We discuss production of far-forward charm and anticharm quarks, $D$ mesons and antimesons, and neutrinos and antineutrinos from their semileptonic decays in proton-proton collisions at the LHC energies. We include the gluon-gluon fusion $gg\to c\overline{c}$, the intrinsic charm (IC) $gc\to gc$ as well as the recombination $gq\to Dc$ partonic mechanisms. The calculations are performed within the $k_T$-factorization approach and the hybrid model using different unintegrated parton distribution functions (uPDFs) for gluons from the literature, as well as within the collinear approach. We compare our results to the LHCb data for forward $D^0$-meson production at $\sqrt{s}=13\mathrm{TeV}$ for different rapidity bins in the interval $2<y<4.5$. A good description is achieved for the Martin-Ryskin-Watt (MRW) uPDF. We also show results for the Kutak-Sapeta (KS) gluon uPDF, both in the linear form and including nonlinear effects. The nonlinear effects play a role only at very small transverse momenta of $D^0$ or ${\overline{D}}^0$ mesons. The IC and recombination models are negligible at the LHCb kinematics. Both the mechanisms start to be crucial at larger rapidities and dominate over the standard charm production mechanisms. At high energies, there are so far no experiments probing this region. We present uncertainty bands for the both mechanisms. Decreased uncertainty bands will be available soon from fixed-target charm experiments in $pA$ collisions. We present also energy distributions for forward electron, muon, and tau neutrinos to be measured at the LHC by the currently operating $\mathrm{FASER}\nu$ experiment, as well as by future experiments like $\mathrm{FASER}\nu 2$ or FLArE, proposed very recently by the Forward Physics Facility project. Again components of different mechanisms are shown separately. For all kinds of neutrinos (electron, muon, tau), the subleading contributions, i.e., the IC and/or the recombination, dominate over light meson (pion, kaon) and the standard charm production contribution driven by fusion of gluons for neutrino energies $E_{\nu }\gtrsim 300\mathrm{GeV}$. For electron and muon neutrinos, both the mechanisms lead to similar production rates, and their separation seems rather impossible. On the other hand, for ${\nu }_{\tau }+{\overline{\nu }}_{\tau }$ neutrino flux, the recombination is further reduced making the measurement of the IC contribution very attractive.

Recently, the BESIII Collaboration has measured the $D_s^{+}\to {\pi }^0{K}^{+}{K}_S^0$ decay and reported the observation of scalar meson $a_0(1710{)}^{+}$ in the $K^{+}{K}_S^0$ invariant mass spectrum. Based on the previous study about such a state in the $D_s^{+}\to {\pi }^{+}{K}_S^0{K}_S^0$ decay, we perform a theoretical study of $a_0(1710{)}^{+}$ in the process $D_s^{+}\to {\pi }^0{a}_0(1710{)}^{+}\to {\pi }^0{K}^{+}{K}_S^0$. In addition to the $a_0(1710)$ state, the contributions of $K^{*}$ and $a_0(980)$ are also taken into account. Firstly, we consider the contributions from the tree diagrams of $K^{*+}\to K^{+}{\pi }^0$ and ${\overline{K}}^{*0}\to {\pi }^0{\overline{K}}^0$. Secondly, we describe the final state interaction of $K\overline{K}$ in the chiral unitary approach to study the contribution of $a_0(980)$, while the $a_0(1710)$ state is dynamically generated from the $K^{*}{\overline{K}}^{*}$ interaction, and then decays into $K^{+}{\overline{K}}^0$. Since the final $K^{+}{K}_S^0$ state is in pure isospin $I=1$, the $D_s^{+}\to {\pi }^0{K}^{+}{K}_S^0$ decay is an ideal process to study the $a_0(1710{)}^{+}$ and $a_0(980{)}^{+}$ resonances. It is found that the recent BESIII experimental measurements on the $K^{+}{K}_S^0$, ${\pi }^0{K}^{+}$, and ${\pi }^0{K}_S^0$ invariant mass distributions can be well reproduced, which supports the molecular $K^{*}{\overline{K}}^{*}$ nature of the scalar $a_0(1710)$ resonance.

