General metric theories in a four-dimensional spacetime allow at most six polarization states (two spin-0, two spin-1, and two spin-2) of gravitational waves (GWs). If a sky location of a GW source with the electromagnetic counterpart satisfies a single equation that we propose in this paper, both the spin-1 modes and spin-2 ones can be eliminated from a certain combination of strain outputs at four ground-based GW interferometers (e.g., a network of aLIGO-Hanford, aLIGO-Livingston, Virgo, and KAGRA), where this equation describes curves on the celestial sphere. This means that, if a GW source is found in the curve (or its neighborhood practically), a direct test of scalar (spin-0) modes separately from the other (vector and tensor) modes becomes possible in principle. The possibility of such a direct test is thus higher than an earlier expectation (Hagihara et al., Phys. Rev. D 100, 064010 (2019)), in which they argued that the vector modes could not be completely eliminated. We discuss also that adding the planned LIGO-India detector as a fifth detector will increase the feasibility of scalar polarization tests.

Assuming dislocations could be meaningfully described by torsion, we propose here a scenario based on the role of time in the low-energy regime of two-dimensional Dirac materials, for which coupling of the fully antisymmetric component of the torsion with the emergent spinor is not necessarily zero. Appropriate inclusion of time is our proposal to overcome well-known geometrical obstructions to such a program, that stopped further research of this kind. In particular, our approach is based on the realization of an exotic time-loop, that could be seen as oscillating particle-hole pairs. Although this is a theoretical paper, we moved the first steps toward testing the realization of these scenarios, by envisaging Gedankenexperiments on the interplay between an external electromagnetic field (to excite the pair particle-hole and realize the time-loops), and a suitable distribution of dislocations described as torsion (responsible for the measurable holonomy in the time-loop, hence a current). Our general analysis here establishes that we need to move to a nonlinear response regime. We then conclude by pointing to recent results from the interaction laser-graphene that could be used to look for manifestations of the torsion-induced holonomy of the time-loop, e.g., as specific patterns of suppression/generation of higher harmonics.

We explored the possibility that Higgs coupling to new physics violates flavor universality. In particular, we parametrize such models with dimension-six effective operators which modify the coupling between the first generation quarks, Higgs boson, and $Z$ boson. Through the use of boosted Higgsstrahlung events at both the HL-LHC and potential future hadron colliders, as well as existing ATLAS data for background estimates, we projected constraints on the scale of new physics as a function of the Wilson coefficient. The high energy $Zh$ process will provide unique information about these class of operators, and the sensitivity is competitive with the LEP electroweak precision measurements. We include different scenarios of the overall systematic uncertainties and the PDF uncertainties when presenting the projected sensitivities. We also discuss the constraints from flavor changing neutral currents to these flavor-violating models and the complementarity of the exotic Higgs decay to the $Zh$ process.

That massless dark photons could exist and have flavor-changing magnetic-dipole interactions with down-type light quarks is an attractive possibility which may be realized in various new-physics scenarios. It is potentially testable not only in kaon processes but also via two-body hyperon decays involving missing energy carried away by the massless dark photon. We explore the latter within a simplified model approach and take into account constraints from the kaon sector. We find that the branching fractions of some of these hyperon modes are allowed to be as high as a few times $10^{-4}$. Such numbers are likely to be within the sensitivity reaches of ongoing experiments like BESIII and future ones at super charm-tau factories.

New gauge bosons at the MeV scale with tiny gauge couplings (so-called dark photons) can be responsible for the freeze-in production of dark matter and provide a clear target for present and future experiments. We study the effects of thermal mixing between dark photons and Standard Model gauge bosons and of the resulting plasmon decays on dark matter production before and after the electroweak phase transition. In the parameter regions preferred by the observed dark matter relic abundance, the dark photon is sufficiently long-lived to be probed with fixed-target experiments and light enough to induce direct detection signals. Indeed, current limits from XENON1T already constrain Dirac fermion dark matter in the GeV to TeV range produced via the freeze-in mechanism. We illustrate our findings for the case of a $U(1{)}_{B-L}$ gauge extension and discuss possible generalizations.

In this work we assess the transferability of deep learning models to detect beyond the standard model signals. For this we trained deep neural networks on three different signal models: $tZ$ production via a flavor changing neutral current, pair production of vectorlike $T$-quarks via standard model gluon fusion and via a heavy gluon decay in a grid of three mass points: 1, 1.2 and 1.4 TeV. These networks were trained with $t\overline{t}$, $Z+\text{jets}$ and dibosons as the main backgrounds. Limits were derived for each signal benchmark using the inference of networks trained on each signal independently, so that we can quantify the degradation of their discriminative power across different signal processes. We determine that the limits are compatible within uncertainties for all networks trained on signals with vectorlike $T$-quarks, whether they are produced via heavy gluon decay or standard model gluon fusion. The network trained on flavor changing neutral current signal, while struggling the most on the other signals, still produces reasonable limits. These results indicate that deep learning models are capable of providing sensitivity in the search for new physics even if it manifests itself in models not assumed during training.

