We present predictions for the ${\gamma }^{*}N\to N^{*}$ helicity amplitudes, where $N^{*}$ is a member of the $[70,1^{-}]$ supermultiplet. We combine the results from the single quark transition model for the helicity amplitudes with the results of the covariant spectator quark model for the ${\gamma }^{*}N\to N^{*}(1535)$ and ${\gamma }^{*}N\to N^{*}(1520)$ transitions. The theoretical estimations from the covariant spectator quark model are used to calculate three independent functions $A,B$, and $C$ of $Q^2$, where $Q^2=-q^2$ and $q$ is the momentum transfer. With the knowledge of the functions $A,B$, and $C$ we estimate the helicity amplitudes for the transitions ${\gamma }^{*}N\to N^{*}(1650)$, ${\gamma }^{*}N\to N^{*}(1700)$, ${\gamma }^{*}N\to \mathrm{\Delta }(1620)$, and ${\gamma }^{*}N\to \mathrm{\Delta }(1700)$. The analysis is restricted to reactions with proton targets. The predictions for the transition amplitudes are valid for $Q^2>2{\mathrm{GeV}}^2$.

The underlying mixing of scalar mesons is studied in ${\eta }^{\prime }\to \eta \pi \pi$ decay within a generalized linear sigma model of low-energy QCD, which contains two nonets of scalar mesons and two nonets of pseudoscalar mesons (a quark-antiquark nonet and a four-quark nonet). The model has been previously employed in various investigations of the underlying mixings among scalar mesons below and above 1 GeV (as well as those of their pseudoscalar chiral partners) and has provided a coherent global picture for the physical properties and quark substructure of these states. The potential of the model is defined in terms of two- and four-quark chiral nonets and based on the number of underlying quark and antiquark lines in each term in the potential, a criterion for limiting the number of terms at each order of calculation (and systematically further improving the results thereafter). At the leading order, which corresponds to neglecting terms in the potential with higher than eight quark and antiquark lines, the free parameters of the model have been previously fixed in detailed global fits to scalar and pseudoscalar experimental mass spectra below and above 1 GeV together with several low-energy parameters. In the present work, the same order of potential with fixed parameters is used to further explore the underlying mixings among scalar mesons in the ${\eta }^{\prime }\to \eta \pi \pi$ decay. It is found that the linear sigma model with only a single lowest-lying nonet is not accurate in predicting the decay width, but inclusion of the mixing of this nonet with the next-to-lowest-lying nonet, together with the effect of the final-state interaction of pions, significantly improves this prediction and agrees with the experiment up to about 1%. It is also shown that, while the prediction of the leading order of the generalized model for the Dalitz parameters is not close to the experiment, the model is able to give a reasonable prediction of the energy dependencies of the normalized decay amplitude squared and that this is expected to improve with further refinement of the complicated underlying mixings. Overall, this investigation provides further support for the global picture of scalar mesons: those below 1 GeV are predominantly four-quark states and significantly mix with those above 1 GeV, which are closer to the conventional p-wave quark-antiquark states.

We examine the possibilities for constructing models with Dirac gaugino masses and unification of gauge couplings. We identify one promising model and discuss to what extent it can have a “natural” supersymmetric (SUSY) spectrum. We then determine the low-energy constraints upon it, and propose a constrained set of boundary conditions at the unification scale. We describe the implementation of these boundary conditions in the spectrum-generator generator SARAH and we perform a first exploration of the parameter space, specifically searching for points where the spectrum is relatively light. It is shown that the pattern of the masses of SUSY states is very different compared to any expectations from the constrained minimal supersymmetric Standard Model.

We propose an approach to quantum theory based on the energetic causal sets, introduced in [M. Cortês and L. Smolin, arXiv:1307.6167]. Fundamental processes are causal sets for which the events carry momentum and energy, which are transmitted along causal links and conserved at each event. Fundamentally there are amplitudes for such causal processes, but no space-time. An embedding of the causal processes in an emergent space-time arises only at the semiclassical level. Hence, fundamentally there are no commutation relations, no uncertainty principle and, indeed, no $\hslash$. All that remains of quantum theory is the relationship between the absolute value squared of complex amplitudes and probabilities. Consequently, we find that neither locality nor nonlocality is a primary concept; only causality exists at the fundamental level.

