over the standard field density in the scaling era, the former contribution tends to be suppressed at low redshifts. We also compute quantities associated with the growth of matter perturbations and weak lensing potentials under the quasi-static approximation in the subhorizon limit and show that the cubic coupling leads to the modified evolution of perturbations which can be distinguished from quintessence.

Motivated by the GW170817/GRB170817A constraint on the deviation of the speed of gravitational waves from that of photons, we study disformal transformations of the metric in the context of the generalized Proca theory. The constraint restricts the form of the gravity Lagrangian, the way the electromagnetism couples to the gravity sector on cosmological backgrounds, or in general a combination of both. Since different ways of coupling matter to gravity are typically related to each other by disformal transformations, it is important to understand how the structure of the generalized Proca Lagrangian changes under disformal transformations. For disformal transformations with constant coefficients we provide the complete transformation rule of the Lagrangian. We find that additional terms, which were considered as beyond generalized Proca in the literature, are generated by the transformations. Once these additional terms are included, on the other hand, the structure of the gravity Lagrangian is preserved under the transformations. We then derive the transformation rules for the sound speeds of the scalar, vector and tensor perturbations on a homogeneous and isotropic background. We explicitly show that they transform following the natural expectation of metric transformations, that is, according to the transformation of the background lightcone structure. We end by arguing that inhomogeneities due to structures in the universe, e.g., dark matter halos, generically changes the speed of gravitational waves from its cosmological value. Therefore, even if the propagation speed of gravitational waves in a homogeneous and isotropic background is fine-tuned to that of light (at linear level), the model is subject to further constraints (at non-linear level) due to the presence of inhomogeneities. We give a rough estimate of the effect of inhomogeneities and find that the fine-tuning should not depend on the background or that the fine-tuned theory has to be further fine-tuned to pass the tight constraint.

Closed photon orbits around isolated black holes are related to important aspects of black hole physics, such as strong lensing, absorption cross section of null particles and the way that black holes relax through quasinormal ringing. When two black holes are present—such as during the inspiral and merger events of interest for gravitational-wave detectors—the concept of closed photon orbits still exist, but its properties are basically unknown. With these applications in mind, we study here the closed photon orbits of two different static black hole binaries. The first one is the Majumdar-Papapetrou geometry describing two extremal, charged black holes in equilibrium, while the second one is the double sink solution of fluid dynamics, which describes (in a curved-spacetime language) two “dumb” holes. For the latter solution, we also characterize its dynamical response to external perturbations and study how it relates to the photon orbits. In addition, we compute the ergoregion of such spacetime and show that it does not coincide with the event horizon.

Assuming that, for a given source of gravitational waves (GWs), we know its sky position, as is the case for GW events with an electromagnetic counterpart such as GW170817, we discuss a null stream method to probe GW polarizations including spin-0 (scalar) GW modes and spin-1 (vector) modes, especially with an expected network of Advanced LIGO, Advanced Virgo, and KAGRA. For two independent null streams for four noncoaligned GW detectors, we study a location on the sky, exactly at which the spin-0 modes of GWs vanish in any null stream for the GW detector network, though the strain output at a detector may contain the spin-0 modes. Our numerical calculations show that there exist 70 sky positions that satisfy this condition of killing the spin-0 modes in the null streams. If a GW source with an electromagnetic counterpart is found in one of the 70 sky positions, the spin-1 modes will be testable separately from the spin-0 modes by the null stream method. In addition, we study a superposition of the two null streams to show that any one of the three modes (one combined spin-0 and two spin-1 modes) can be eliminated by suitably adjusting a weighted superposition of the null streams and thereby a set of the remaining polarization modes can be experimentally tested.

Making use of the T-duality symmetry of superstring theory and of the double geometry from double field theory, we argue that cosmological singularities of a homogeneous and isotropic universe disappear. In fact, an apparent big bang singularity in Einstein gravity corresponds to a universe expanding to infinite size in the dual dimensions.

The presence of massive particles with spin during inflation induces distinct signatures on correlation functions of primordial curvature fluctuations. In particular, the bispectrum of primordial perturbations obtains an angular dependence determined by the spin of the particle, which can be used to set constraints on the presence of such particles. If these particles are long-lived on super-Hubble scales, as is the case, e.g., for partially massless particles, their imprint on correlation functions of curvature perturbations would be unsuppressed. In this paper, we make a forecast for how well such angular dependence can be constrained by the upcoming EUCLID spectroscopic survey via the measurement of the galaxy bispectrum.

