In this work, we recalculate the charmless pure annihilation decays $B_s\to {\pi }^{+}{\pi }^{-}$ and $B^0\to K^{+}{K}^{-}$ by using the perturbative QCD (pQCD) factorization approach, and compare the pQCD predictions with currently available experimental measurements. By numerical calculations and phenomenological analysis, we found the following results: (a) one can provide a consistent pQCD interpretation for both the measured branching ratio $\mathrm{Br}(B_s^0\to {\pi }^{+}{\pi }^{-})$ and $\mathrm{Br}(B_d^0\to K^{+}{K}^{-})$ simultaneously; (b) the pQCD predictions for $\mathrm{Br}(B_s^0\to {\pi }^{+}{\pi }^{-})$ obtained by different authors are well consistent with each other; (c) our new pQCD prediction for $\mathrm{Br}(B_d^0\to K^{+}{K}^{-})$ agrees well with the measured values from CDF and LHCb Collaborations; and (d) the $CP$-violating asymmetry ${\mathcal{A}}_{CP}(B_d^0\to K^{+}{K}^{-})\approx 19\%$, which is large and may be detected at the LHCb and future Super-B factory experiments.

The recently reported would-be excess at 125 GeV in invariant mass distribution of $\gamma \gamma$ and of $l^{+}{l}^{+}{l}^{-}{l}^{-}$ obtained in the course of the Higgs boson search at LHC is tentatively interpreted as a scalar bound state of two $W$. Nonperturbative effects of electroweak interactions obtained by the application of the Bogoliubov compensation approach lead to such bound states due to the existence of anomalous three-boson gauge-invariant effective interactions. The application of this scheme gives satisfactory agreement with existing data without any adjusting parameter except for the bound state mass 125 GeV, while $\sigma \mathrm{BR}$ for $\gamma \gamma$ resonance is predicted to be twice as much as the value for the standard model Higgs. The decay channel $\gamma l^{+}{l}^{-}$ and an effect in $3\gamma$ production may serve as decisive checks of the interpretation.

A search for 5.5 MeV solar axions produced in the $p+d\to {}^3\mathrm{He}+\mathrm{A}$ (5.5 MeV) reaction was performed using the Borexino detector. The Compton conversion of axions to photons, $\mathrm{A}+e\to e+\gamma$; the axioelectric effect, $\mathrm{A}+e+Z\to e+Z$; the decay of axions into two photons, $\mathrm{A}\to 2\gamma$; and inverse Primakoff conversion on nuclei, $\mathrm{A}+Z\to \gamma +Z$, are considered. Model-independent limits on axion-electron ($g_{Ae}$), axion-photon ($g_{A\gamma }$), and isovector axion-nucleon ($g_{3AN}$) couplings are obtained: $|g_{Ae}\times g_{3AN}|\le 5.5\times {10}^{-13}$ and $|g_{A\gamma }\times g_{3AN}|\le 4.6\times {10}^{-11}{\mathrm{GeV}}^{-1}$ at $m_A<1\mathrm{MeV}$ (90% confidence level). These limits are 2–4 orders of magnitude stronger than those obtained in previous laboratory-based experiments using nuclear reactors and accelerators.

We present an improved determination of the total width of the top quark, ${\Gamma }_t$, using $5.4{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the D0 Collaboration at the Tevatron $p\overline{p}$ Collider. The total width ${\Gamma }_t$ is extracted from the partial decay width $\Gamma (t\to Wb)$ and the branching fraction $\mathcal{B}(t\to Wb)$. $\Gamma (t\to Wb)$ is obtained from the $t$-channel single top-quark production cross section and $\mathcal{B}(t\to Wb)$ is measured in $t\overline{t}$ events. For a top mass of 172.5 GeV, the resulting width is ${\Gamma }_t={2.00}_{-0.43}^{+0.47}\mathrm{GeV}$. This translates to a top-quark lifetime of ${\tau }_t=({3.29}_{-0.63}^{+0.90})\times {10}^{-25}\mathrm{s}$. We also extract an improved direct limit on the Cabibbo-Kobayashi-Maskawa quark-mixing matrix element $0.81<|V_{tb}|\le 1$ at 95% C.L. and a limit of $|V_{t{b}^{\prime }}|<0.59$ for a high-mass fourth-generation bottom quark assuming unitarity of the fourth-generation quark-mixing matrix.

