We discuss the interplay between higher orders of the perturbative QCD expansion and higher-twist contributions in the analysis of recent Jefferson Lab data on the lowest moments of spin-dependent proton and neutron structure functions ${\Gamma }_1^{p,n}(Q^2)$ and Bjorken sum rule function ${\Gamma }_1^{p-n}(Q^2)$ at $0.05<Q^2<3{\mathrm{GeV}}^2$. We demonstrate that the values of the higher-twist coefficients ${\mu }_{2k}^{p,n}$ extracted from the mentioned data by using the singularity-free analytic perturbation theory provide a better convergence of the higher-twist series than with the standard perturbative QCD. From the high-precision proton data, we extract the value of the singlet axial charge $a_0(1{\mathrm{GeV}}^2)=0.33\pm 0.05$. We observe a slow $Q^2$ dependence of fitted values of the twist coefficient ${\mu }_4$ and $a_0$ when going to lower energy scales, which can be explained by the well-known renormalization group evolution of ${\mu }_4(Q^2)$ and $a_0(Q^2)$. As the main result, a good quantitative description of all the Jefferson Lab data sets down to $Q\simeq 350\mathrm{MeV}$ is achieved.

We consider the top-quark pair production at the upcoming LHC and investigate the contributions of the new particles to the related observables within the framework of the littlest Higgs model with $T$-parity(LHT). It is found that the LHT model can generate significant corrections to the $t\overline{t}$ production cross section and their spin correlations.

We calculate the neutral kaon mixing parameter $B_K$ in unquenched lattice QCD using asqtad-improved staggered sea quarks and domain-wall valence quarks. We use the “$2+1$” flavor gauge configurations generated by the MILC Collaboration, and simulate with multiple valence and sea-quark masses at two lattice spacings of $a\approx 0.12\mathrm{fm}$ and $a\approx 0.09\mathrm{fm}$. We match the lattice determination of $B_K$ to the continuum value using the nonperturbative method of Rome-Southampton, and extrapolate $B_K$ to the continuum and physical quark masses using mixed-action chiral perturbation theory. The “mixed-action” method enables us to control all sources of systematic uncertainty and therefore to precisely determine $B_K$; we find a value of $B_K^{\overline{\mathrm{MS}},\mathrm{NDR}}(2\mathrm{GeV})=0.527(6)(21)$, where the first error is statistical and the second is systematic.

Recent work on QCD-like theories has shown that the addition of adjoint fermions obeying periodic boundary conditions to gauge theories on $R^3\times S^1$ can lead to a restoration of center symmetry and confinement for sufficiently small circumference $L$ of $S^1$. At small $L$, perturbation theory may be used reliably to compute the effective potential for the Polyakov loop $P$ in the compact direction. Periodic adjoint fermions act in opposition to the gauge fields, which by themselves would lead to a deconfined phase at small $L$. In order for the fermionic effects to dominate gauge field effects in the effective potential, the fermion mass must be sufficiently small. This indicates that chiral symmetry breaking effects are potentially important. We develop a Polyakov–Nambu–Jona-Lasinio (PNJL) model which combines the known perturbative behavior of adjoint QCD models at small $L$ with chiral symmetry breaking effects to produce an effective potential for the Polyakov loop $P$ and the chiral order parameter $\overline{\psi }\psi$. A rich phase structure emerges from the effective potential. Our results are consistent with the recent lattice simulations of Cossu and D’Elia, which found no evidence for a direct connection between the small-$L$ and large-$L$ confining regions. Nevertheless, the two confined regions are connected indirectly if an extended field theory model with an irrelevant four-fermion interaction is considered. Thus the small-$L$ and large-$L$ regions are part of a single confined phase.

The mixings between Berenstein-Maldacena-Nastase (BMN) operators with two scalar impurities and those with a scalar fermion pair are discussed to the lowest order at planar level. For this purpose, matrix model effective vertices are calculated to $O(g^3)$. All the mixing patterns are explicitly obtained.

