We present an estimate of the partial width of $X(3872)$ into $p\overline{p}$ under the assumption that it is a weakly bound hadronic molecule whose constituents are a superposition of the charm mesons $D^{*0}{\overline{D}}^0$ and $D^0{\overline{D}}^{*0}$. The $p\overline{p}$ partial width of $X$ is therefore related to the cross section for $p\overline{p}\to D^{*0}{\overline{D}}^0$ near the threshold. That cross section at an energy well above the threshold is estimated by scaling the measured cross section for $p\overline{p}\to K^{*-}{K}^{+}$. It is extrapolated to the $D^{*0}{\overline{D}}^0$ threshold by taking into account the threshold resonance in the $1^{++}$ channel. The resulting prediction for the $p\overline{p}$ partial width of $X(3872)$ is proportional to the square root of its binding energy. For the current central value of the binding energy, the estimated partial width into $p\overline{p}$ is comparable to that of the P-wave charmonium state ${\chi }_{c1}$.

We reexamine constraints from the recent evidence for observation of the lifetime difference in $D^0\mathrm{\text{−}}{\overline{D}}^0$ mixing on the parameters of supersymmetric models with $R$-parity violation (RPV). We find that RPV supersymmetry can give large negative contribution to the lifetime difference. We also discuss the importance of the choice of weak or mass basis when placing the constraints on RPV-violating couplings from flavor mixing experiments.

We evaluate the radiative decay into a pseudoscalar meson and a photon of the whole set of the axial-vector mesons dynamically generated from the vector-pseudoscalar meson interaction. We take into account tree level and loop diagrams coming from the axial-vector decay into a vector and a pseudoscalar meson. We find a large span for the values of the radiative widths of the different axial-vector mesons. In particular, we evaluate the radiative decay into $K\gamma$ of the two $K_1(1270)$ states, recently claimed theoretically, and discuss the experimental values quoted so far on the assumption of only one state.

The atmospheric neutrino background for proton decay via $p\to e^{+}{\pi }^0$ in ring imaging water Cherenkov detectors is studied with an artificial accelerator neutrino beam for the first time. In total, $3.14\times {10}^5$ neutrino events corresponding to about 10 megaton-years of atmospheric neutrino interactions were collected by a 1000 ton water Cherenkov detector (KT). The KT charged-current single ${\pi }^0$ production data are well reproduced by simulation programs of neutrino and secondary hadronic interactions used in the Super-Kamiokande (SK) proton decay search. The obtained $p\to e^{+}{\pi }^0$ background rate by the KT data for SK from the atmospheric neutrinos whose energies are below 3 GeV is ${1.63}_{-0.33}^{+0.42}(\mathrm{stat}{)}_{-0.51}^{+0.45}(\mathrm{syst})(\mathrm{megaton}\mathrm{\text{−}}\mathrm{year}{)}^{-1}$. This result is also relevant to possible future, megaton-scale water Cherenkov detectors.

A Vaidya-based model of a radiating black hole is studied in a 5-dimensional Einstein gravity with Gauss-Bonnet contribution of quadratic curvature terms. The structure and locations of the apparent and event horizons of the radiating black hole are determined.

In theories with a large number $N$ of particle species, black hole physics imposes an upper bound on the mass of the species equal to $M_{\mathrm{Planck}}/\sqrt{N}$. This bound suggests a novel solution to the hierarchy problem in which there are $N\approx {10}^{32}$ gravitationally coupled species, for example ${10}^{32}$ copies of the standard model. The black hole bound forces them to be at the weak scale, hence providing a stable hierarchy. We present various arguments, that in such theories the effective gravitational cutoff is reduced to ${\Lambda }_G\approx M_{\mathrm{Planck}}/\sqrt{N}$ and a new description is needed around this scale. In particular, black holes smaller than ${\Lambda }_G^{-1}$ are already no longer semiclassical. The nature of the completion is model dependent. One natural possibility is that ${\Lambda }_G$ is the quantum gravity scale. We provide evidence that within this type of scenarios, contrary to the standard intuition, micro-black-holes have a (slowly fading) memory of the species of origin. Consequently, the black holes produced at LHC will predominantly decay into the standard model particles, and negligibly into the other species.

We propose a unified superfield formulation of $N=4$ off-shell supermultiplets in one spacetime dimension using the standard $N=4$ superspace. The main idea of our approach is a gluing together of two linear supermultiplets along their fermions. The functions defining such a gluing obey a system of equations. Each solution of this system provides a new supermultiplet, linear or nonlinear, modulo equivalence transformations. In such a way we reproduce all known linear and nonlinear $N=4$, $d=1$ supermultiplets and propose some new ones. Particularly interesting is an explicit construction of nonlinear $N=4$ hypermultiplets.

