We present the first numerical simulations of an initially nonspinning black-hole binary with mass ratio as large as $10:1$ in full general relativity. The binary completes approximately three orbits prior to merger and radiates $(0.415\pm 0.017)\%$ of the total energy and $(12.48\pm 0.62)\%$ of the initial angular momentum in the form of gravitational waves. The single black hole resulting from the merger acquires a kick of $(66.7\pm 3.3)\mathrm{km}/\mathrm{s}$ relative to the original center of mass frame. The resulting gravitational waveforms are used to validate existing formulas for the recoil, final spin, and radiated energy over a wider range of the symmetric mass ratio parameter $\eta =M_1{M}_2/(M_1+M_2{)}^2$ than previously possible. The contributions of $\ell >2$ multipoles are found to visibly influence the gravitational wave signal obtained at fixed inclination angles.

Based on a generalized uncertainty principle, Salecker-Wigner inequalities are modified. When applied to black holes, they give a modified black hole lifetime: $T_{\mathrm{MB}}\sim \frac{M^3}{m_p^3}(1-m_p^2/M^2)t_p$, and the number of bits required to specify the information content of the black hole as the event horizon area in Planck units $N\sim \frac{M^2}{m_p^2}(1-m_p^2/M^2)$.

We study the kinematics of timelike geodesic congruences in two and four dimensions in spacetime geometries representing stringy black holes. The Raychaudhuri equations for the kinematical quantities (namely, expansion, shear, and rotation) characterizing such geodesic flows are written down and subsequently solved analytically (in two dimensions) and numerically (in four dimensions) for specific geodesic flows. We compare between geodesic flows in dual (electric and magnetic) stringy black hole backgrounds in four dimensions, by showing the differences that arise in the corresponding evolutions of the kinematic variables. The crucial role of initial conditions and the spacetime curvature on the evolution of the kinematical variables is illustrated. Some novel general conclusions on caustic formation and geodesic focusing are obtained from the analytical and numerical findings. We also propose a new quantifier in terms of the time (affine parameter) of approach to a singularity, which may be used to distinguish between flows in different geometries. In summary, our quantitative findings bring out hitherto unknown features of the kinematics of geodesic flows, which, otherwise, would have remained overlooked, if we confined ourselves to only a qualitative analysis.

We study plasma effects on radiative transitions (e.g., decay of excited states of atoms or atomic nuclei) in a dense plasma at the transition frequencies $\omega \lesssim {\omega }_p$ (where ${\omega }_p$ is the electron plasma frequency). The decay goes through four channels—the emission of real transverse and longitudinal plasmons as well as the emission of virtual transverse and longitudinal plasmons with subsequent absorption of such plasmons by the plasma. The emission of real plasmons dies out at $\omega \le {\omega }_p$, but the processes with virtual plasmons strongly enhance the radiative decay. Applications of these results to radiative processes in white dwarf cores and neutron star envelopes are discussed.

In this paper we consider two models. First, we study tachyon-Gauss-Bonnet gravity and obtain the condition of the equation of state crossing $-1$. Second, we discuss the modified Gauss-Bonnet gravity with the tachyon field and show the condition of $\omega$ crossing $-1$. Also, we plot figures for $\omega$ numerically in special potential and coupling function.

In this paper, we study the effects of instrumental systematics on the reconstruction of the deflection angle power spectrum from weak lensing of cosmic microwave background (CMB) temperature and polarization observations. We consider 7 types of effects which are related to known instrumental systematics: calibration, rotation, pointing, spin-flip, monopole leakage, dipole leakage, and quadrupole leakage. These effects can result in the distortion in the CMB field and can be characterized by 11 distortion fields. Each of these systematic effects can mimic the effective projected matter power spectrum and hence contaminate the lensing reconstruction. To demonstrate the effect of these instrumental systematics on CMB lensing measurements, we consider two types of experiments: one with a detector noise level for polarization of $9.6\mu \mathrm{K}$ arcmin and FWHM of ${8.0}^{\prime }$, typical of upcoming ground and balloon-based CMB experiments; and a CMBPol-like instrument with a detector noise level for polarization of $2.0\mu \mathrm{K}$ arcmin and FWHM of ${4.0}^{\prime }$, typical of future space-based CMB experiments. For each systematics field, we consider various choices of coherence scale ${\alpha }_s$, starting from ${\alpha }_s={10}^{\prime }$ to the maximum of ${\alpha }_s={120}^{\prime }$. Among all the 11 systematic parameters, rotation $\omega$, and monopole leakage ${\gamma }_a$ & ${\gamma }_b$ place the most stringent requirements, while quadrupole leakage $q$, pointing error $p_a$ and $p_b$, and calibration $a$ are among the least demanding. The requirements from lensing extraction are about 1–2 orders of magnitude less stringent than the requirements to measure the primordial $B$ modes with an inflationary energy scale of $1.0\times {10}^{16}\mathrm{GeV}$. On the other hand, the requirements for lensing reconstruction are comparable or even more stringent for some systematic parameters than the requirements to detect primordial $B$ modes with an inflationary scale of $E_i=3.0\times {10}^{16}\mathrm{GeV}$.

