Using data samples of $102\times {10}^6$ $\mathrm{\Upsilon }(1S)$ and $158\times {10}^6$ $\mathrm{\Upsilon }(2S)$ events collected with the Belle detector, a first experimental search has been made for double-charmonium production in the exclusive decays $\mathrm{\Upsilon }(1S,2S)\to J/\psi ({\psi }^{\prime })+X$, where $X={\eta }_c$, ${\chi }_{cJ}(J=0,1,2)$, ${\eta }_c(2S)$, $X(3940)$, and $X(4160)$. No significant signal is observed in the spectra of the mass recoiling against the reconstructed $J/\psi$ or ${\psi }^{\prime }$ except for the evidence of ${\chi }_{c1}$ production with a significance of $4.6\sigma$ for $\mathrm{\Upsilon }(1S)\to J/\psi +{\chi }_{c1}$. The measured branching fraction $\mathcal{B}(\mathrm{\Upsilon }(1S)\to J/\psi +{\chi }_{c1})$ is $[3.90\pm 1.21(\text{stat})\pm 0.23(\text{syst})]\times {10}^{-6}$. The 90% C.L. upper limits on the branching fractions of the other modes having a significance of less than $3\sigma$ are determined. These results are consistent with theoretical calculations using the nonrelativistic QCD factorization approach.

The creation of cold dark matter cosmology model is studied beyond the linear perturbation level. The skewness is explicitly computed, and the results are compared to those from the $\mathrm{\Lambda }\mathrm{CDM}$ model. It is explicitly shown that both models have the same signature for the skewness and cannot be distinguished by using this observable.

We study the pressure, $P$, of $\mathrm{SU}(N)$ gauge theory on a two-dimensional torus as a function of area, $A=l/t$. We find a crossover scale that separates the system on a large circle from a system on a small circle at any finite temperature. The crossover scale approaches zero with increasing $N$ and the crossover becomes a first-order transition as $N\to \infty$ and $l\to 0$ with the limiting value of $\frac{2Pl}{(N-1)t}$ depending on the fixed value of $Nl$.

Recently, several works have investigated the coupling to matter in ghost-free massive bigravity and multigravity and a new effective coupling to matter has been proposed. In this paper we clarify some confusion on the existence and the implications of a ghost above the strong coupling scale. We confirm that the standard constraint which is otherwise typically present in this type of theories disappears on generic backgrounds as soon as this new coupling is considered. This implies the reemergence of the Boulware-Deser ghost. Nevertheless the absence of ghost in the decoupling limit implies that the cutoff scale (if identified with the scale at which the ghost enters) is higher than the strong coupling scale. Therefore there is a valid interesting region of applicability for these couplings at scales below the cutoff.

We study properties of domain walls in the symmetron model, in which the scalar gravitational degree of freedom decouples from matter in regions of high density and exhibits a spontaneously broken $Z_2$ symmetry at low densities. The nonminimal coupling of the scalar to matter leads to a host of interesting properties of the domain walls that are not present in minimally coupled theories. We estimate the cosmological energy fraction in domain walls and find that this leads to an upper bound on the redshift of the symmetry breaking. We also show that a spherical symmetron wall can remain stable if it is “pinned” on matter halos and derive a criterion for the stability. In addition, we present results of numerical simulations of representative interactions between domain walls and matter overdensities.

Tidal coupling between members of a compact binary system can have an interesting and important influence on that binary’s dynamical inspiral. Tidal coupling also distorts the binary’s members, changing them (at lowest order) from spheres to ellipsoids. At least in the limit of fluid bodies and Newtonian gravity, there are simple connections between the geometry of the distorted ellipsoid and the impact of tides on the orbit’s evolution. In this paper, we develop tools for investigating tidal distortions of rapidly rotating black holes using techniques that are good for strong-field, fast-motion binary orbits. We use black hole perturbation theory, so our results assume extreme mass ratios. We develop tools to compute the distortion to a black hole’s curvature for any spin parameter, and for tidal fields arising from any bound orbit, in the frequency domain. We also develop tools to visualize the horizon’s distortion for black hole spin $a/M\le \sqrt{3}/2$ (leaving the more complicated $a/M>\sqrt{3}/2$ case to a future analysis). We then study how a Kerr black hole’s event horizon is distorted by a small body in a circular, equatorial orbit. We find that the connection between the geometry of tidal distortion and the orbit’s evolution is not as simple as in the Newtonian limit.

We study the occurrence of cuspy events on a light string stretched between two Y-junctions with fixed heavy strings. We first present an analytic study and give a solid criterion to discriminate between cuspy and noncuspy string configurations. We then describe a numerical code, built to test this analysis. Our numerical investigation allows us to look at the correlations between the string network’s parameters and the occurrence of cuspy phenomena. We show that the presence of large-amplitude waves on the light string leads to cuspy events. We then relate the occurrence of cuspy events to features like the number of vibration modes on the string or the string’s root-mean-square velocity.