Standard choices of quasicircular orbit parameters for black-hole binary evolutions result in eccentric inspiral. We introduce a conceptually simple method, which is to integrate the post-Newtonian equations of motion through hundreds of orbits, and read off the values of the momenta at the separation at which we wish to start a fully general relativistic numerical evolution. For the particular case of nonspinning equal-mass inspiral with an initial coordinate separation of $D=11M$ we show that this approach reduces the eccentricity by at least a factor of 5 to $e<0.002$ as compared to using standard quasicircular initial parameters.

We consider pion electroproduction close to threshold for $Q^2$ in the region $1–10{\mathrm{GeV}}^2$ on a nucleon target. The momentum transfer dependence of the S-wave multipoles at threshold, $E_{0+}$ and $L_{0+}$, is calculated in the chiral limit using light-cone sum rules. Predictions for the cross sections in the threshold region are given taking into account P-wave contributions that, as we argue, are model independent to a large extent. The results are compared with the SLAC E136 data on the structure function $F_2(W,Q^2)$ in the threshold region.

We study the color-dependent confining forces between two quarks by the quenched lattice simulations of Coulomb gauge QCD. The color-singlet and color-antitriplet instantaneous potentials yield attractive forces. The ratio of the string tensions obtained from them is approximately 2, and these tensions have little volume dependence. Meanwhile, the color-octet and color-sextet channels give a minor contribution to the two-quark system. We finally find that the infrared self-energy of the color-nonsinglet channels diverges in the infinite volume limit; however, the degree of the divergence on the finite lattice can be understood in terms of color factors.

Using the framework of quantum field theory in curved spacetime, I analyze the synchrotron scalar radiation emitted by a source orbiting a Schwarzschild black hole in both stable and unstable circular orbits. The comparison between the emitted power in Schwarzschild spacetime and the one obtained in Minkowski spacetime assuming Newtonian gravitation is performed. The amount of the emitted radiation which is absorbed by the black hole is also computed.

The variational method within the Hamiltonian formalism of quantum field theory is used to derive relativistic $n$-body wave equations for scalar particles and antiparticles. The equations are shown to have the Schrödinger nonrelativistic limit, with Coulombic interparticle potentials in the case of a massless mediating field and Yukawa interparticle potentials in the case of a massive mediating field. Approximate ground state solutions for the particular case of a five-body system are obtained for various strengths of coupling, for both massive and massless mediating fields. The binding energy of a five-body system is studied, particularly at strong coupling, for different cases where the virtual annihilation interactions and retardation effects in the wave equations are included or excluded.

We extend our previous studies of head-on collisions of boson stars by considering orbiting binary boson stars. We concentrate on equal-mass binaries and study the dynamical behavior of boson/boson and boson/antiboson pairs. We examine the gravitational wave output of these binaries and compare with other compact binaries. Such a comparison lets us probe the apparent simplicity observed in gravitational waves produced by black hole binary systems. In our system of interest however, there is an additional internal freedom which plays a significant role in the system’s dynamics, namely, the phase of each star. Our evolutions show rather simple behavior at early times, but large differences occur at late times for the various initial configurations.

Belinskii, Khalatnikov, and Lifshitz (BKL) conjectured that the description of the asymptotic behavior of a generic solution of Einstein equations near a spacelike singularity could be drastically simplified by considering that the time derivatives of the metric asymptotically dominate (except at a sequence of instants, in the “chaotic case”) over the spatial derivatives. We present a precise formulation of the BKL conjecture (in the chaotic case) that consists of basically three elements: (i) we parametrize the spatial metric $g_{ij}$ by means of Iwasawa variables $({\beta }^a,\mathcal{N}^a{}_i)$; (ii) we define, at each spatial point, a (chaotic) asymptotic evolution system made of ordinary differential equations for the Iwasawa variables; and (iii) we characterize the exact Einstein solutions $\beta$, $\mathcal{N}$ whose asymptotic behavior is described by a solution ${\beta }_{[0]}$, ${\mathcal{N}}_{[0]}$ of the previous evolution system by means of a “generalized Fuchsian system” for the differenced variables $\overline{\beta }=\beta -{\beta }_{[0]}$, $\overline{\mathcal{N}}=\mathcal{N}-{\mathcal{N}}_{[0]}$, and by requiring that $\overline{\beta }$ and $\overline{\mathcal{N}}$ tend to zero on the singularity. We also show that, in spite of the apparently chaotic infinite succession of “Kasner epochs” near the singularity, there exists a well-defined asymptotic geometrical structure on the singularity: it is described by a partially framed flag. Our treatment encompasses Einstein-matter systems (comprising scalar and $p$-forms), and also shows how the use of Iwasawa variables can simplify the usual (“asymptotically velocity term dominated”) description of nonchaotic systems.

