In the present paper we study the semileptonic decays of ${\overline{B}}_s$ mesons in the context of nonrelativistic Constituent Quark Models. We estimate the uncertainties of our calculation using different interquark potentials to obtain the meson wave functions. We check the results from our model against the predictions of heavy quark symmetry, in the limit of infinite heavy quark mass. We also study the nonleptonic decays of ${\overline{B}}_s$ mesons within the factorization approximation.

The successful miniaturization of extremely accurate atomic clocks invites prospects for satellite missions to perform precise timing experiments. This will allow effects predicted by general relativity to be detected in Earth’s gravitational field. In this paper we introduce a convenient formalism for studying these effects, and compute the fractional timing differences generated by them for the orbit of a satellite capable of accurate time transfer to a terrestrial receiving station on Earth, as proposed by planned missions. We find that (1) Schwarzschild perturbations will be measurable through their effects both on the orbit and on the signal propagation, (2) frame-dragging of the orbit will be readily measurable, and (3) in optimistic scenarios, the spin-squared metric effects may be measurable for the first time ever. Our estimates suggest that a clock with a fractional timing inaccuracy of ${10}^{-16}$ on a highly eccentric Earth orbit will measure all these effects, while for a low Earth circular orbit like that of the Atomic Clock Ensemble in Space mission, detection will be more challenging.

For a stationary and axisymmetric black hole, there is a natural way to split the fields into a probe sector and a background sector. The equations of motion for the probe sector enjoy a significantly enhanced symmetry on the black hole horizon. The extended symmetry is conformal in four dimensions, while in higher dimensions it is much bigger. This puts conformal symmetry at the bottom of the ladder of symmetries that can arise on black hole horizons in generic dimensions.

We investigate the consequences of throwing point particles into odd-dimensional Myers-Perry black holes in asymptotically anti–de Sitter (AdS) backgrounds. We restrict our attention to the case in which the angular momenta of the background geometry are all equal. This process allows us to test the generalization of the weak cosmic censorship conjecture to asymptotically AdS spacetimes in higher dimensions. We find no evidence for overspinning in $D=5,7,9$ and 11 dimensions. Instead, test particles carrying the maximum possible angular momentum that still fall into an extremal rotating black hole generate a flow along the curve of extremal solutions.

Distance measurements are usually thought to probe the “background” metric of the Universe, but in reality the presence of perturbations will lead to deviations from the result expected in an exactly homogeneous and isotropic universe. At least in principle the presence of perturbations could even explain the observed distance-redshift relation without the need for dark energy. In this paper we reinvestigate a toy model where perturbations are plane symmetric, and for which exact solutions are known in the fluid limit. However, if perturbations are large, shell crossing occurs and the fluid approximation breaks down. This prevents the study of the most interesting cases. Here we use a general-relativistic $N$-body simulation that does not suffer from this problem and which allows us to go beyond previous works. We show that even for very large plane symmetric perturbations we are not able to mimic the observed distance-redshift relation. We also discuss how the synchronous comoving gauge breaks down when shell crossing occurs, while metric perturbations in the longitudinal gauge remain small. For this reason the longitudinal (Newtonian) gauge appears superior for relativistic $N$-body simulations of large-scale structure formation.

We investigate the possibility for classical metric signature change in a straightforward generalization of the first-order formulation of gravity, dubbed “Cartan gravity.” The mathematical structure of this theory mimics the electroweak theory in that the basic ingredients are an $SO(1,4)$ Yang-Mills gauge field ${A^{ab}}_{\mu }$ and a symmetry breaking Higgs field $V^a$, with no metric or affine structure of spacetime presupposed. However, these structures can be recovered, with the predictions of general relativity exactly reproduced, whenever the Higgs field breaking the symmetry to $SO(1,3)$ is forced to have a constant (positive) norm $V^a{V}_a$. This restriction is usually imposed “by hand,” but in analogy with the electroweak theory we promote the gravitational Higgs field $V^a$ to a genuine dynamical field, subject to nontrivial equations of motion. Even though we limit ourselves to actions polynomial in these variables, we discover a rich phenomenology. Most notably we derive classical cosmological solutions exhibiting a smooth transition between Euclidean and Lorentzian signature in the four-metric. These solutions are nonsingular and arise whenever the $SO(1,4)$ norm of the Higgs field changes sign; i.e. the signature of the metric of spacetime is determined dynamically by the gravitational Higgs field. It is possible to find a plethora of such solutions and in some of them this dramatic behavior is confined to the early Universe, with the theory asymptotically tending to Einstein gravity at late times. Curiously the theory can also naturally embody a well-known dark energy model: Peebles-Ratra quintessence.