A new charm-strange meson, the $D_{s1}^{*}(2863)$, has recently been observed by the LHCb Collaboration which also determined the $D_{sJ}^{*}(2860)$ to have spin 3. One of the speculations about the previously observed $D_{s1}^{*}(2710)$ is that it is the $1{{}^{3}D}_1(c\overline{s})$ state. In this paper we reexamine the quark model properties and assignments of these three states in light of these new measurements. We conclude that the $D_{s1}^{*}(2863)$ and $D_{s3}^{*}(2863)$ are the $1{{}^{3}D}_1(c\overline{s})$ and $1{{}^{3}D}_3(c\overline{s})$ states respectively and the $D_{s1}^{*}(2710)$ is the $2{{}^{3}S}_1(c\overline{s})$ state. In addition to these three states there are another three excited $D_s$ states in this mass region still to be found, the $2{{}^{1}S}_0$ and two $1D_2$ states. We calculate the properties of these states and expect that LHCb has the capability of observing these states in the near future.

We present a generalization of Lüscher’s relation between the finite-volume spectrum and scattering amplitudes to the case of three particles. We consider a relativistic scalar field theory in which the couplings are arbitrary aside from a ${\mathbb{Z}}_2$ symmetry that removes vertices with an odd number of particles. The theory is assumed to have two-particle phase shifts that are bounded by $\pi /2$ in the regime of elastic scattering. We determine the spectrum of the finite-volume theory from the poles in the odd-particle-number finite-volume correlator, which we analyze to all orders in perturbation theory. We show that it depends on the infinite-volume two-to-two K-matrix as well as a nonstandard infinite-volume three-to-three K-matrix. A key feature of our result is the need to subtract physical singularities in the three-to-three amplitude and thus deal with a divergence-free quantity. This allows our initial, formal result to be truncated to a finite dimensional determinant equation. At present, the relation of the three-to-three K-matrix to the corresponding scattering amplitude is not known, although previous results in the nonrelativistic limit suggest that such a relation exists.

We use Schwinger bosons as prepotentials for lattice gauge theory to define local linking operators and calculate their action on linking states for ($2+1$)-dimensional SU(2) lattice gauge theory. We develop a diagrammatic technique and associate a set of rules (lattice Feynman rules) to compute the entire loop dynamics diagrammatically. The physical loop space is shown to contain only nonintersecting loop configurations after solving the Mandelstam constraint. The smallest plaquette loops are contained in the physical loop space, and other configurations are generated by the action of a set of fusion operators on these basic loop states.

A new approach to computing the amplitudes of multiparticle processes in renormalizable quantum field theories is presented. Its major feature is a separation of the renormalization from the computation. Within the suggested approach, new computational rules are formulated. According to the new rules, the amplitudes under computation are expressed as a sum of effective Feynman amplitudes of which the vertices are the complete amplitudes of the processes involving not more than four particles, and the lines are the complete two-point functions. The new rules include prescriptions for computing the combinatorial factors by each amplitude. It is demonstrated that, due to these prescriptions, the combinatorial factors by the amplitudes that are divergent in the ultraviolet in four space-time dimensions vanish. Because of this, the computations within the new approach do not involve the ultraviolet renormalization.

In this paper we make a theoretical investigation of a new type of high-energy nonlinear Compton scattering phenomenon. In particular we show how, under certain conditions, interference effects arise when two laser pulses of different photon energy are shone upon a high-energy electron beam. The semiclassical operator method of Baier et al. is revisited as the method of investigation of this phenomenon. We show how their result can be cast into a form very similar to the classical result of radiation emission. Experimental verification of the described interference phenomenon is possible with current technology.

In this paper, we analyze a curvature- and torsion-square quantum gravity action with an additional Holst term minimally coupled to a massive Dirac field in four dimensions. The main purpose here is to try to estimate and compare the value of the Barbero-Immirzi parameter with its currently known results. To do that, we work out the physical mass of the fermion as a function of this parameter in a perturbative one-loop calculation, assuming the scenario of a physics at the TeV scale.