I review the problem of motion for small bodies in general relativity, with an emphasis on developing a self-consistent treatment of the gravitational self-force. An analysis of the various derivations extant in the literature leads me to formulate an asymptotic expansion in which the metric is expanded while a representative worldline is held fixed. I discuss the utility of this expansion for both exact point particles and asymptotically small bodies, contrasting it with a regular expansion in which both the metric and the worldline are expanded. Based on these preliminary analyses, I present a general method of deriving self-consistent equations of motion for arbitrarily structured (sufficiently compact) small bodies. My method utilizes two expansions: an inner expansion that keeps the size of the body fixed, and an outer expansion that lets the body shrink while holding its worldline fixed. By imposing the Lorenz gauge, I express the global solution to the Einstein equation in the outer expansion in terms of an integral over a worldtube of small radius surrounding the body. Appropriate boundary data on the tube are determined from a local-in-space expansion in a buffer region where both the inner and outer expansions are valid. This buffer-region expansion also results in an expression for the self-force in terms of irreducible pieces of the metric perturbation on the worldline. Based on the global solution, these pieces of the perturbation can be written in terms of a tail integral over the body’s past history. This approach can be applied at any order to obtain a self-consistent approximation that is valid on long time scales, both near and far from the small body. I conclude by discussing possible extensions of my method and comparing it to alternative approaches.

The 3.5 post-Newtonian (PN) order is tackled by extending the canonical formalism of Arnowitt, Deser, and Misner to spinning objects. This extension is constructed order by order in the PN setting by utilizing the global Poincaré invariance as the important consistency condition. The formalism is valid to linear order in the single spin variables. Agreement with a recent action approach is found. A general formula for the interaction Hamiltonian between matter and transverse-traceless part of the metric at 3.5PN is derived. The wave equation resulting from this Hamiltonian is considered in the case of the constructed formalism for spinning objects. Agreement with the Einstein equations is found in this case. The energy flux at the spin-orbit level is computed.

We show the existence of a rather general class of closed cosmological models of Bianchi type IX that do not exhibit recollapse but expand for all times. This is despite the fact that these models satisfy the strong energy condition by a wide margin.

We consider an extension of the holographic Ricci dark energy model by introducing an interaction between dark energy and matter. In this model, the dark energy density is given by ${\rho }_{\Lambda }=-\frac{1}{2}\alpha M_p^2\mathcal{R}$, where $\mathcal{R}$ is the Ricci scalar curvature, $M_p$ is the reduced Planck mass, and $\alpha$ is a dimensionless parameter. The interaction rate is given by $Q=\gamma H{\rho }_{\Lambda }$, where $H$ is the Hubble expansion rate, and $\gamma$ is a dimensionless parameter. We investigate current observational constraints on this model by applying the type Ia supernovae, the baryon acoustic oscillation and the cosmic microwave background anisotropy data. It is shown that a nonvanishing interaction rate is favored by the observations. The best fit values are $\alpha =0.45\pm 0.03$ and $\gamma =0.15\pm 0.03$ for the present dark energy density parameter ${\Omega }_{\Lambda 0}=0.73\pm 0.03$.

We discuss general on-shell couplings of a scalar with two $Z$ bosons using an operator analysis. In addition to the operator that originated from the Higgs mechanism, two dimension-five operators, one $CP$ even and one $CP$ odd, are generated only at the loop level. Simple formulas are derived for the differential decay distributions when the $Z$ pair subsequently decays into four leptons by computing the helicity amplitudes, from which it is shown the $CP$-odd operator merely induces a phase shift in the azimuthal angular distribution between the two decay planes of the $Z$ bosons. We also investigate new physics scenarios giving rise to loop-induced decays of a scalar into the $ZZ$ pair, and argue that the total decay width of such a scalar would be an order-of-magnitude smaller than that of a Higgs boson, should such decays be observed in the early running of the LHC. Therefore, the total decay width alone is a strong indicator of the Higgs nature, or the lack thereof, of a scalar resonance in $ZZ$ final states. In addition, we study the possibility of using the azimuthal angular distribution to disentangle effects among all three operators.

The hadronic decays of ${\chi }_{c1}\to VV$ and ${\chi }_{c2}\to VP$ are supposed to be suppressed by the helicity selection rule in the perturbative QCD framework. With an effective Lagrangian method, we show that the intermediate charmed meson loops can provide a mechanism for the evasion of the helicity selection rule, and result in sizeable decay branching ratios in some of those channels. The theoretical predictions can be examined by the forthcoming BES-III data in the near future.

