The dark photon ($A^{\prime }$) production through the mixing with the bremsstrahlung photon from the electron scattering off nuclei can be accompanied by the dominant invisible $A^{\prime }$ decay into dark-sector particles. In this work we discuss the missing energy signature of this process in the experiment NA64 aiming at the search for $A^{\prime }\to \text{invisible}$ decays with a high-energy electron beam at the CERN SPS (The Super Proton Synchrotron). We show the distinctive distributions of variables that can be used to distinguish the $A^{\prime }\to \text{invisible}$ signal from background. The results of the detailed simulation of the detector response for the events with and without $A^{\prime }$ emission are presented. The efficiency of the signal event selection is estimated. It is used to evaluate the sensitivity of the experiment and show that it allows us to probe the still unexplored area of the mixing strength ${10}^{-6}\lesssim \epsilon \lesssim {10}^{-2}$ and masses up to $M_{A^{\prime }}\lesssim 1\mathrm{GeV}$. The results obtained are compared with the results from other calculations. In the case of the signal observation, a possibility of extraction of the parameters $M_{A^{\prime }}$ and $\epsilon$ by using the shape of the missing energy spectrum is discussed.

Employing the so-called hybrid formalism, we calculate the cross section of inclusive hadron production in proton-proton collisions at forward rapidity in small-$x$ formalism at one-loop order. For the case of hadron production at forward rapidity, we can use collinear parton distributions for the projectile proton and $k_{\perp }$-dependent gluon distribution for the target proton. We show that collinear divergences associated with initial- and final-state parton radiations are renormalized into parton distributions and fragmentation functions, respectively, in terms of the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equation. Furthermore, rapidity divergence can be absorbed into the wave function of the target proton, which gives rise to the well-known Balitsky-Fadin-Kuraev-Lipatov equation. These divergences are completely separated from the short-distance partonic hard parts, which is now finite at next-to-leading-order accuracy. The result presented in this paper can be reckoned as a baseline calculation without any nonlinear QCD effects in small-$x$ formalism. As a consistency check, we compare our results with the previous calculation for nonlinear proton-nucleus collisions in small-$x$ formalism and find complete agreement in the dilute and large-$N_c$ limit. In phenomenology, the direct comparison of the above two separate calculations can reveal the role and strength of the nonlinear dynamics in high-energy QCD, and thus help us reliably study the onset of gluon saturation when genuine nonlinear interactions become important.

A study of $B_c^{+}\to K^{+}{K}^{-}{\pi }^{+}$ decays is performed for the first time using data corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ collected by the LHCb experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. Evidence for the decay $B_c^{+}\to {\chi }_{c0}(\to K^{+}{K}^{-}){\pi }^{+}$ is reported with a significance of 4.0 standard deviations, giving $\frac{\sigma (B_c^{+})}{\sigma (B^{+})}\times \mathcal{B}(B_c^{+}\to {\chi }_{c0}{\pi }^{+})=(9.8_{-3.0}^{+3.4}(\mathrm{stat})\pm 0.8(\mathrm{syst}))\times {10}^{-6}$. Here $\mathcal{B}$ denotes a branching fraction while $\sigma (B_c^{+})$ and $\sigma (B^{+})$ are the production cross sections for $B_c^{+}$ and $B^{+}$ mesons. An indication of $\overline{b}c$ weak annihilation is found for the region $m(K^{-}{\pi }^{+})<1.834\mathrm{GeV}/c^2$, with a significance of 2.4 standard deviations.

Recent progress in the holographic approach has made it more transparent that each conductivity can be decomposed into the coherent contribution due to momentum relaxation and the incoherent contribution due to intrinsic current relaxation. In this paper we investigate this decomposition in the framework of Einstein-Maxwell-dilaton theory. We derive the perturbation equations, which are decoupled for a large class of background solutions, and then obtain the analytic results of conductivity with slow momentum relaxation in the low frequency approximation, which is consistent with the known results from memory matrix techniques.

We numerically construct the supersymmetric and non-supersymmetric wave functions of an $\mathcal{N}=4$ quiver quantum mechanics with two Abelian nodes and a single arrow. This model captures the dynamics of a pair of wrapped D-branes interacting via a single light string mode. A dimensionless parameter $\nu$, which is inversely proportional to the Fayet-Iliopoulos parameter, controls whether the bulk of the wave functions are supported on the Higgs branch or the Coulomb branch. We demonstrate how the supersymmetric and excited states morph as $\nu$ is tuned. We also numerically compute the energy gap between the ground state and the first excited states as a function of $\nu$. An expression for the gap, computed on the Coulomb branch, matches nicely with our numerics at large $\nu$ but deviates at small $\nu$ where the Higgs branch becomes the relevant description of the physics. In the appendix, we provide the Schrödinger equations fully reduced via symmetries which, in principle, allow for the numerical determination of the entire spectrum at any point in moduli space. For the ground states, this numerical determination of the spectrum can be thought of as the first in silico check of various Witten index calculations.