This paper addresses the question of whether Witten’s proof of positive Arnowitt-Deser-Misner (ADM) energy for classical general relativity [E. Witten, Commun. Math. Phys. 80, 381 (1981)] can be extended to give a proof of positive energy for a nonperturbative quantization of general relativity. To address this question, a set of conditions is shown to be sufficient for showing the positivity of a Hamiltonian operator corresponding to the ADM energy. One of these conditions is a particular factor ordering for the constraints of general relativity, in a representation where the states are functionals of the Ashtekar connection, and the auxiliary, Witten spinor.

We study and numerically compute the scattering coefficients of shallow water waves blocked by a stationary counterflow. When the flow is transcritical, the coefficients closely follow Hawking’s prediction according to which black holes should emit a thermal spectrum. We study how the spectrum deviates from thermality when reducing the maximal flow velocity, with a particular attention to subcritical flows since these have been recently used to test Hawking’s prediction. For such flows, we show that the emission spectrum is strongly suppressed, and that its Planckian character is completely lost. For low frequencies, we also show that the scattering coefficients are dominated by elastic hydrodynamical channels. Our numerical results reproduce rather well the observations made by S. Weinfurtner et al. in the Vancouver experiment. Nevertheless, we propose a new interpretation of what has been observed, as well as new experimental tests.

The cosmological constant is treated as a thermodynamical parameter in the framework of two-dimensional dilaton gravity. We find that the cosmological constant behaves as a $U(1)$ charge with a confining potential, and that such potentials require a novel Born-Infeld boundary term in the action. The free energy and other thermodynamical quantities of interest are derived, from first principles, in a way that is essentially model independent. We discover that there is always a Schottky anomaly in the specific heat and explain its physical origin. Finally, we apply these results to specific examples, like anti-de Sitter–Schwarzschild–Tangherlini black holes, Bañados-Teitelboim-Zanelli black holes and the Jackiw-Teitelboim model.

We study the large $N_c$ behavior of couplings among light meson states with different compositions in terms of quarks and gluons. We shortly review the most common compositions of mesons, which are of interest for the understanding of low-lying meson resonances, namely, the ordinary quark-antiquark states as well as the nonordinary glueball, tetraquark, and other states. We dedicate special attention to Jaffe’s generalization of the tetraquark with $N_c-1$ $q\overline{q}$ pairs, which is the only type of state we have identified whose width does not necessarily vanish with $N_c$, though it does decouple exponentially with $N_c$ from the $\pi \pi$ channel, so that it is weakly coupled to the meson-meson system.

We precisely derive the mass squared matrices for charged and neutral (CP-odd and CP-even) Higgs, as well as the mass matrices for neutrino-neutralino and charged lepton-chargino in the minimal $R$-parity violating supersymmetry with local $U(1{)}_{B-L}$ symmetry. In the framework the nonzero TeV scale vacuum expectations of right-handed sneutrinos induce the heavy mass of neutral $U(1{)}_{B-L}$ gauge bosons and result in relatively large mixing between the lightest CP-even Higgs and the right-handed sneutrinos when we include the one-loop corrections to the scalar potential. We numerically show that there is parameter space of the considered model to accommodate experimental data on the new ones of Higgs signal from the LHC and experimental observations on the neutrino oscillation simultaneously.

Field theories in black hole spacetimes undergo dimensional reduction near horizon (in the Rindler limit) to two-dimensional conformal field theories. We investigate this enhancement of symmetries in the context of gauge/gravity duality by considering Rindler space as the boundary of anti-de Sitter space in three spacetime dimensions. We show that the loxodromy conjugacy class of the SO(2,2) isometry group is responsible for generating the special conformal transformations on the boundary under renormalization group flow. We use this approach to present an alternative derivation of the two-point function in Rindler space using AdS/CFT correspondence.