The top quark forward-backward asymmetry $A_{\mathrm{FB}}^t$ measured at the Tevatron is above the standard model prediction by more than $2\sigma$ deviation, which might be a harbinger for new physics. In this work we examine the contribution to $A_{\mathrm{FB}}^t$ in two different new physics models: one is the minimal supersymmetric model without $R$ parity which contributes to $A_{\mathrm{FB}}^t$ via sparticle-mediated $t$ channel process $d\overline{d}\to t\overline{t}$; the other is the third-generation enhanced left-right model which contributes to $A_{\mathrm{FB}}^t$ via $Z^{\prime }$-mediated $t$ channel or $s$ channel processes. We find that in the parameter space allowed by the $t\overline{t}$ production rate and the $t\overline{t}$ invariant mass distribution at the Tevatron, the left-right model can enhance $A_{\mathrm{FB}}^t$ to within the $2\sigma$ region of the Tevatron data for the major part of the parameter space, and in optimal case $A_{\mathrm{FB}}^t$ can reach 12% which is slightly below the $1\sigma$ lower bound. For the minimal supersymmetric model without $R$ parity, only in a narrow part of the parameter space can the ${\lambda }^{\prime \prime }$ couplings enhance $A_{\mathrm{FB}}^t$ to within the $2\sigma$ region while the ${\lambda }^{\prime }$ couplings just produce negative contributions to worsen the fit.

We present gravitational aspects of braneworld models endowed with torsion terms both in the bulk and on the brane. In order to investigate a conceivable and measurable gravitational effect, arising genuinely from bulk torsion terms, we analyze the variation in the black hole area by the presence of torsion. Furthermore, we extend the well-known results about consistency conditions in a framework that incorporates brane torsion terms. It is shown, in a rough estimate, that the resulting effects are generally suppressed by the internal space volume. This formalism provides manageable models and their possible ramifications into some aspects of gravity in this context, and cognizable corrections and physical effects as well.

We analyze momentarily static initial data sets of the gravitational field produced by two-point sources in five-dimensional Kaluza-Klein spacetimes. These initial data sets are characterized by the mass, the separation of sources and the size of an extra dimension. Using these initial data sets, we discuss the condition for black hole formation, and propose a new conjecture which is a hybrid of the four-dimensional hoop conjecture and the five-dimensional hyperhoop conjecture. By using the new conjecture, we estimate the cross section of black hole formation due to collisions of particles in Kaluza-Klein spacetimes. We show that the mass dependence of the cross section gives us information about the size and the number of the compactified extra dimensions.

Tidal torques from a binary black hole empty out the central regions in any circumbinary gaseous accretion disk. The balance between tidal torques and viscosity maintain the inner edge of the disk at a radius $r\sim 1.5a–2a$, where $a$ is the binary semimajor axis. Eventually, the inspiraling binary decouples from the disk and merges, leaving behind a central hollow (“donut hole”) in the disk orbiting the remnant black hole. We present a simple, time-dependent, Newtonian calculation that follows the secular (viscous) evolution of the disk as it fills up the hollow down to the black hole innermost stable circular orbit and then relaxes to stationary equilibrium. We use our model to calculate the electromagnetic radiation (“afterglow”) spectrum emitted during this transient accretion epoch. Observing the temporal increase in the total electromagnetic flux and the hardening of the spectrum as the donut hole fills may help confirm a binary black hole merger detected by a gravitational wave interferometer. We show how the very existence of the initial hollow can lead to super-Eddington accretion during this secular phase if the rate is not very far below Eddington prior to decoupling. Our model, though highly idealized, may be useful in establishing some of the key parameters, thermal emission features and scalings that characterize this transient. It can serve as a guide in the design and calibration of future radiation-magnetohydrodynamic simulations in general relativity.

We present a class of new black hole solutions in $D$-dimensional Lovelock gravity theory. The solutions have a form of direct product ${\mathcal{M}}^m\times {\mathcal{H}}^n$, where $D=m+n$, ${\mathcal{H}}^n$ is a negative constant curvature space, and the solutions are characterized by two integration constants. When $m=3$ and 4, these solutions reduce to the exact black hole solutions recently found by Maeda and Dadhich in Gauss-Bonnet gravity theory. We study thermodynamics of these black hole solutions. Although these black holes have a nonvanishing Hawking temperature, surprisingly, the mass of these solutions always vanishes. While the entropy also vanishes when $m$ is odd, it is a constant determined by an Euler characteristic of ($m-2$)-dimensional cross section of black hole horizon when $m$ is even. We argue that the constant in the entropy should be thrown away. Namely, when $m$ is even, the entropy of these black holes also should vanish. We discuss the implications of these results.