We classify the sign of the critical Casimir force between two finite objects separated by a large distance in the two-dimensional systems that can be described by conformal field theory (CFT). Specifically, we show that, as long as the smallest scaling dimension present in the spectrum of the system is smaller than one, the sign of the force is independent of the shape of the objects and can be determined by the elements of the modular $S$ matrix of the CFT. The provided formula for the sign of the force indicates that the force is always attractive for equal boundary conditions, independent of the shape of the objects. However, different boundary conditions can lead to attractive or repulsive forces. Using the derived formula, we prove the known results regarding the Ising model and the free bosons. As new examples, we give detailed results regarding the $Q=3$ state Potts model and the compactified bosons. For example, for the latter model we show that the Dirichlet boundary condition does not always lead to an attractive force.

By considering Hadamard vacuum states, we first construct the two-point functions associated with Stueckelberg massive electromagnetism in de Sitter and anti–de Sitter spacetimes. Then, from the general formalism developed by Belokogne and Folacci [Phys. Rev. D 93, 044063 (2016)], we obtain an exact analytical expression for the vacuum expectation value of the renormalized stress-energy tensor of the massive vector field propagating in these maximally symmetric spacetimes.

In this work we present Finsler gravitational waves. These are a Finslerian version of the well-known $pp$-waves, generalizing the very special relativity line element. Our Finsler $pp$-waves are an exact solution of Finslerian Einstein’s equations in vacuum and describe gravitational waves propagating in an anisotropic background.

In this work, the three-dimensional nonlinearly charged black holes have been considered with a power-law modified electromagnetic theory. The black hole solutions to Einstein’s three-dimensional field equations with a negative cosmological constant have been constructed in the presence of power-law nonlinear electrodynamics. Through the physical and mathematical interpretation of the solutions, a new class of asymptotically anti–de Sitter (AdS) black hole solutions has been introduced. The area law, surface gravity, and Gauss’s law are utilized to obtain the entropy, temperature, and electric charge of the new AdS black holes, respectively. The quasilocal mass of the solutions has been calculated based on the counterterm method. A Smarr-type formula for the mass as a function of entropy and charge has been obtained. It has been shown that the thermodynamical quantities satisfy the first law of thermodynamics for the new AdS black holes. Also, it has been found that in order for the Smarr mass formula to be compatible with the first law of black hole thermodynamics, the cosmological parameter $\mathrm{\Lambda }$ should be treated as a thermodynamical variable and the generalized first law of thermodynamics has been introduced. Through the canonical ensemble method, the black hole remnant or phase transitions have been investigated regarding the black hole heat capacity. It has been found that the AdS black hole solutions we just obtained are thermodynamically stable.

We characterize the expected statistical errors with which the parameters of black hole binaries can be measured from gravitational-wave (GW) observations of their inspiral, merger, and ringdown by a network of second-generation ground-based GW observatories. We simulate a population of black hole binaries with uniform distribution of component masses in the interval $(3,80)M_{\odot }$, distributed uniformly in comoving volume, with isotropic orientations. From signals producing signal-to-noise ratio $\ge 5$ in at least two detectors, we estimate the posterior distributions of the binary parameters using the Bayesian parameter estimation code LALInference. The GW signals will be redshifted due to the cosmological expansion, and we measure only the “redshifted” masses. By assuming a cosmology, it is possible to estimate the gravitational masses by inferring the redshift from the measured posterior of the luminosity distance. We find that the measurement of the gravitational masses will be, in general, dominated by the error in measuring the luminosity distance. In spite of this, the component masses of more than 50% of the population can be measured with accuracy better than $\sim 25\%$ using the Advanced LIGO-Virgo network. Additionally, the mass of the final black hole can be measured with median accuracy $\sim 18\%$. Spin of the final black hole can be measured with median accuracy $\sim 5\%(17\%)$ for binaries with nonspinning (aligned-spin) black holes. Additional detectors in Japan and India significantly improve the accuracy of sky localization, and moderately improve the estimation of luminosity distance, and hence, that of all mass parameters. We discuss the implication of these results on the observational evidence of intermediate-mass black holes and the estimation of cosmological parameters using GW observations.