A search for the $X(4140)$ state in $B^{+}\to J/\psi \varphi K^{+}$ decays is performed with $0.37{\mathrm{fb}}^{-1}$ of $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ collected by the LHCb experiment. No evidence for this state is found, in $2.4\sigma$ disagreement with a measurement by CDF. An upper limit on its production rate is set, $\mathcal{B}(B^{+}\to X(4140)K^{+})\times \mathcal{B}(X(4140)\to J/\psi \varphi )/\mathcal{B}(B^{+}\to J/\psi \varphi K^{+})<0.07$ at 90% confidence level.

We measure the branching fractions of $B^0\to J/\psi {\eta }^{(\prime )}$ decays with the complete Belle data sample of $772\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The results for the branching fractions are: $\mathcal{B}(B^0\to J/\psi \eta )=(12.3{\pm }_{1.7}^{1.8}\pm 0.7)\times {10}^{-6}$ and $\mathcal{B}(B^0\to J/\psi {\eta }^{\prime })<7.4\times {10}^{-6}$ at 90% confidence level. The $\eta \mathrm{\text{−}}{\eta }^{\prime }$ mixing angle is constrained to be less than 42.2° at 90% confidence level.

We reexamine the light deflection by an Ellis wormhole. The bending angle as a function of the ratio between the impact parameter and the throat radius of the wormhole is obtained in terms of a complete elliptic integral of the first kind. This result immediately yields asymptotic expressions in the weak field approximation. It is shown that an expression for the deflection angle derived (and used) in recent papers is valid at the leading order but it breaks down at the next order because of the nontrivial spacetime topology.

The recent measurements of the Cosmic Microwave Background anisotropies at arc minute angular scales performed by the ACT and SPT experiments are probing the damping regime of CMB fluctuations. The analysis of these data sets unexpectedly suggests that the effective number of relativistic degrees of freedom is larger than the standard value of $N_{\mathrm{eff}}=3.04$, and inconsistent with it at more than two standard deviations. In this paper we study the role of a mechanism that could affect the shape of the CMB angular fluctuations at those scales, namely, a change in the recombination process through variations in the fine structure constant. We show that the new CMB data significantly improve the previous constraints on variations of $\alpha$, with $\alpha /{\alpha }_0=0.984\pm 0.005$, i.e. hinting also at a more than two standard deviation from the current, local, value ${\alpha }_0$. A significant degeneracy is present between $\alpha$ and $N_{\mathrm{eff}}$, and when variations in the latter are allowed the constraints on $\alpha$ are relaxed and again consistent with the standard value. Deviations of either parameter from their standard values would imply the presence of new, currently unknown physics.

We show that coupling the standard model to a Lorentz symmetry-violating sector may coexist with viable phenomenology provided that the interaction between the two is mediated by higher-dimensional operators. In particular, if the new sector acquires anisotropic-scaling behavior above a “Hořava-Lifshitz” energy scale ${\Lambda }_{\mathrm{HL}}$ and couples to the standard model through interactions suppressed by $M_{\mathrm{pl}}$, the transmission of the Lorentz violation into the standard model is protected by the ratio ${\Lambda }_{\mathrm{HL}}^2/M_{\mathrm{pl}}^2$. A wide-scale separation ${\Lambda }_{\mathrm{HL}}\ll M_{\mathrm{pl}}$ can then make Lorentz-violating terms in the standard model sector within experimental bounds without fine-tuning. We first illustrate our point with a toy example of Lifshitz-type neutral fermion coupled to photon via the magnetic moment operator, and then implement similar proposal for the Hořava-Lifshitz gravity coupled to conventional Lorentz-symmetric matter fields. We find that most radiatively induced Lorentz violation can be controlled by a large-scale separation, but the existence of instantaneously propagating non-Lifshitz modes in gravity can cause a certain class of diagrams to remain quadratically divergent above ${\Lambda }_{\mathrm{HL}}$. Such problematic quadratic divergence however can be removed by extending the action with terms of higher Lifshitz-dimension, resulting in a completely consistent setup that can cope with the stringent tests of Lorentz invariance.