We introduce Weyl’s scale invariance as additional local symmetry in the standard model of electroweak interactions. Under this, the gauge symmetry of the standard model now is $SU(3)\times SU(2)\times U(1)\times \tilde{U}(1)$, where $\tilde{U}(1)$ is for local scale invariance, and its gauge boson is called the Weylon. Also introduced are two new scalars ${\sigma }_1$ and ${\sigma }_2$ with the common scaling weight $-1$. The mechanism for spontaneous breaking of scale invariance is invoked by coupling ${\sigma }_2$ to a metric-independent measure defined in terms of an additional four scalars ${\varphi }^I(I=1,2,3,4)$. Weyl’s scale invariance is now implemented by combining it with internal diffeomorphisms of the four scalars ${\varphi }^i$. We show that once local scale invariance is broken, the phenomenon (a) generates Newton’s gravitational constant $G_N$ and (b) triggers spontaneous symmetry breaking in the conventional manner resulting in masses for the conventional fermions and bosons. The scale at which Weyl’s scale symmetry breaks is of order Planck mass. If right-handed neutrinos are also introduced, their absence at present energy scales is attributed to their mass being tied to the scale at which scale invariance breaks. New $C$- and $CP$-violating effects can also be induced by mixing the Weylon with the hypercharge gauge boson of the standard model.

The goal of ForwArd Search ExpeRiment (FASER) at the LHC is to discover light, weakly interacting particles with a small and inexpensive detector placed in the far-forward region of ATLAS or CMS. A promising location in an unused service tunnel 480 m downstream of the ATLAS interaction point (IP) has been identified. Previous studies have found that FASER has significant discovery potential for new particles produced at the IP, including dark photons, dark Higgs bosons, and heavy neutral leptons. In this study, we explore a qualitatively different, “beam dump” capability of FASER, in which the new particles are produced not at the IP, but through collisions in detector elements further downstream. In particular, we consider the discovery prospects for axionlike particles (ALPs) that couple to the standard model through the $a\gamma \gamma$ interaction. TeV-scale photons produced at the IP collide with the TAXN neutral particle absorber 130 m downstream, producing ALPs through the Primakoff process, and the ALPs then decay to two photons in FASER. We show that FASER can discover ALPs with masses $m_a\sim 30–400\mathrm{MeV}$ and couplings $g_{a\gamma \gamma }\sim {10}^{-6}-{10}^{-3}{\mathrm{GeV}}^{-1}$, and we discuss the ALP signal characteristics and detector requirements.

We study correlation functions of spatially separated static quark-antiquark pairs in ($2+1$)-flavor QCD in order to investigate onset and nature of color screening at high temperatures. We perform lattice calculations in a wide temperature range, $140\le T\le 5814\mathrm{MeV}$, using the highly improved staggered quark action and several lattice spacings to control discretization effects. By comparing at high temperatures our lattice results to weak-coupling calculations, as well as to the zero temperature result for the energy of a static quark-antiquark pair, we observe that color screening sets in at $rT\approx 0.3$. Furthermore, we also observe that in the range $0.3\lesssim rT\lesssim 0.6$ weak-coupling calculations in the framework of suitable effective field theories provide an adequate picture of color screening.

We study the radiative (E1 and M1) decays of P-wave quarkonia in a strong magnetic field based on the Lagrangian of potential nonrelativistic QCD. To investigate their properties, we implement a polarized wave function basis justified in the Paschen-Back limit. In a magnetic field stronger than the spin-orbit coupling, the wave functions of the P-wave quarkonia are drastically deformed by the Hadronic Paschen-Back effect. Such deformation leads to the anisotropy of the direction of decays from the P-wave quarkonia. The analytic formulas for the radiative decay widths in the nonrelativistic limit are shown, and the qualitative decay properties are discussed.

Properties of the Higgs boson are measured in the two-photon final state using $36.1{\mathrm{fb}}^{-1}$ of proton–proton collision data recorded at $\sqrt{s}=13\mathrm{TeV}$ by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon–gluon fusion, vector-boson fusion, and in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of $0.99\pm 0.14$ improves on the precision of the ATLAS measurement at $\sqrt{s}=7$ and 8 TeV by a factor of two. Measurements of gluon–gluon fusion and vector-boson fusion productions yield signal strengths compatible with the Standard Model prediction. Measurements of simplified template cross sections, designed to quantify the different Higgs boson production processes in specific regions of phase space, are reported. The cross section for the production of the Higgs boson decaying to two isolated photons in a fiducial region closely matching the experimental selection of the photons is measured to be $55\pm 10\mathrm{fb}$, which is in good agreement with the Standard Model prediction of $64\pm 2\mathrm{fb}$. Furthermore, cross sections in fiducial regions enriched in Higgs boson production in vector-boson fusion or in association with large missing transverse momentum, leptons or top-quark pairs are reported. Differential and double-differential measurements are performed for several variables related to the diphoton kinematics as well as the kinematics and multiplicity of the jets produced in association with a Higgs boson. These differential cross sections are sensitive to higher order QCD corrections and properties of the Higgs boson, such as its spin and $CP$ quantum numbers. No significant deviations from a wide array of Standard Model predictions are observed. Finally, the strength and tensor structure of the Higgs boson interactions are investigated using an effective Lagrangian, which introduces additional $CP$-even and $CP$-odd interactions. No significant new physics contributions are observed.