It is well known that two types of gravitational wave memory exist in general relativity (GR): the linear memory and the nonlinear, or Christodoulou, memory. These effects, especially the latter, depend on the specific form of the Einstein equation. It can then be speculated that, in modified theories of gravity, the memory can differ from the GR prediction and provides novel phenomena to study these theories. We support this speculation by considering scalar-tensor theories, for which we find two new types of memory: the T memory and the S memory, which contribute to the tensor and scalar components of a gravitational wave, respectively. Specifically, the former is caused by the burst of energy carried away by scalar radiation, while the latter is intimately related to the no scalar hair property of black holes in scalar-tensor gravity. We estimate the size of these two types of memory in gravitational collapses and formulate a detection strategy for the S memory, which can be singled out from tensor gravitational waves. We show that (i) the S memory exists even in spherical symmetry and is observable under current model constraints, and (ii) while the T memory is usually much weaker than the S memory, it can become comparable in the case of spontaneous scalarization.

In a recent paper [Ghasemi-Nodehi and Bambi, Eur. Phys. J. C 76, 290 (2016)], we have proposed a new parametrization for testing the Kerr nature of astrophysical black hole candidates. In the present work, we study the possibility of constraining the “Kerr parameters” of our proposal using x-ray reflection spectroscopy, the so-called iron line method. We simulate observations with the LAD instrument on board of the future eXTP mission assuming an exposure time of 200 ks. We fit the simulated data to see if the Kerr parameters can be constrained. If we have the correct astrophysical model, 200 ks observations with LAD/eXTP can constrain all the Kerr parameters with the exception of $b_{11}$, whose impact on the iron line profile is extremely weak and its measurement looks very challenging.

In a recently proposed theory, the cosmological constant (CC) does not curve spacetime in our Universe, but instead gets absorbed into another universe endowed with its own dynamical metric, nonlocally coupled to ours. Thus, one achieves a long standing goal of removing entirely any cosmological constant from our Universe. Dark energy then cannot be due to a cosmological constant, but must be obtained via other mechanisms. Here we focus on the scenario in which dark energy is due to massive gravity and its extensions. We show how the metric of the other universe, that absorbs our CC, also gives rise to the fiducial metric known to be necessary for the diffeomorphism invariant formulation of massive gravity. This is achieved in a framework where the other universe is described by 5D AdS gravity, while our Universe lives on its boundary and is endowed with dynamical massive gravity. A nondynamical pullback of the bulk AdS metric acts as the fiducial metric for massive gravity on the boundary. This framework also removes a difficulty caused by the quantum strongly coupled behavior of massive gravity at the ${\mathrm{\Lambda }}_3$ scale: in the present approach, the massive gravity action does not receive any loop-induced counterterms, despite being strongly coupled.

We extend $k$-inflation which is a type of kinetically driven inflationary model under the standard inflationary scenario to a possible warm inflationary scenario. The dynamical equations of this warm $k$-inflation model are obtained. We rewrite the slow-roll parameters which are different from the usual potential driven inflationary models and perform a linear stability analysis to give the proper slow-roll conditions in warm $k$-inflation. Two cases, a power-law kinetic function and an exponential kinetic function, are studied, when the dissipative coefficient $\mathrm{\Gamma }={\mathrm{\Gamma }}_0$ and $\mathrm{\Gamma }=\mathrm{\Gamma }(\varphi )$, respectively. A proper number of e-folds is obtained in both concrete cases of warm $k$-inflation. We find a constant dissipative coefficient ($\mathrm{\Gamma }={\mathrm{\Gamma }}_0$) is not a workable choice for these two cases while the two cases with $\mathrm{\Gamma }=\mathrm{\Gamma }(\varphi )$ are self-consistent warm inflationary models.

Warm dark matter cosmologies have been widely studied as an alternative to the cold dark matter paradigm, the characteristic feature being a suppression of structure formation on small cosmological scales. A very similar situation occurs if standard cold dark matter particles are kept in local thermal equilibrium with a, possibly dark, relativistic species until the Universe has cooled down to keV temperatures. We perform a systematic phenomenological study of this possibility, and classify all minimal models containing dark matter and an arbitrary radiation component that allows such a late kinetic decoupling. We recover explicit cases recently discussed in the literature and identify new classes of examples that are very interesting from a model-building point of view. In some of these models dark matter is inevitably self-interacting, which is remarkable in view of recent observational support for this possibility. Hence, dark matter models featuring late kinetic decoupling have the potential not only to alleviate the missing satellites problem but also to address other problems of the cosmological concordance model on small scales, in particular the cusp-core and too-big-too-fail problems, in some cases without invoking any additional input.