We investigate a simple extra-dimensional model and its four-dimensional vacua. This model has a two-form flux and a positive cosmological constant, and the extra dimensions are compactified as the product of $N$ two-spheres. The theory is an interesting laboratory because it is at once simple enough to be soluble but rich enough to exhibit many features not present in previous model landscapes.

In this paper, we consider the finite-temperature behavior of the $CPT$-even aether-like Lorentz-breaking term in the extended Lorentz-breaking QED and demonstrate that its ambiguities, whose presence has been shown earlier in the zero-temperature case, stay also at a finite temperature.

To find more deliberate $f(R,T)$ cosmological solutions, we take our previous paper further by studying some new aspects of the considered models via investigation of some new cosmological parameters/quantities to attain the most acceptable cosmological results. Our investigations are performed by applying the dynamical system approach. We obtain the cosmological parameters/quantities in terms of some defined dimensionless parameters that are used in constructing the dynamical equations of motion. The investigated parameters/quantities are the evolution of the Hubble parameter and its inverse, the “weight function”; the ratio of the matter density to the dark energy density and its time variation; the deceleration; the jerk and the snap parameters; and the equation-of-state parameter of the dark energy. We numerically examine these quantities for two general models $R+\alpha R^{-n}+\sqrt{-T}$ and $R\log {[\alpha R]}^q+\sqrt{-T}$. All considered models have some inconsistent quantities (with respect to the available observational data), except the model with $n=-0.9$, which has more consistent quantities than the other ones. By considering the ratio of the matter density to the dark energy density, we find that the coincidence problem does not refer to a unique cosmological event; rather, this coincidence also occurred in the early Universe. We also present the cosmological solutions for an interesting model $R+c_1\sqrt{-T}$ in the nonflat Friedmann–Lemaître–Robertson–Walker metric. We show that this model has an attractor solution for the late times, though with $w^{(\mathrm{DE})}=-1/2$. This model indicates that the spatial curvature density parameter gets negligible values until the present era, in which it acquires the values of the order ${10}^{-4}$ or ${10}^{-3}$. As the second part of this work, we consider the weak-field limit of $f(R,T)$ gravity models outside a spherical mass immersed in the cosmological fluid. We have found that the corresponding field equations depend on the both background values of the Ricci scalar and the background cosmological fluid density. As a result, we attain the parametrized post-Newtonian parameter for $f(R,T)$ gravity and show that this theory can admit the experimentally acceptable values of this parameter. As a sample, we present the post-Newtonian gamma parameter for general minimal power law models, in particular, the model $R+c_1\sqrt{-T}$.

We discuss in detail a particularly simple example of a bimetric massive gravity model which seems to offer an alternative to the standard cosmological model at background level. For small redshifts, its equation of state is $w(z)\approx -1.22_{-0.02}^{+0.02}-0.64_{-0.04}^{+0.05}z/(1+z)$. Just like $\mathrm{\Lambda }\mathrm{CDM}$, it depends on a single parameter, has an analytical background expansion law and fits the expansion cosmological data well. However, confirming previous results, we find that the model is unstable at early times at small scales and speculate over possible ways to cure the instability. In the regime in which the model is stable, we find that it fits the linear perturbation observations well and has a growth index of approximately $\gamma =0.47$.

We study charged-fluid toroidal structures surrounding a nonrotating charged black hole immersed in a large-scale, asymptotically uniform magnetic field. In continuation of our former study on electrically charged matter in approximation of zero conductivity, we demonstrate the existence of orbiting structures in permanent rigid rotation in the equatorial plane and charged clouds hovering near the symmetry axis. We constrain the range of parameters that allow stable configurations and derive the geometrical shape of equipressure surfaces. Our simplified analytical study suggests that these regions of stability may be relevant for trapping electrically charged particles and dust grains in some areas of the black hole magnetosphere and thus important in some astrophysical situations.