We have searched for gravitational waves from coalescing low mass compact binary systems with a total mass between $2M_{\odot }$ and $35M_{\odot }$ and a minimum component mass of $1M_{\odot }$ using data from the first year of the fifth science run of the three LIGO detectors, operating at design sensitivity. Depending on the mass, we are sensitive to coalescences as far as 150 Mpc from the Earth. No gravitational-wave signals were observed above the expected background. Assuming a population of compact binary objects with a Gaussian mass distribution representing binary neutron star systems, black hole–neutron star binary systems, and binary black hole systems, we calculate the 90% confidence upper limit on the rate of coalescences to be $3.9\times {10}^{-2}{\mathrm{yr}}^{-1}{L}_{10}^{-1}$, $1.1\times {10}^{-2}{\mathrm{yr}}^{-1}{L}_{10}^{-1}$, and $2.5\times {10}^{-3}{\mathrm{yr}}^{-1}{L}_{10}^{-1}$, respectively, where $L_{10}$ is ${10}^{10}$ times the blue solar luminosity. We also set improved upper limits on the rate of compact binary coalescences per unit blue-light luminosity, as a function of mass.

Working within the theory of modified Gauss-Bonnet gravity, we show that Friedmann-Lemaître-Robertson-Walker–like power-law solutions only exist for a very special class of $f(\mathcal{G})$ theories. Furthermore, we point out that any transition from decelerated to accelerated expansion must pass through $\mathcal{G}=0$, and no function $f(\mathcal{G})$ that is differentiable at this point can admit both a decelerating power-law solution and any accelerating solution. This strongly constrains the cosmological viability of $f(\mathcal{G})$ gravity, since it may not be possible to obtain an expansion history of the Universe which is compatible with observations. We explain why the same issue does not occur in $f(R)$ gravity and discuss possible caveats for the case of $f(\mathcal{G})$ gravity.

We study the heavy quark effective theory prediction for semileptonic $B$ decays into an orbital excited $F$-wave charmed doublet, the $(2^{+},3^{+})$ states $(D_2^{{*}^{\prime }},D_3)$, at the leading order of heavy quark expansion. The corresponding universal form factor is estimated by using the QCD sum rule method. The decay rates we predict are ${\Gamma }_{B\to D_2^{{*}^{\prime }}\ell \overline{\nu }}=1.85\times {10}^{-19}\mathrm{GeV}$ and ${\Gamma }_{B\to D_3\ell \overline{\nu }}=1.78\times {10}^{-19}\mathrm{GeV}$. The branching ratios are $\mathcal{B}(B\to D_2^{{*}^{\prime }}\ell \overline{\nu })=4.6\times {10}^{-7}$ and $\mathcal{B}(B\to D_3\ell \overline{\nu })=4.4\times {10}^{-7}$, respectively.

The form factors of the semileptonic $B_c\to S(AV)\ell \nu$ ($\ell =\tau$, $\mu$, $e$) transitions, where $S$ and $AV$ denote the scalar $X_{c0}$ and axial-vector $(X_{c1},h_c)$ mesons, are calculated within the framework of the three-point QCD sum rules. The heavy quark effective theory limit of the form factors is also obtained and compared with the values of the original transition form factors. The results of form factors are used to estimate the total decay widths and branching ratios of these transitions. A comparison of our results on branching ratios with the predictions of other approaches is also presented.