Thermal noise is expected to be the dominant source of noise in the most sensitive frequency band of second-generation, ground-based gravitational-wave detectors. Reshaping the beam to a flatter, wider profile which probes more of the mirror surface reduces this noise. The “Mesa” beam shape has been proposed for this purpose and was subsequently generalized to a family of hyperboloidal beams with two parameters: twist angle $\alpha$ and beam width $D$. Varying $\alpha$ allows a continuous transition from the nearly flat ($\alpha =0$) to the nearly concentric ($\alpha =\pi$) Mesa beam configurations. We analytically prove that in the limit $D\to \infty$ hyperboloidal beams become Gaussians. The ideal beam choice for reducing thermal noise is the widest possible beam that satisfies the Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) diffraction loss design constraint of 1 part per million (ppm) per bounce for a mirror radius of 17 cm. In the past the diffraction loss has often been calculated using the clipping approximation that, in general, underestimates the diffraction loss. We develop a code using pseudospectral methods to compute the diffraction loss directly from the propagator. We find that the diffraction loss is not a strictly monotonic function of beam width, but has local minima that occur due to finite mirror effects and leads to natural choices of $D$. For an $\alpha =\pi$ Mesa beam a local minimum occurs at $D=10.67\mathrm{cm}$ and leads to a diffraction loss of 1.4 ppm. We then compute the thermal noise for the entire hyperboloidal family. We find that if one requires a diffraction loss of strictly 1 ppm, the $\alpha =0.91\pi$ hyperboloidal beam is optimal, leading to the coating thermal noise (the dominant source of noise for fused-silica mirrors) being lower by about 10% than for a Mesa beam while other types of thermal noise decrease as well. We then develop an iterative process that reconstructs the mirror to specifically account for finite mirror effects. This allows us to increase the $D$ parameter to 11.35 cm for a nearly concentric Mesa beam and lower the coating noise by about 30% compared to the original Mesa configuration.

We compute nonequilibrium dynamics for classical-statistical SU(2) pure gauge theory on a lattice. We consider anisotropic initial conditions with high occupation numbers in the transverse plane on a characteristic scale $\sim Q_s$. This is used to investigate the very early stages of the thermalization process in the context of heavy-ion collisions. We find Weibel or primary instabilities with growth rates similar to those obtained from previous treatments employing anisotropic distributions of hard modes (particles) in the weak coupling limit. We observe secondary growth rates for higher-momentum modes reaching substantially larger values and we analyze them in terms of resummed loop diagrams beyond the hard-loop approximation. We find that a coarse-grained pressure isotropizes “bottom-up” with a characteristic inverse rate of ${\gamma }^{-1}\simeq 1–2\mathrm{fm}/\mathrm{c}$ for coarse-graining momentum scales of $p\lesssim 1\mathrm{GeV}$ choosing an initial energy density for RHIC of $ϵ=30\mathrm{GeV}/{\mathrm{fm}}^3$. The nonequilibrium spatial Wilson loop is found to exhibit an area law and to become isotropic on a similar time scale.

We present the gluon-gluon and photon-gluon helicity amplitudes for color singlet and octet charmonium production in polarized and unpolarized hadron-hadron and photon-hadron collisions.

This is a reply to the preceding “Comment on ‘Noncommutative gauge theories and Lorentz symmetry,’” Phys. Rev. D 77, 048701 (2008) by Alfredo Iorio.

We show that Lorentz symmetry is generally absent for noncommutative (Abelian) gauge theories and obtain a compact formula for the divergence of the Noether currents that allows a thorough study of this instance of symmetry violation. We use that formula to explain why the results of “Noncommutative gauge theories and Lorentz symmetry”, Phys. Rev. D 70, 125004 (2004) by R. Banerjee, B. Chakraborty, and K. Kumar, interpreted there as new criteria for Lorentz invariance, are in fact just a particular case of the general expression for Lorentz violation obtained here. Finally, it is suggested that the divergence formula should hold in a vast class of cases, such as, for instance, the standard model extension.