A new form of the Kerr-Newman solution is presented. The solution involves a time coordinate which represents the local proper time for a charged massive particle released from rest at spatial infinity. The chosen coordinates ensure that the solution is well-behaved at horizons and enable an intuitive description of many physical phenomena. If the charge of the particle $e=0$, the coordinates reduce to Doran coordinates for the Kerr solution with the replacement $M\to M-Q^2/(2r)$, where $M$ and $Q$ are the mass and charge of the black hole, respectively. Such coordinates are valid only for $r\ge Q^2/(2M)$, however, which corresponds to the region that a neutral particle released from rest at infinity can penetrate. By contrast, for $e\ne 0$ and of opposite sign to $Q$, the new coordinates have a progressively extended range of validity as $|e|$ increases and tend to advanced Eddington-Finkelstein (EF) null coordinates as $|e|\to \infty$, hence becoming global in this limit. The Kerr solution (i.e. with $Q=0$) may also be written in terms of the new coordinates by setting $eQ=-\alpha$, where $\alpha$ is a real parameter unrelated to charge; in this case the coordinate system is global for all non-negative values of $\alpha$ and the limits $\alpha =0$ and $\alpha \to \infty$ correspond to Doran coordinates and advanced EF null coordinates, respectively, without any need to transform between them.

For the case of two light flavors we propose the stringy description of the system consisting of two heavy and three light quarks, with the aim of exploring the quark organization inside the system and its low-lying Born-Oppenheimer potentials as a function of the heavy quark separation. Our analysis reveals several critical separations related to the processes of string reconnection, breaking and junction annihilation. We find that a compact pentaquark configuration makes the dominant contribution to the potential of the first excited state at small separations, and for separations larger than 0.1 fm, the antiquark-diquark-diquark structure emerges. Moreover, it turns out that the length scale of string junction annihilation is the same as that for the $QQ\overline{q}\overline{q}$ system. We also discuss the relation to the potential of the $QQq$ system and some relations among the masses of hadrons in the heavy quark limit.

A method to study electromagnetic (EM) effects generated by a straight null cosmic string moving in classical EM fields is suggested. The string is shown to induce an additional EM field which can be described as a solution to homogeneous Maxwell equations with initial data set on a null surface, the string event horizon, which the string world sheet belongs to. The initial data ensure the required holonomy of the string space-time caused by the gravity of the string. This characteristic initial value problem is used to study the interaction of plane waves with null strings and perturbations by the strings of the Coulomb fields of electric charges. It is shown that parts of an incoming EM wave crossing the string horizon from different sides of the string are refracted with respect to each other and leave behind the string a wedgelike region of interference. A null string moving near an electric charge results in two effects: it creates a self-force of the charge and induces a pulse of EM radiation traveling away from the charge in the direction close to the trajectory of the string.

We consider the Brill metric, which is an electrovacuum solution to Einstein’s field equation. It depends on three parameters, a mass parameter $m$, a NUT parameter $l$, and a charge parameter $e$. If the charge parameter is small, the metric describes a black hole; if it is sufficiently big, it describes a wormhole. We determine the relevant lensing features both in the black-hole and the wormhole case. In particular, we give formulas for the photon spheres, for the angular radius of the shadow, and for the deflection angle. We illustrate the lensing features with the help of an effective potential and in terms of embedding diagrams. To that end we make use of the fact that each lightlike geodesic is contained in a (coordinate) cone and that it is a geodesic of a Riemannian optical metric on this cone. By the Gauss-Bonnet theorem, the sign of the Gaussian curvature of the optical metric determines the sign of the deflection angle. In the wormhole case the deflection angle may be negative, which means that light rays are repelled from the center.

The connection dynamics of the five-dimensional Kaluza-Klein theory reduced on four-dimensional spacetime is obtained by performing the Hamiltonian analysis and canonical transformations. Deparametrization is achieved in the spherically symmetric model of the theory without introducing additional matter fields beyond the five-dimensional gravity. Thus the physical time evolution and the physical spatial coordinate can be provided by the geometrical degrees of freedom in the higher dimensional spacetime.