We investigate observational constraints on the Brans-Dicke cosmological model using observational data coming from distant supernovae type Ia, the Hubble function $H(z)$ measurements, information coming from the Alcock-Paczyński test, and baryon acoustic oscillations. Our analysis is based on the modified Friedmann function resulting form dynamical investigations of Brans-Dicke cosmology in the vicinity of a de Sitter state. The qualitative theory of dynamical systems enables us to obtain three different behaviors in the vicinity of this state. We find for a linear approach to the de Sitter state ${\omega }_{\mathrm{BD}}={-0.8606}_{-0.1341}^{+0.8281}$, for an oscillatory approach to the de Sitter state ${\omega }_{\mathrm{BD}}={-1.1103}_{-0.1729}^{+0.1872}$, and for the transient de Sitter state represented by a saddle-type critical point ${\omega }_{\mathrm{BD}}={-2.3837}_{-4.5459}^{+0.4588}$. We obtain the mass of the Brans-Dicke scalar field at the present epoch as $m_{\varphi }\sim H_0$. The Bayesian methods of model comparison are used to discriminate between obtained models. We show that observational data point toward vales of the ${\omega }_{\mathrm{BD}}$ parameter close to the value suggested by the low-energy limit of the bosonic string theory.

The bulk viscosity of cosmological fluid and the creation of cold dark matter both result in the generation of irreversible entropy (related to dissipative processes) in a homogeneous and isotropic universe. To consider such effects, the general cosmological equations are reformulated, focusing on a spatially flat matter-dominated universe. A phenomenological entropic-force model is examined that includes constant terms as a function of the dissipation rate ranging from $\tilde{\mu }=0$, corresponding to a nondissipative $\mathrm{\Lambda }\mathrm{CDM}$ (lambda cold dark matter) model, to $\tilde{\mu }=1$, corresponding to a fully dissipative CCDM (creation of cold dark matter) model. A time-evolution equation is derived for the matter density contrast in order to characterize density perturbations in the present entropic-force model. It is found that the dissipation rate affects the density perturbations even if the background evolution of the late universe is equivalent to that of a fine-tuned pure $\mathrm{\Lambda }\mathrm{CDM}$ model. With increasing dissipation rate $\tilde{\mu }$, the calculated growth rate for the clustering gradually deviates from observations, especially at low redshifts. However, the growth rate for low $\tilde{\mu }$ (less than 0.1) is found to agree well with measurements. A low-dissipation model predicts a smaller growth rate than does the pure $\mathrm{\Lambda }\mathrm{CDM}$ model (for which $\tilde{\mu }=0$). More detailed data are needed to distinguish the low-dissipation model from the pure $\mathrm{\Lambda }\mathrm{CDM}$ one.

Based on the multipoint propagator expansion, we present resummed perturbative calculations for cosmological power spectra and correlation functions in the context of modified gravity. In a wide class of modified gravity models that have a screening mechanism to recover general relativity (GR) on small scales, we apply the eikonal approximation to derive the governing equation for resummed propagator that partly includes the nonperturbative effect in the high-$k$ limit. The resultant propagator in the high-$k$ limit contains the new corrections arising from the screening mechanism as well as the standard exponential damping. We explicitly derive the expression for new high-$k$ contributions in specific modified gravity models, and find that in the case of $f(R)$ gravity for a currently constrained model parameter, the corrections are basically of the subleading order and can be neglected. Thus, in $f(R)$ gravity, similarly to the GR case, we can analytically construct the regularized propagator that reproduces both the resummed high-$k$ behavior and the low-$k$ results computed with standard perturbation theory, consistently taking account of the nonlinear modification of gravity valid at large scales. With the regularized multipoint propagators, we give predictions for power spectrum and correlation function at one-loop order, and compare those with $N$-body simulations in $f(R)$ gravity model. As an important application, we also discuss the redshift-space distortions and compute the anisotropic power spectra and correlation functions.

The Glashow resonance at $E_{\nu }=6.3\mathrm{PeV}$ is a measure of the ${\overline{\nu }}_e$ content of the astrophysical neutrino flux. The fractional ${\overline{\nu }}_e$ content depends on the neutrino production model at the cosmic neutrino source, and the environment at the source. Thus, the strength of the Glashow resonance event rate is a potential window into astrophysical sources. We quantify the “Glashow resonometer” and comment on the significance that no Glashow events are observed in the IceCube three-year data.

We study an SU(3) gauge theory with $N_f=8$ degenerate flavors of light fermions in the fundamental representation. Using the domain wall fermion formulation, we investigate the light hadron spectrum, chiral condensate $⟨\overline{\psi }\psi ⟩$ and electroweak $S$ parameter. We consider a range of light fermion masses on two lattice volumes at a single gauge coupling chosen so that IR scales approximately match those from our previous studies of the two- and six-flavor systems. Our results for the $N_f=8$ spectrum suggest spontaneous chiral symmetry breaking, though fits to the fermion mass dependence of spectral quantities do not strongly disfavor the hypothesis of mass-deformed infrared conformality. Compared to $N_f=2$ we observe a significant enhancement of $⟨\overline{\psi }\psi ⟩$ relative to the symmetry breaking scale $F$, similar to the situation for $N_f=6$. The reduction of the $S$ parameter, related to parity doubling in the vector and axial-vector channels, is also comparable to our six-flavor results.