We investigate the evolution of a family of wormholes sustained by two matter components: one with homogeneous and isotropic properties $\rho (t)$ and another inhomogeneous and anisotropic ${\rho }_{\mathrm{in}}(t,r)$. The rate of expansion of these evolving wormholes is only determined by the isotropic and homogeneous matter component $\rho (t)$. Particularly, we consider a family of exact two-fluid evolving wormholes expanding with constant velocity and satisfying the dominant and the strong energy conditions in the whole space-time. In general, for the case of vanishing isotropic fluid $\rho (t)$ and cosmological constant $\Lambda$ the space expands with constant velocity, and for $\rho (t)=0$ and $\Lambda \ne 0$ the rate of expansion is determined by the cosmological constant. The considered here two-fluid evolving wormholes are a generalization of single fluid models discussed in previous works of the present authors [Phys. Rev. D 78, 104006 (2008); Phys. Rev. D 79, 024005 (2009)].

We construct quartic quasitopological gravity, a theory of gravity containing terms quartic in the curvature that yields second-order differential equations in the spherically symmetric case. Up to a term proportional to the quartic term in Lovelock gravity we find a unique solution for this quartic case, valid in any dimensionality larger than 4 except 8. This case is the highest degree of curvature coupling for which explicit black hole solutions can be constructed, and we obtain and analyze the various black hole solutions that emerge from the field equations in ($n+1$) dimensions. We discuss the thermodynamics of these black holes and compute their entropy as a function of the horizon radius. We then make some general remarks about $K$-th order quasitopological gravity, and point out that the basic structure of the solutions will be the same in any dimensionality for general $K$ apart from particular cases.

In the system of a gravitating $Q$ ball, there is a maximum charge $Q_{\max }$ inevitably, while in flat spacetime there is no upper bound on $Q$ in typical models such as the Affleck-Dine model. Theoretically, the charge $Q$ is a free parameter, and phenomenologically it could increase by charge accumulation. We address a question of what happens to $Q$ balls if $Q$ is close to $Q_{\max }$. First, without specifying a model, we show analytically that inflation cannot take place in the core of a $Q$ ball, contrary to the claim of previous work. Next, for the Affleck-Dine model, we analyze perturbation of equilibrium solutions with $Q\approx Q_{\max }$ by numerical analysis of dynamical field equations. We find that the extremal solution with $Q=Q_{\max }$ and unstable solutions around it are “critical solutions,” which means the threshold of black-hole formation.

Classical electrodynamics in flat $3+1$ space-time has a very special retarded propagator $\sim \delta (x^2)$ localized on the light cone, so that a particle does not interact with its past field. However, this is an exception, and in flat odd-dimensional space-times as well as generic curved spaces, this is not so. In this work, we show that the so-called self-force is not only nonzero, but it matches (in $2+1$ dimensions) the radiation reaction force derived from the radiation intensity.

We argue that classical bulk gravitational radiation effects in AdS/CFT, previously ignored because of their subleading nature in the $1/N_c$ expansion, are magnified by powers of large Lorentz factors $\gamma$ for ultrarelativistic jets, thereby dominating other forms of jet energy loss in holography at finite temperature. We make use of the induced gravitational self-force in thermal anti-de Sitter to estimate its effects. In a thermal medium, relativistic jets may lose most of their energy through longitudinal drag caused by the energy accumulated in their nearby field as they zip through the strongly coupled plasma.