We apply common gravitational wave inference procedures on binary black hole merger waveforms beyond general relativity. We consider dynamical Chern-Simons gravity, a modified theory of gravity with origins in string theory and loop quantum gravity. This theory introduces an additional parameter $\ell$, corresponding to the length-scale below which beyond-general-relativity effects become important. We simulate data based on numerical relativity waveforms produced under an approximation to this theory, which differ from those of general relativity in the strongly nonlinear merger regime. We consider a system with parameters similar to GW150914 with different values of $\ell$ and signal-to-noise ratios. We perform two analyses of the simulated data. The first is a template-based analysis that uses waveforms derived under general relativity and allows us to identify degeneracies between the two waveform morphologies. The second is a morphology-independent analysis based on bayeswave that does not assume that the signal is consistent with general relativity. The bayeswave analysis faithfully reconstructs the simulated signals. However, waveform models derived under general relativity are unable to fully mimic the simulated modified-gravity signals and such a deviation would be identifiable with existing inference tools. Depending on the magnitude of the deviation, we find that the templated analysis can under perform the morphology-independent analysis in fully recovering simulated beyond-GR waveforms even for achievable signal-to-noise ratios $\gtrsim 20–30$.

In this work, we study the inversion temperature associated with the Joule-Thomson expansion from the thermodynamics of AdS-Reissner-Nördstrom black holes. We include quantum corrections in a cosmological fluid that can describe phantom dark matter or quintessence, both in a Kiselev scenario. The description of such physical systems involves numerical solutions, and the results are presented as temperature-pressure plots for various values of the parameters of our model. We find nonzero minimum inversion temperatures as well as nonzero minimum pressures depending on the values of those parameters. Completing our study, we also find isenthalpic curves associated with black hole fixed mass processes.

All energy is gravitational energy. That is the consequence of the equivalence principle, according to which gravity is the universal interaction. The physical charges of this interaction have remained undisclosed, but the advent of the geometrical trinity opened a new approach to this foundational problem. Here it is shown to provide a background-independent unification of the previous, noncovariant approaches of Bergmann-Thomson, Cooperstock, Einstein, von Freud, Landau-Lifshitz, Papapetrou, and Weinberg. First, the Noether currents are derived for a generic Palatini theory of gravity coupled with generic matter fields, and then the canonical, i.e., the unique charges, are robustly derived and analyzed, particularly in the metric teleparallel and the symmetric teleparallel versions of general Relativity. These results, and their application to black holes and gravitational waves, are new.

We consider Einstein-Maxwell-dilaton theory in ($2+1$) dimensions where the coupling between the scalar field and the Maxwell invariant is the dilatonic coupling $f(\varphi )=\exp (-2\alpha \varphi )$, and we obtain novel, exact, rotating black hole solutions. The dilatonic parameter $\alpha$ impacts the metric function, affecting the rotating properties of the black hole, its mass, and also its thermodynamics. Calculating the entropy we find that it is always positive, and the dilatonic black holes may have higher entropy than the BTZ black hole. Depending on the parameters, the dilatonic BTZ-like black hole may be thermodynamically preferred over the BTZ black hole which is recovered when $\alpha =0$.

We generalize the combinatorial algebraic approach first proposed by Dhurandhar et al. to construct various classes of modified second-generation time-delay interferometry (TDI) solutions. The main idea behind the original algorithm is to enumerate, in a given order, a specific type of commutator between two monomials defined by the products of particular time-displacement operators. On the one hand, the enumeration process can be implemented using the properties of the commutative ring and the relevant equation for the TDI solution. On the other hand, these commutators are shown to vanish if we only keep up the first-order contributions regarding the rate of change of armlengths. In other words, each commutator furnishes a valid TDI solution pertaining to the given type of modified second-generation combinations. In this work, Dhurandhar’s algorithm, which only involved time-delay operators and was primarily applied to Michelson-type solutions, is extended by introducing the time-advance ones and then utilized to seek combinations of the Beacon, Relay, Monitor, Sagnac, and fully symmetric Sagnac types. We discuss the relation between the present scheme’s solutions and those obtained by the geometric TDI approach, a well-known method of exhaustion of virtual optical paths. In particular, we report the results on novel Sagnac-inspired solutions that cannot be straightforwardly obtained using the geometric TDI algorithm. The average response functions, floor noise power spectral densities, and sensitivity functions are evaluated for the obtained solutions.