Recently, a combined model of the primordial inflation and the present cosmic acceleration has been proposed in the context of $f(R)$ gravity. This model is composed of the late-time acceleration term and an $R^2$ term, which enables the model to avoid high curvature singularity and describe a quasi–de Sitter inflationary phase in the early universe. An interesting feature of this model is that the reheating dynamics after the inflation is significantly modified, in contrast to the original $R^2$ model, and affects the shape of a gravitational-wave background (GWB) spectrum. Here we investigate the production of a GWB during the inflation and reheating eras in the $R^2$-corrected $f(R)$ model and compute a GWB spectrum. We found that an interesting region of the model parameters has already been excluded by the cosmological limit on the abundance of GWs.

We investigate the growth of the large-scale structure in the superfluid Chaplygin gas (SCG) model. Both linear and nonlinear growth, such as ${\sigma }_8$ and the skewness $S_3$, are discussed. We find the growth factor of SCG reduces to the Einstein–de Sitter case at early times while it differs from the cosmological constant model ($\mathrm{\Lambda }\mathrm{CDM}$) case in the large $a$ limit. We also find there will be more stricture growth on large scales in the SCG scenario than in $\mathrm{\Lambda }\mathrm{CDM}$ and the variations of ${\sigma }_8$ and $S_3$ between SCG and $\mathrm{\Lambda }\mathrm{CDM}$ cannot be discriminated.

We consider enhancing the sensitivity of future gravitational-wave detectors by adding optical filters inside the signal-recycling cavity—an intracavity filtering scheme, which coherently feeds the sideband signal back to the interferometer with a proper frequency-dependent phase. We study three cases of such a scheme with different motivations: (i) the case of backaction noise evasion, trying to cancel radiation-pressure noise with only one filter cavity for a signal-recycled interferometer; (ii) the speed-meter case, similar to the speed-meter scheme proposed by Purdue and Chen [Phys. Rev. D 66, 122004 (2002)] but without the resonant-sideband-extraction mirror, and also relieves the optical requirement on the sloshing mirror; (iii) the broadband detection case with squeezed-light input, numerically optimized for a broadband sensitivity.

Targeted searches of continuous waves from spinning neutron stars normally assume that the frequency of the gravitational wave signal is at a given known ratio with respect to the rotational frequency of the source, e.g., twice for an asymmetric neutron star rotating around a principal axis of inertia. In fact this assumption may well be invalid if, for instance, the gravitational wave signal is due to a solid core rotating at a slightly different rate with respect to the star crust. In this paper we present a method for narrow-band searches of continuous gravitational wave signals from known pulsars in the data of interferometric detectors. This method assumes source position is known to high accuracy, while a small frequency and spin-down range around the electromagnetic-inferred values is explored. Barycentric and spin-down corrections are done with an efficient time-domain procedure. Sensitivity and computational efficiency estimates are given and results of tests done using simulated data are also discussed.

The Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov, Kovner Hamiltonian for high energy evolution of QCD amplitudes is presented at the next-to-leading order accuracy in ${\alpha }_s$. The form of the Hamiltonian is deduced from the symmetries and the structure of the hadronic light cone wavefunction and by comparing the rapidity evolution of the quark dipole and the three-quark singlet states with results available in the literature. The next-to-leading corrections should allow for more robust phenomenological applications of perturbative saturation approach.

The isospin violation process $Y(4260)\to J/\psi \eta {\pi }^0$ is studied assuming that $Y(4260)$ is a $D_1\overline{D}+c.c$. hadronic molecule. In association with the production of the $Z_c(3900)$, which is treated as a $D{\overline{D}}^{*}+c.c$. hadronic molecule, this process can help us distinguish the molecular nature of $Y(4260)$ from other scenarios since the incomplete cancellation between the charged and neutral-meson loops, which are prominent in the molecular picture only, produces a peak in the $e^{+}{e}^{-}\to Y(4260)\to J/\psi \eta {\pi }^0$ cross section at the $D_1\overline{D}+c.c$. threshold and a very prominent peak in the $J/\psi \eta$ invariant mass spectrum in between the $D{\overline{D}}^{*}+c.c$. thresholds, the latter being much narrower than the corresponding one in the isospin conserving channel, i.e. $J/\psi {\pi }^{+}{\pi }^{-}$. The partial width of $Y(4260)\to J/\psi \eta {\pi }^0$ is about $4\times {10}^{-4}$ times that of $Y(4260)\to J/\psi {\pi }^{+}{\pi }^{-}$. The cross section of $e^{+}{e}^{-}\to Y(4260)\to J/\psi \eta {\pi }^0$ at the $D_1\overline{D}+c.c$. threshold is about 0.05 pb, which is much larger than that produced by the nearby resonances. These features are the direct consequence of the assumed nature of these two states, especially for the $Y(4260)$, which might be accessible at high-statistics experiments such as BESIII and LHCb.