We explore multicomponent dark matter models where the dark sector consists of multiple stable states with different mass scales, and dark forces coupling these states further enrich the dynamics. The multicomponent nature of the dark matter naturally arises in supersymmetric models, where both $R$ parity and an additional symmetry, such as a $Z_2$, is preserved. We focus on a particular model where the heavier component of dark matter carries lepton number and annihilates mostly to leptons. The heavier component, which is essentially a sterile neutrino, naturally explains the PAMELA and synchrotron signals, without an excess in antiprotons, which typically mars other models of weak scale dark matter. The lighter component, which may have a mass from a GeV to a TeV, may explain the DAMA signal, and may be visible in low threshold runs of CDMS and XENON, which search for light dark matter.

We study a pure gluon plasma in the context of quasiparticle models, where the plasma is considered as an ideal gas of massive bosons. In order to reproduce SU(3) gauge field lattice data within such a framework, we review briefly the necessity to use a temperature-dependent gluon mass which accounts for color interactions between the gluons near $T_{\mathrm{c}}$ and agrees with perturbative QCD at large temperatures. Consequently, we discuss the thermodynamics of systems with temperature-dependent Hamiltonians and clarify the situation about the possible solutions proposed in the literature to treat those systems consistently. We then focus our attention on two possible formulations which are thermodynamically consistent, and we extract the gluon mass from the equation of state obtained in SU(3) lattice QCD. We find that the thermal gluon mass is similar in both statistical formalisms. Finally, an interpretation of the gluon plasma as an ideal gas made of glueballs and gluons is also presented. The glueball mass is consistently computed within a relativistic formalism using a potential obtained from lattice QCD. We find that the gluon plasma might be a glueball-rich medium for $T\lesssim 1.13T_{\mathrm{c}}$ and suggest that glueballs could be detected in future experiments dedicated to quark-gluon plasma.

Assuming that the narrow state $X(3872)$ is a molecule state consisting of primarily $D^0{\overline{D}}^{*0}$, we calculate its mass within the constituent quark model. The attractive potential between $D^0$ and ${\overline{D}}^{*0}$ including one-$\sigma$ exchange and one-$\rho$ exchange is considered. We introduce the interaction between the heavy meson and light meson through the heavy meson form factor describing the heavy meson structure. The obtained mass of $X$ is consistent with the experimental value. Adopting this method, we study the various molecule states with hidden bottom quark.

Neutrinoless double beta decay ($\beta \beta 0\nu$) is among the only realistic probes of Majorana neutrinos. In the standard scenario, dominated by light neutrino exchange, the process amplitude is proportional to $m_{ee}$, the $e\mathrm{\text{−}}e$ element of the Majorana mass matrix. Naively, current data allow for vanishing $m_{ee}$, but this should be protected by an appropriate flavor symmetry. All such symmetries lead to mass matrices inconsistent with oscillation phenomenology. I perform a spurion analysis to break all possible Abelian symmetries that guarantee vanishing $\beta \beta 0\nu$ rates and search for minimally allowed values. I survey 230 broken structures to yield $m_{ee}$ values and current phenomenological constraints under a variety of scenarios. This analysis also extracts predictions for both neutrino oscillation parameters and kinematic quantities. Assuming reasonable tuning levels, I find that $m_{ee}>4\times {10}^{-6}\mathrm{eV}$ at 99% confidence. Bounds below this value might indicate the Dirac neutrino nature or the existence of new light (eV–MeV scale) degrees of freedom that can potentially be probed elsewhere.

Neutrinoless double beta decay $(\beta \beta 0\nu )$ is the only realistic probe of the Majorana nature of the neutrino. In the standard picture, its rate is proportional to $m_{ee}$, the $e\mathrm{\text{−}}e$ element of the Majorana neutrino mass matrix in the flavor basis. I explore minimally allowed $m_{ee}$ values within the framework of mass matrix anarchy where neutrino parameters are defined statistically at low energies. Distributions of mixing angles are well defined by the Haar integration measure, but masses are dependent on arbitrary weighting functions and boundary conditions. I survey the integration measure parameter space and find that for sufficiently convergent weightings, $m_{ee}$ is constrained between (0.01–0.4) eV at 90% confidence. Constraints from neutrino mixing data lower these bounds. Singular integration measures allow for arbitrarily small $m_{ee}$ values with the remaining elements ill-defined, but this condition constrains the flavor structure of the model’s ultraviolet completion. $\beta \beta 0\nu$ bounds below $m_{ee}\sim 5\times {10}^{-3}\mathrm{eV}$ should indicate symmetry in the lepton sector, new light degrees of freedom, or the Dirac nature of the neutrino.