We present a model in which an up-type vectorlike quark (VLQ) is charged under a new $U(1{)}_d$ gauge force which kinetically mixes with the Standard Model hypercharge. The gauge boson of the $U(1{)}_d$ is the dark photon, ${\gamma }_d$. Traditional searches for VLQs rely on decays into Standard Model electroweak bosons $W$, $Z$, or Higgs. However, since no evidence for VLQs has been found at the Large Hadron Collider (LHC), it is imperative to search for other novel signatures of VLQs beyond their traditional decays. As we show, if the dark photon is much less massive than the Standard Model electroweak sector, $M_{{\gamma }_d}\ll M_Z$, for the large majority of the allowed parameter space the VLQ predominately decays into the dark photon and the dark Higgs that breaks the $U(1{)}_d$. That is, this VLQ is a “maverick top partner” with nontraditional decays. One of the appeals of this scenario is that pair production of the VLQ at the LHC occurs through the strong force and the rate is determined by the gauge structure. Hence, the production of the dark photon at the LHC only depends on the strong force and is largely independent of the small kinetic mixing with hypercharge. This scenario provides a robust framework to search for a light dark sector via searches for heavy colored particles at the LHC.

Until recently little was known about the high-dimensional operators of the standard model effective field theory (SMEFT). However, in the past few years the number of these operators has been counted up to mass dimension 15 using techniques involving the Hilbert series. In this work I will show how to perform the same counting with a different method. This alternative approach makes it possible to cross-check results (it confirms the SMEFT numbers), but it also provides some more information on the operators beyond just counting their number. The considerations made here apply equally well to any other model besides SMEFT and, with this purpose in mind, they were implemented in a computer code.

We consider double $gg\to g$ production in the presence of a bias on the unintegrated gluon distribution of the colliding hadrons or nuclei. Such bias could be due to the selection of configurations with a greater number of gluons or higher mean transverse momentum squared or, more generally, due to a modified spectral shape of the gluon distribution in the hadrons. Hence, we consider reweighted functional averages over the stochastic ensemble of small-$x$ gluons. We evaluate explicitly the double inclusive gluon transverse momentum spectrum in high-energy collisions, and their azimuthal correlations, for a few simple examples of biases.

The hadronic two-body weak decays of the doubly charmed baryons ${\mathrm{\Xi }}_{cc}^{++},{\mathrm{\Xi }}_{cc}^{+}$, and ${\mathrm{\Omega }}_{cc}^{+}$ are studied in this work. To estimate the nonfactorizable contributions, we work in the pole model for the $P$-wave amplitudes and current algebra for $S$-wave ones. For the ${\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{+}{\pi }^{+}$ mode, we find a large destructive interference between factorizable and nonfactorizable contributions for both $S$- and $P$-wave amplitudes. Our prediction of $\sim 0.70\%$ for its branching fraction is smaller than the earlier estimates in which nonfactorizable effects were not considered, but agrees nicely with the result based on an entirely different approach, namely, the covariant confined quark model. On the contrary, a large constructive interference was found in the $P$-wave amplitude by Dhir and Sharma, leading to a branching fraction of order (7–16)%. Using the current results for the absolute branching fractions of $({\mathrm{\Lambda }}_c^{+},{\mathrm{\Xi }}_c^{+})\to p{K}^{-}{\pi }^{+}$ and the LHCb measurement of ${\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{+}{\pi }^{+}$ relative to ${\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Lambda }}_c^{+}{K}^{-}{\pi }^{+}{\pi }^{+}$, we obtain $\mathcal{B}({\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{+}{\pi }^{+}{)}_{\text{expt}}\approx (1.83\pm 1.01)\%$ after employing the latest prediction of $\mathcal{B}({\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Sigma }}_c^{++}{\overline{K}}^{*0})$. Our prediction of $\mathcal{B}({\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{+}{\pi }^{+})\approx 0.7\%$ is thus consistent with the experimental value but in the lower end. It is important to pin down the branching fraction of this mode in future study. Factorizable and nonfactorizable $S$-wave amplitudes interfere constructively in ${\mathrm{\Xi }}_{cc}^{+}\to {\mathrm{\Xi }}_c^0{\pi }^{+}$. Its large branching fraction of order 4% may enable experimentalists to search for the ${\mathrm{\Xi }}_{cc}^{+}$ through this mode. That is, the ${\mathrm{\Xi }}_{cc}^{+}$ is reconstructed through the ${\mathrm{\Xi }}_{cc}^{+}\to {\mathrm{\Xi }}_c^0{\pi }^{+}$ followed by the decay chain ${\mathrm{\Xi }}_c^0\to {\mathrm{\Xi }}^{-}{\pi }^{+}\to p{\pi }^{-}{\pi }^{-}{\pi }^{+}$. Besides ${\mathrm{\Xi }}_{cc}^{+}\to {\mathrm{\Xi }}_c^0{\pi }^{+}$, the ${\mathrm{\Xi }}_{cc}^{+}\to {\mathrm{\Xi }}_c^{+}({\pi }^0,\eta )$ modes also receive large nonfactorizable contributions to their $S$-wave amplitudes. Hence, they have large branching fractions among ${\mathrm{\Xi }}_{cc}^{+}\to {\mathcal{B}}_c+P$ channels. Nonfactorizable amplitudes in ${\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{\prime +}{\pi }^{+}$ and ${\mathrm{\Omega }}_{cc}^{+}\to {\mathrm{\Xi }}_c^{\prime +}{\overline{K}}^0$ are very small compared to the factorizable ones owing to the Pati-Woo theorem for the inner $W$-emission amplitude. Likewise, nonfactorizable $S$-wave amplitudes in ${\mathrm{\Xi }}_{cc}^{+}\to {\mathrm{\Xi }}_c^{\prime +}({\pi }^0,\eta )$ decays are also suppressed by the same mechanism.