Gaussian noise is an irreducible component of the background in gravitational wave (GW) detectors. Although stationary Gaussian noise is uncorrelated in frequencies, we show that there is an important correlation in time when looking at the matched filter signal-to-noise ratio (SNR) of a template, with a typical autocorrelation time that depends on the template and the shape of the noise power spectral density (PSD). Taking this correlation into account, we compute from first principles the false alarm rate (FAR) of a template in Gaussian noise, defined as the number of occurrences per unit time that the template’s matched filter SNR goes over a threshold $\rho$. We find that the Gaussian FAR can be well approximated by the usual expression for uncorrelated noise, if we replace the sampling rate by an effective sampling rate that depends on the parameters of the template, the noise PSD, and the threshold $\rho$. This results in a minimum SNR threshold needed for a given GW trigger, if we want to keep events generated from Gaussian noise below a certain FAR. We extend the formalism to multiple detectors and to the analysis of GW events. We apply our method to the GW candidates added in the GWTC-3 catalog and discuss the possibility that GW200308_173609 and GW200322_091133 could be generated by Gaussian noise fluctuations.

We develop a new relativistic radiation hydrodynamics code based on the Monte Carlo algorithm. In this code, we implement a new scheme to achieve the second-order accuracy in time in the limit of a large packet number for solving the interaction between matter and radiation. This higher-order time-integration scheme is implemented in the manner to guarantee the energy-momentum conservation to the precision of the geodesic integrator. The spatial dependence of radiative processes, such as the packet propagation, emission, absorption, and scattering, are also taken into account up to the second-order accuracy. We validate our code by solving various test problems on a fixed-background metric following the previous studies; one-zone thermalization, dynamical diffusion, radiation dragging, radiation-mediated shock-tube, shock-tube in the optically-thick limit, and Eddington limit problems. We show that our code reproduces physically appropriate results with reasonable accuracy and also demonstrate that the second-order accuracy in time and space is indeed achieved with our implementation for one-zone and one-dimensional problems.

Lightning dart leaders and recoil leaders are current pulses that propagate along previously established lightning channels reionizing the channel. They are poorly understood since it is not known how a previously ionized channel can undergo dielectric breakdown multiple times. In this work we investigate five recoil leaders on two different channels using lightning observations of the LOFAR radio telescope in vhf (where we observe 30–80 MHz) using our TRI-D interferometric imaging algorithm. We show that while recoil leaders do slow down over time on average, they can also clearly accelerate. In addition, the vhf power emitted by the recoil leader is closely correlated with speed. We also investigate the vhf-emitting width of the recoil leaders and show that it is thinner than our meter-scale resolution. This shows that recoil leaders have significant streamer activity in their channel core or at most very inner region of the corona sheath, and that there is either very little, or weakly vhf-emitting, streamer activity in the majority of the corona sheath. Finally, we show that recoil leaders can have small microsecond-scale fluctuations in emitted vhf power that can occur in the same spot across subsequent recoil leaders on the same channel, demonstrating that recoil leader propagation is affected by small-scale channel geometry.

The flavor symmetry-breaking scale in the Froggatt-Nielsen (FN) mechanism is very weakly constrained by present experiments and can lie anywhere between a few TeVs and the Planck scale. We construct two minimal, nonsupersymmetric, ultraviolet complete models that generate the FN mechanism, with a global $U(1{)}_{\mathrm{FN}}$ flavor symmetry and a single flavon field. Using the one-loop finite temperature effective potential, we explore the possibility of a strong first order phase transition induced by the flavon. We show that if the flavor symmetry breaking occurs at intermediate scales $\sim {10}^4–{10}^7\mathrm{GeV}$, then in certain regions of the parameter space, the associated stochastic gravitational wave (GW) background is strong enough to be detected by second-generation GW observatories such as the Big Bang Observer, the Deci-hertz interferometer Gravitational Observatory, the Cosmic Explorer, and the Einstein Telescope. We identify viable regions of the parameter space for the best detection prospects. While both models of flavor can produce a detectable GW background, the GW signature does not discriminate between them.