We compute the two-loop fermion self-energy in massless reduced quantum electrodynamics (RQED) for an arbitrary gauge in the case where the photon field is three dimensional and the fermion field is two dimensional: super-renormalizable ${\mathrm{RQED}}_{3,2}$ with $N_F$ fermions. We find that the theory is infrared finite at two-loop and that finite corrections to the fermion propagator have a remarkably simple form.

We compute the direct-current resistivity of a scale-invariant, $d$-dimensional strange metal with dynamic critical exponent $z$ and hyperscaling-violating exponent $\theta$, weakly perturbed by a scalar operator coupled to random-field disorder that locally breaks a ${\mathbb{Z}}_2$ symmetry. Independent calculations via Einstein-Maxwell dilaton holography and memory matrix methods lead to the same results. We show that random-field disorder has a strong effect on resistivity and leads to a short relaxation time for the total momentum. In the course of our holographic calculation, we use a nontrivial dilaton coupling to the disordered scalar, allowing us to study a strongly coupled scale-invariant theory with $\theta \ne 0$. Using holography, we are also able to determine the disorder strength at which perturbation theory breaks down. Curiously, for locally critical theories, this breakdown occurs when the resistivity is proportional to the entropy density, up to a possible logarithmic correction.

We examine the RG flow of a candidate $c$ function, extracted from the holographic entanglement entropy of a strip-shaped region, for theories with broken Lorentz invariance. We clarify the conditions on the geometry that lead to a breakdown of monotonic RG flows as is expected for generic Lorentz-violating field theories. Nevertheless we identify a set of simple criteria on the UV behavior of the geometry which guarantee a monotonic $c$ function. Our analysis can thus be used as a guiding principle for the construction of monotonic RG trajectories and can also prove useful for excluding possible IR behaviors of the theory.

We continue our study on the partition function for 5D supersymmetric Yang-Mills theory on toric Sasaki-Einstein $Y^{p,q}$ manifolds. Previously, using the localization technique, we have computed the perturbative part of the partition function. In this work we show how the perturbative part factorizes into four pieces, each corresponding to the perturbative answer of the same theory on ${\mathbb{R}}^4\times S^1$. This allows us to identify the equivariant parameters and to conjecture the full partition functions (including the instanton contributions) for $Y^{p,q}$ spaces. The conjectured partition function receives contributions only from singular contact instantons supported along the closed Reeb orbits. At the moment we are not able to prove this fact from the first principles.

In this work we present an approach that can be systematically used to construct nonlinear systems possessing analytical multikink profile configurations. In contrast with previous approaches to the problem, we are able to do it by using field potentials that are considerably smoother than the ones of the doubly quadratic family of potentials. This is done without losing the capacity of writing exact analytical solutions. The resulting field configurations can be applied to the study of problems from condensed matter to braneworld scenarios.

We compute the two-loop fermion self-energy in massless reduced quantum electrodynamics for an arbitrary gauge using the method of integration by parts. Focusing on the limit where the photon field is four-dimensional, our formula involves only recursively one-loop integrals and can therefore be evaluated exactly. From this formula, we deduce the anomalous scaling dimension of the fermion field as well as the renormalized fermion propagator up to two loops. The results are then applied to the ultrarelativistic limit of graphene and compared with similar results obtained for four-dimensional and three-dimensional quantum electrodynamics.

We study and compare the spectra of geometric operators (length and area) in the quantum kinematics of two formulations of three-dimensional Lorentzian loop quantum gravity. In the $\mathrm{SU}(2)$ Ashtekar-Barbero framework, the spectra are discrete and depend on the Barbero-Immirzi parameter $\gamma$ exactly like in the four-dimensional case. However, we show that when working with the self-dual variables and imposing the reality conditions the spectra become continuous and $\gamma$ independent.