We show explicitly how the T model, E model, and Hilltop inflations are obtained from the general scalar-tensor theory of gravity with arbitrary conformal factors in the strong coupling limit. We argue that $\xi$ attractors can give any observables $n_s$ and $r$ by this method. The existence of attractors imposes a challenge to distinguish different models.

Modeling the stochastic gravitational wave background from various astrophysical sources is a key objective in view of upcoming observations with ground- and space-based gravitational wave observatories such as Advanced LIGO, VIRGO, eLISA, and the pulsar timing array. We develop a synthetic model framework that follows the evolution of single and binary compact objects in an astrophysical context. We describe the formation and merger rates of binaries, the evolution of their orbital parameters with time, and the spectrum of emitted gravitational waves at different stages of binary evolution. Our approach is modular and allows us to test and constrain different ingredients of the model, including stellar evolution, black hole formation scenarios, and the properties of binary systems. We use this framework in the context of a particularly well-motivated astrophysical setup to calculate the gravitational wave background from several types of sources, including inspiraling stellar-mass binary black holes that have not merged during a Hubble time. We find that this signal, albeit weak, has a characteristic shape that can help constrain the properties of binary black holes in a way complementary to observations of the background from merger events. We discuss possible applications of our framework in the context of other gravitational wave sources, such as supermassive black holes.

We consider low-scale leptogenesis via right-handed neutrinos $N$ coupled to a $Z^{\prime }$ boson, with gauged $U(1{)}_{B-L}$ as a simple realization. Keeping the neutrinos sufficiently out of equilibrium puts strong bounds on the $Z^{\prime }$ coupling strength and mass, our focus being on light $Z^{\prime }$ and $N$, testable in the near future by SHiP, HPS, Belle II, and at the LHC. We show that leptogenesis could be robustly falsified in a large region of parameter space by the double observation of $Z^{\prime }$ and $N$, e.g. in the channel $pp\to Z^{\prime }\to NN$ with displaced $N$-decay vertex, and by several experiments searching for light $Z^{\prime }$, according to the mass of $N$.

We investigate the continuum spectrum of the SU(2) gauge theory with $N_f=2$ flavors of fermions in the fundamental representation. This model provides a minimal template which is ideal for a wide class of Standard Model extensions featuring novel strong dynamics that range from composite (Goldstone) Higgs theories to several intriguing types of dark matter candidates, such as the strongly interacting massive particles (SIMPs). We improve our previous lattice analysis [1] by adding more data at light quark masses, at two additional lattice spacings, by determining the lattice cutoff via a Wilson flow measure of the $w_0$ parameter, and by measuring the relevant renormalization constants nonperturbatively in the regularization-invariant momentum (RI’-MOM) scheme. Our result for the lightest isovector state in the vector channel, in units of the pseudoscalar decay constant, is $m_V/F_{\mathrm{PS}}\sim 13.1(2.2)$ (combining statistical and systematic errors). For the axial channel our result is $m_A/F_{\mathrm{PS}}\sim 14.5(3.6)$, which however does include a similarly sized additional systematic error due to residual excited-states contamination. In the context of the composite (Goldstone) Higgs models, our result for the spin-one resonances are $m_V>3.2(5)\mathrm{TeV}$ and $m_A>3.6(9)\mathrm{TeV}$, which are above the current LHC constraints. In the context of dark matter models, for the SIMP case our results indicate the occurrence of a compressed spectrum at the required large dark pion mass, which implies the need to include the effects of spin-one resonances in phenomenological estimates.

We investigate a simple model using the numerical simulation in the complex Langevin equation (CLE) and the analytical approximation with the Gaussian ansatz. We find that the Gaussian ansatz captures the essential and even quantitative features of the CLE results quite well when they converge to the exact answer, as well as the border of the unstable region where the CLE converges to a wrong answer. The Gaussian ansatz is therefore useful for looking into this convergence problem and we find that the exact answer in the unstable region is nicely reproduced by another solution that is naively excluded from the stability condition. We consider the Gaussian probability distributions corresponding to multiple solutions along the Lefschetz thimble to discuss the stability and the locality. Our results suggest a prescription to improve the convergence of the CLE simulation to the exact answer.