There are several new features in the production, oscillations, and detection of the atmospheric neutrinos of low energies $E\lesssim 100\mathrm{MeV}$. The flavor ratio $r$ of muon to electron neutrino fluxes is substantially smaller than 2 and decreases with energy, a significant part of events is due to the decay of invisible muons at rest, etc. Oscillations in a two-layer medium (atmosphere-Earth) should be taken into account. We derive analytical and semianalytical expressions for the oscillation probabilities of these “sub-sub-GeV” neutrinos. The energy spectra of the $e$-like events in water Cherenkov detectors are computed, and the dependence of the spectra on the 2-3 mixing angle ${\theta }_{23}$, the 1-3 mixing, and the $CP$-violation phase are studied. We find that variations of ${\theta }_{23}$ in the presently allowed region change the number of $e$-like events by about 15%–20% as well as lead to distortion of the energy spectrum. The 1-3 mixing and $CP$ violation can lead to $\sim 10\%$ effects. Detailed study of the sub-sub-GeV neutrinos will be possible in future megaton-scale detectors.

Using data acquired with the CLEO-c detector at the CESR $e^{+}{e}^{-}$ collider, we measure branching fractions for $J/\psi$, $\psi (2S)$, and $\psi (3770)$ decays to $\gamma {\pi }^0$, $\gamma \eta$, and $\gamma {\eta }^{\prime }$. Defining $R_n\equiv \mathcal{B}[\psi (nS)\to \gamma \eta ]/\mathcal{B}[\psi (nS)\to \gamma {\eta }^{\prime }]$, we obtain $R_1=(21.1\pm 0.9)\%$ and, unexpectedly, an order of magnitude smaller limit, $R_2<1.8\%$ at 90% C.L. We also use $J/\psi \to \gamma {\eta }^{\prime }$ events to determine branching fractions of improved precision for the five most copious ${\eta }^{\prime }$ decay modes.

A general nonthreshold Bogomol’nyi-Prasad-Sommerfield $(F,D_p)$ [or $(D_{p-2},D_p)$] bound state can be described by a boundary state with a quantized world-volume electric (or magnetic) flux and is characterized by a pair of integers $(m,n)$. With this, we calculate explicitly the interaction amplitude between two such nonthreshold bound states with a separation $Y$ when each of the states is characterized by a pair of integers $(m_i,n_i)$ with $i=1,2$. With this result, one can show that the nondegenerate (i.e., $m_i{n}_i\ne 0$) interaction is, in general, attractive for the case of $(D_{p-2},D_p)$, but this is true and for certain only at large separation for the case of $(F,D_p)$. In either case, this interaction vanishes only if $m_1/n_1=m_2/n_2$ and $n_1{n}_2>0$. We also study the analytic structure of the corresponding amplitude and calculate, in particular, the rate of pair production of open strings in the case of $(F,D_p)$.

The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter $w$ varies from 0 to $-1$. In the case of tachyon field potential $V(\varphi )\to 0$ slower (faster) than $1/{\varphi }^2$ at infinity, dark energy (dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that $w$ is close to $-1$. We find that all the models exhibit unique behavior around the present epoch which is exactly the same as that of the thawing quintessence.

The stability of the topological kinks of the nonlinear ${\mathbb{S}}^2$-sigma model discovered by Alonso Izquierdo et al. is discussed by means of a direct estimation of the spectra of the second-order fluctuation operators around topological kinks. The one-loop mass shifts caused by quantum fluctuations around these kinks are computed using the Cahill-Comtet-Glauber formula. The (lack of) stability of the nontopological kinks is unveiled by application of the Morse index theorem. These kinks are identified as non-BPS states. There are two types of topological kinks coming from the twofold embedding of the sine-Gordon model in the massive nonlinear sigma model. It is shown that sine-Gordon kinks of only one type satisfy first-order equations and are accordingly BPS classical solutions. Finally, the interplay between instability and supersymmetry is explored.