We calculate the kick generated by an eccentric black hole binary inspiral as it evolves through a resonant orbital configuration where the precession of the system temporarily halts. As a result, the effects of the asymmetric emission of gravitational waves build up coherently over a large number of orbits. Our results are calculated using black hole perturbation theory in the limit where the ratio of the masses of the orbiting objects $\epsilon =m/M$ is small. The resulting kick velocity scales as ${\epsilon }^{3/2}$, much faster than the ${\epsilon }^2$ scaling of the kick generated by the final merger. For the most extreme case of a very eccentric ($e\sim 1$) inspiral around a maximally spinning black hole, we find kicks close to $30000{\epsilon }^{3/2}\mathrm{km}/\mathrm{s}$, enough to dislodge an intermediate-mass black hole from its host globular cluster. In reality, such extreme inspirals should be very rare. Nonetheless, the astrophysical impact of kicks in less extreme inspirals could be astrophysically significant.

We prove that the $z=1$ and $z=3$ Lifshitz black hole solutions of new massive gravity in three dimensions are the only static axisymmetric solutions that can be cast in a Kerr-Schild form with a seed metric given by the Lifshitz spacetime. Correspondingly, we study the issue of uniqueness of Lifshitz solitons when considering an ansatz involving a single metric function. We show this problem can be mapped to the previous one and that the $z=1$ and $z=1/3$ Lifshitz soliton solutions are the only ones within this class. Finally, our approach suggests for the first time an explanation as to what is special about those particular values of the dynamical critical exponent $z$ at finite temperature.

In this paper we present the post-Newtonian (pN) coefficients of the energy flux (and angular momentum flux) at infinity and event horizon for a particle in circular, equatorial orbits about a Kerr black hole (of mass $M$ and spin-parameter $a$) up to 20-pN order. When a pN term is not a polynomial in $a/M$ and includes irrational functions (like polygamma functions), it is written as a power series of $a/M$. This is achieved by calculating the fluxes numerically with an accuracy greater than 1 part in ${10}^{600}$, using the methods outlined in Sasaki and Tagoshi [Living Rev. Relativity 6, 6 (2003); Tagoshi et al., Prog. Theor. Phys. 98, 829 (1997)]. Such high accuracy allows us to extract analytical values of pN coefficients that are linear combinations of transcendentals like the Euler constant, logarithms of prime numbers, and powers of $\pi$. We also present the 22-pN expansion (spin-independent pN expansion) of the ingoing energy flux at the event horizon for a particle in circular orbit about a Schwarzschild black hole.

We present a general method to reconstruct static spherically symmetric metrics in general relativity based on the $1+1+2$ covariant approach. This method allows a more complete exploration of the properties of these metrics in the case of a generic fluid and in the presence of a scalar field. A number of new exact solutions are reconstructed in these cases.

We present a new, tunable effective-one-body (EOB) model of the motion and radiation of coalescing black-hole binaries with arbitrary mass ratio and aligned spins. The most novel feature of our formalism is the introduction, and systematic use, of the (gauge-invariant) concept of centrifugal radius $r_c$. In the spinning small mass-ratio limit, the main radial potential expressed in terms of $r_c$ differs very little (and only multiplicatively so) from the usual Schwarzschild potential $1–2M/r_c$. This motivates a new, multiplicative way of blending finite-mass-ratio deformations with spin deformations. In the present exploratory work we consider a minimal version of our spinning EOB model (containing essentially only two adjustable parameters: one in the Hamiltonian and one in the waveform) and calibrate its (dominant mode) waveform against a sample of fifteen equal-mass, equal-spin waveforms produced by the SXS Collaboration, and covering the dimensionless spin range $-0.95\le \chi \le +0.98$. The numerical relativity/EOB phasing disagreement remains remarkably small ($\lesssim \pm 0.15\mathrm{rad}$) over the entire spin range.