A search for the direct production of the supersymmetric partners of $\tau$-leptons (staus) in final states with two hadronically decaying $\tau$-leptons is presented. The analysis uses a dataset of $pp$ collisions corresponding to an integrated luminosity of $139{\mathrm{fb}}^{-1}$, recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one $\tau$-lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidence level for a massless lightest neutralino.

Using a sample of $(448.1\pm 2.9)\times {10}^6$ $\psi (3686)$ events collected with the BESIII detector, we perform the first partial wave analysis of $\psi (3686)\to K^{+}{K}^{-}\eta$. In addition to the well established states, $\varphi (1020)$, $\varphi (1680)$, and $K_3^{*}(1780)$, contributions from $X(1750)$, $\rho (2150)$, ${\rho }_3(2250)$, and $K_2^{*}(1980)$ are also observed. The $X(1750)$ state is determined to be a $1^{--}$ resonance. The simultaneous observation of the $\varphi (1680)$ and $X(1750)$ indicates that the $X(1750)$, with previous observations in photoproduction, is distinct from the $\varphi (1680)$. The masses, widths, branching fractions of $\psi (3686)\to K^{+}{K}^{-}\eta$, and the intermediate resonances are also measured.

We present the first results for the $\mathcal{O}(\alpha {\alpha }_s)$ corrections to the total partonic cross section of the process $q\overline{q}\to Z+X$, with the complete set of contributions, that include photonic and massive weak gauge boson effects. The results are relevant for the precise determination of the hadronic $Z$ boson production cross section. Virtual and real corrections are calculated analytically using the reduction to the master integrals and their evaluation through differential equations. Real corrections are dealt with using the reverse-unitarity method. They require the evaluation of a new set of two-loop master integrals, with up to three internal massive lines. In particular, three of them are expressed in terms of elliptic integrals. We verify the absence, at this perturbative order, of initial-state mass singularities proportional to a weak massive virtual correction to the quark-gluon splitting.

Interesting theories with short range interactions include QCD in the hadronic phase and cold atom systems. The scattering length in a two-to-two elastic scattering process captures the most elementary features of the interactions, such as whether they are attractive or repulsive. However, even this basic quantity is notoriously difficult to compute from first principles in strongly coupled theories. We present a method to compute the two-to-two amplitudes and the scattering length using the holographic duality. Our method is based on the identification of the residues of Green’s functions in the gravity dual with the amplitudes in the field theory. To illustrate the method we compute a contribution to the scattering length in a hard wall model with a quartic potential and find a constraint on the scaling dimension of a scalar operator $\mathrm{\Delta }>d/4$. For $d<4$ this is more stringent than the unitarity constraint and may be applicable to an extended family of large-$N$ theories with a discrete spectrum of massive states. We also argue that for scalar potentials with polynomial terms of order $K$, a constraint more restrictive than the unitarity bound will appear for $d<2K/(K-2)$.