We discuss various ways in which the computation of conservative gravitational self-force (GSF) effects on a point mass moving in a Schwarzschild background can inform us about the basic building blocks of the effective one-body (EOB) Hamiltonian. We display the information which can be extracted from the recently published GSF calculation of the first-GSF-order shift of the orbital frequency of the last stable circular orbit, and we combine this information with the one recently obtained by comparing the EOB formalism to high-accuracy numerical relativity data on coalescing binary black holes. The information coming from GSF data helps to break the degeneracy (among some EOB parameters) which was left after using comparable-mass numerical relativity data to constrain the EOB formalism. We suggest various ways of obtaining more information from GSF computations: either by studying eccentric orbits, or by focusing on a special zero-binding zoom-whirl orbit. We show that logarithmic terms start entering the post-Newtonian expansions of various (EOB and GSF) functions at the fourth post-Newtonian level, and we analytically compute the first logarithm entering a certain, gauge-invariant “redshift” GSF function (defined along the sequence of circular orbits).

We develop a variant of the generalized slow roll approach for calculating the curvature power spectrum that is well suited for order unity deviations in power caused by sharp features in the inflaton potential. As an example, we show that predictions for a step function potential, which has been proposed to explain order unity glitches in the cosmic microwave background temperature power spectrum at multipoles $\ell =20–40$, are accurate at the percent level. Our analysis shows that to good approximation there is a single source function that is responsible for observable features and that this function is simply related to the local slope and curvature of the inflaton potential. These properties should make the generalized slow roll approximation useful for inflation-model-independent studies of features, both large and small, in the observable power spectra.

We calculate the frequency dependence of the gravitational wave background arising at second order of cosmological perturbation theory due to mixing of tensor and scalar modes. The calculation of the induced gravitational background is performed for two special cases: for the power spectrum of scalar perturbations which has a peak at some scale and for the scalar spectrum predicted by the inflationary model with the running mass potential. We show that the amplitudes of the induced gravitational background, in the frequency region $\sim {10}^{-3}–{10}^3\mathrm{Hz}$, are effectively constrained by results of studies of primordial black hole production in the early universe. We argue that though today’s LIGO bound on ${\mathcal{P}}_{\mathcal{R}}(k)$ is weaker than the primordial black hole one, Advanced LIGO will be able to set a stronger bound, and in the future the ground-based interferometers of the LIGO type will be suitable for obtaining constraints on primordial black holes number density in the mass range $\sim {10}^{11}–{10}^{15}\mathrm{g}$.

In this paper we develop a Markov chain Monte Carlo code to study the dark matter properties in frameworks to interpret the recent observations of cosmic ray electron/positron excesses. We assume that the dark matter particles couple dominantly to leptons and consider two cases, annihilating or decaying into lepton pairs, respectively. The constraint on the central density profile from the H.E.S.S. observation of diffuse $\gamma$ rays around the Galactic center is also included in the Markov chain Monte Carlo code self-consistently. In the numerical study, we have considered two cases of the background: fixed $e^{+}{e}^{-}$ background and the relaxed one. Two data sets of electrons/positrons, i.e. $\mathrm{PAMELA}+\mathrm{ATIC}$ (Data set I) and $\mathrm{PAMELA}+\mathrm{Fermi}\mathrm{\text{−}}\mathrm{LAT}+\mathrm{H}.\mathrm{E}.\mathrm{S}.\mathrm{S}.$ (Data set II), are fitted independently, considering the current inconsistence between the observational data. We find that for Data set I, dark matter with $m_{\chi }\approx 0.70\mathrm{TeV}$ for annihilation (or 1.4 TeV for decay) and a non-negligible branching ratio to $e^{+}{e}^{-}$ channel is favored; while for Data set II, $m_{\chi }\approx 2.2\mathrm{TeV}$ for annihilation (or 4.5 TeV for decay) and the combination of ${\mu }^{+}{\mu }^{-}$ and ${\tau }^{+}{\tau }^{-}$ final states can best fit the data. We also show that the background of electrons and positrons actually will significantly affect the branching ratios. The H.E.S.S. observation of $\gamma$ rays in the Galactic center ridge puts a strong constraint on the central density profile of the dark matter halo for the annihilation dark matter scenario. In this case the Navarro-Frenk-White profile, which is regarded as the typical predication from the cold dark matter scenario, is excluded with a high significance ($>3\sigma$). For the decaying dark matter scenario, the constraint is much weaker.