Lightlike Galileon solutions have been used to investigate the chronology problem in Galileon-like theories, and in some cases may also be considered as solitons, evading a nonexistence constraint from a zero-mode argument. Their stabilities have been analyzed via “local” approximation, which appears to suggest that all these lightlike solutions are stable. We reanalyze the stability problem by solving the linear perturbation equation exactly, and point out that the finite energy condition is essential for the lightlike solitons to be stable. We also clarify potential ghost instabilities and why the zero-mode argument cannot be naively generalized to include the lightlike solitons.

A large family of new black hole solutions in $2+1$-dimensional Einstein-power-Maxwell gravity with prescribed physical properties is derived. We show with particular examples that according to the power parameter $k$ of the Maxwell field, the obtained solutions may be asymptotically flat for $1/2<k<1$ or nonflat for $k>1$ in the vanishing cosmological constant limit. We study the thermodynamic properties of the solution with two different models, and it is shown that thermodynamic quantities satisfy the first law. The behavior of the heat capacity indicates that by employing the $1+1$-dimensional dilaton analogy the local thermodynamic stability is satisfied.

We study the general parity-preserving model of 3-dimensional gravity with propagating torsion, with a focus on its nonlinear dynamics in the AdS sector. The model is shown to posses the black hole with torsion as a vacuum solution, provided we adopt certain restrictions on its coupling constants. The canonical analysis in the AdS asymptotic region yields the conserved charges of the black hole and the central charges of the asymptotic conformal symmetry.

We investigate the dynamics of single and multiple scalar fields with exponential potentials, leading to power-law and assisted inflation, in loop quantum cosmology. Unlike in the classical theory, dynamical trajectories in loop quantum cosmology are generically nonsingular, with a big bounce replacing classical big bang in the Planck regime. Post-bounce, after a phase of superinflation, dynamical trajectories evolve towards the classical attractor in the inflationary scenarios. Depending on the initial conditions, bounce is shown to occur in kinetic as well as potential dominated regimes. We analyze the number of e-foldings resulting from the phase of superinflation and find the dependence of the maximum possible number of e-foldings on the equation of state at the bounce and on the steepness of the potential. We find that if the potential is not steep, this phase can lead to a large number of e-foldings in power-law inflation. For the assisted inflation scenario, an increase in the number of fields can yield a significant increase in the number of e-foldings during superinflation.

The renormalized energy-momentum tensor of vacuum was deeply explored many years ago. The main result of these studies was that such a tensor should satisfy the conservation laws which reflect the covariance of the theory in the presence of loop corrections. In view of this general result, we address two important questions, namely, how to implement the momentum cutoff in a covariant way and whether this general result holds in the theory with spontaneous symmetry breaking. In the last case, some new interesting details arise, and although the calculations are more involved, we show that the final result satisfies the conservation laws.

A number of well-motivated extensions of the $\Lambda \mathrm{CDM}$ concordance cosmological model postulate the existence of a population of sources embedded in the cosmic microwave background. One such example is the signature of cosmic bubble collisions which arise in models of eternal inflation. The most unambiguous way to test these scenarios is to evaluate the full posterior probability distribution of the global parameters defining the theory; however, a direct evaluation is computationally impractical on large datasets, such as those obtained by the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck. A method to approximate the full posterior has been developed recently, which requires as an input a set of candidate sources which are most likely to give the largest contribution to the likelihood. In this article, we present an improved algorithm for detecting candidate sources using optimal filters, and apply it to detect candidate bubble collision signatures in WMAP 7-year observations. We show both theoretically and through simulations that this algorithm provides an enhancement in sensitivity over previous methods by a factor of approximately two. Moreover, no other filter-based approach can provide a superior enhancement of these signatures. Applying our algorithm to WMAP 7-year observations, we detect eight new candidate bubble collision signatures for follow-up analysis.