The vacuum expectation value (VEV) of the fermionic current density is investigated in the geometry of two parallel branes in locally AdS spacetime with a part of spatial dimensions compactified to a torus. Along the toral dimensions quasiperiodicity conditions are imposed with general phases and the presence of a constant gauge field is assumed. The influence of the latter on the VEV is of the Aharonov-Bohm type. Different types of boundary conditions are discussed on the branes, including the bag boundary condition and the conditions arising in $Z_2$-symmetric braneworld models. Nonzero vacuum currents appear along the compact dimensions only. In the region between the branes they are decomposed into the brane-free and brane-induced contributions. Both these contributions are periodic functions of the magnetic flux enclosed by compact dimensions with the period equal to the flux quantum. Depending on the boundary conditions, the presence of the branes can either increase or decrease the vacuum current density. For a part of boundary conditions, a memory effect is present in the limit when one of the branes tends to the AdS boundary. Unlike to the fermion condensate and the VEV of the energy-momentum tensor, the VEV of the current density is finite on the branes. Applications are given to higher-dimensional generalizations of the Randall-Sundrum models with two branes and with toroidally compact subspace. The features of the fermionic current are discussed in odd-dimensional parity and time-reversal symmetric models. The corresponding results for three-dimensional spacetime are applied to finite length curved graphene tubes threaded by a magnetic flux. It is shown that a nonzero current density can also appear in the absence of the magnetic flux if the fields corresponding to two different points of the Brillouin zone obey different boundary conditions on the tube edges.

A 250-year-old Newtonian problem, first studied by Euler, turns out to share a lot of similarities with the most extreme astrophysical relativistic object, the Kerr black hole. Although the framework behind the two fields is completely different, both problems are related to gravitational fields that have quite intriguing analogies with respect to orbital motions of a test body within them. The fundamental reason behind their extraordinary similarity is the integrability of both problems, as well as their common multipolar structure. In this paper, we demonstrate the existence of a multitude of qualitative, and sometimes quantitative, similarities between the two problems. Based on this analogy, one could use the Newtonian problem to get insight in cases where the relativistic treatment of the field of a Kerr black hole becomes quite complicated.

It is shown that the Kerr solution exists in the generalized hybrid metric-Palatini gravity theory and that for certain choices of the function $f(R,\mathcal{R})$ that characterizes the theory, the Kerr solution can be stable against perturbations on the scalar degree of freedom of the theory. We start by verifying which are the most general conditions on the function $f(R,\mathcal{R})$ that allow for the general relativistic Kerr solution to also be a solution of this theory. We perform a scalar perturbation in the trace of the metric tensor, which in turn imposes a perturbation in both the Ricci and Palatini scalar curvatures. To first order in the perturbation, the equations of motion, namely the field equations and the equation that relates the Ricci and the Palatini curvature scalars, can be rewritten in terms of a fourth-order wave equation for the perturbation $\delta R$ which can be factorized into two second-order massive wave equations for the same variable. The usual ansatz and separation methods are applied and stability bounds on the effective mass of the Ricci scalar perturbation are obtained. These stability regimes are studied case by case and specific forms of the function $f(R,\mathcal{R})$ that allow for a stable Kerr solution to exist within the perturbation regime studied are obtained.

Recently, numerical solutions to the field equations of Einstein-scalar–Gauss-Bonnet (EsGB) gravity that correspond to black holes with nontrivial scalar hair have been reported. Here, we employ the method of the continued-faction expansion in terms of a compact coordinate in order to obtain an analytical approximation for the aforementioned solutions. For a wide variety of coupling functionals to the Gauss-Bonnet term we were able to obtain analytical expressions for the metric functions and the scalar field. In addition we estimated the accuracy of these approximations by calculating the black-hole shadows for such black holes. Excellent agreement between the numerical solutions and analytical approximations has been found.

We investigate here the locally naked singularity formed due to a spherically symmetric inhomogeneous collapsing cloud having nonzero isotropic pressure, in terms of its strength. A sufficient condition provided by Clarke and Krolak for it to be Tipler strong has been used to restrict the parameters that represent the nonlinear relation between the physical radius and the radial coordinate of the outgoing radial null geodesic at the singular center. Studying an end state of a collapsing cloud requires information about the dynamics of collapse, which is unknown in a general scenario. Hence we study small perturbations to the mass profile for inhomogeneous dust, which is possible using the formalism developed here. This perturbed mass profile, in turn, gives rise to nonzero pressure. We show the existence of a nonzero measure set of initial data giving rise to such strong curvature naked singularity.