We use a novel method to calculate analytically the QCD instanton prefactor due to a quark field carrying a small-mass parameter $m$. In the SU(2) instanton background of size $\rho$, the spinor effective action ${\Gamma }^F$ (in the minimal subtraction scheme), which gives rise to the prefactor $\exp (-{\Gamma }^F)$, is shown to have the small-$m\rho$ behavior ${\Gamma }^F=-\ln (m/\mu )-\ln (\mu \rho )/3$ $-2\alpha (1/2)-(m\rho {)}^2$ $\{\ln (m\rho /2)+\gamma +1/2\}$ $-2(m\rho {)}^4\{-{ln}^2(m\rho )/4$ $+\ln (m\rho )(1/2-\gamma +\ln 2)/2$ $+C\}+O((m\rho {)}^6)$, where $\gamma =0.577216\dots$, $\alpha (1/2)=0.145873\dots$, and our numerically evaluated value for the constant $C$ is $C=-0.382727\dots$. A good agreement between this form and the numerically exact calculation is found if $(m\rho )\lesssim 0.8$.

A Lifshitz point is described by a quantum field theory with anisotropic scale invariance (but not Galilean invariance). In [8], gravity duals were conjectured for such theories. We construct analytically a black hole that asymptotes to a vacuum Lifshitz solution; this black hole solves the equations of motion of some simple (but somewhat strange) extensions of the models of [8]. We study its thermodynamics and scalar response functions. The scalar wave equation turns out to be exactly solvable. Interestingly, the Green’s functions do not exhibit the ultralocal behavior seen previously in the free Lifshitz scalar theory.

We investigate the Tolman-Oppenheimer-Volkoff equations for the generalized Chaplygin gas with the aim of extending the findings of V. Gorini, U. Moschella, A. Y. Kamenshchik, V. Pasquier, and A. A. Starobinsky [Phys. Rev. D 78, 064064 (2008)]. We study both the standard case, where we reproduce some previous results, and the phantom case. In the phantom case we show that even a superluminal group velocity arising for $\alpha >1$ cannot prevent the divergence of the pressure at a finite radial distance. Finally, we investigate how a modification of the generalized Chaplygin gas equation of state, required by causality arguments at densities very close to $\Lambda$, affects the results found so far.

We investigate the geodetic precession effect of a parallelly transported spin vector along a circular geodesic in five-dimensional squashed Kaluza-Klein black hole spacetime. Then we derive the higher-dimensional correction of the precession angle to general relativity. We find that the correction is proportional to the square of (size of extra dimension)/(gravitational radius of central object).

A Weyl solution describing two Schwarzschild black holes is considered. We focus on the ${\mathbb{Z}}_2$ invariant solution, with Arnowitt-Deser-Misner mass $M_{\mathrm{ADM}}=2M_{\mathrm{K}}$, where $M_{\mathrm{K}}$ is the Komar mass of each black hole. For this solution the set of fixed points of the discrete symmetry is a totally geodesic submanifold. The existence and radii of circular photon orbits in this submanifold are studied, as functions of the distance $2L$ between the two black holes. For $L\to 0$ there are two such orbits, corresponding to $r=3M_{\mathrm{ADM}}$ and $r=2M_{\mathrm{ADM}}$ in Schwarzschild coordinates. As the distance increases, it is shown that the two photon orbits approach one another and merge when $M_{\mathrm{K}}=\phi L$, where $\phi$ is the golden ratio. Beyond this distance there exist no circular photon orbits. The two null orbits delimit a forbidden band for timelike circular orbits, which is interpreted in terms of optical geometry. For large $L$, timelike circular orbits are allowed everywhere, as in the analogous Newtonian problem. The analysis is generalized by considering a ${\mathbb{Z}}_2$ invariant Weyl solution with an array of $N$ black holes and also by charging the black holes, which connects the Weyl solution to a Majumdar-Papapetrou spacetime.

A unified treatment of mass varying dark matter coupled to cosmonlike dark energy is shown to result in effective generalized Chaplygin gas (GCG) scenarios. The mass varying mechanism is treated as a cosmon field inherent effect. Coupling dark matter with dark energy allows for reproducing the conditions for the present cosmic acceleration and for recovering the stability resulting from a positive squared speed of sound $c_s^2$, as in the GCG scenario. The scalar field mediates the nontrivial coupling between the dark matter sector and the sector responsible for the accelerated expansion of the Universe. The equation of state of perturbations is the same as that of the background cosmology so that all the effective results from the GCG paradigm are maintained. Our results suggest the mass varying mechanism, when obtained from an exactly soluble field theory, as the one responsible for the stability issue and for the cosmic acceleration of the Universe.

Phantom cosmology provides a unique opportunity to “connect” the phantom-driven (low energy meV scale) dark energy phase to the (high energy grand unified theory scale) inflationary era. This is possible because the energy density increases in phantom cosmology. We present a concrete model where the energy density, but not the scale factor, cycles through phases of standard radiation/matter domination followed by dark energy/inflationary phases, and the pattern repeating itself. An interesting feature of the model is that once we include interactions between the “phantom fluid” and ordinary matter, the big-rip singularity is avoided with the phantom phase naturally giving way to a near exponential inflationary expansion.

The tree-level semileptonic ${\Lambda }_b\to pl\nu$ and ${\Lambda }_c\to nl\nu$ transitions are investigated using the light cone QCD sum rules approach in full theory. The spin $1/2$, ${\Lambda }_Q$ baryon with $Q=b$ or $c$, is considered by the most general form of its interpolating current. The time ordering product of the initial and transition currents is expanded in terms of the nucleon distribution amplitudes with different twists. Considering two sets of independent input parameters entering to the nucleon wave functions, namely, QCD sum rules and lattice QCD parameters, the related form factors and their heavy quark effective theory limits are calculated and compared with the existing predictions of other approaches. It is shown that our results satisfy the heavy quark symmetry relations for lattice input parameters and $b$ case exactly and the maximum violation is for charm case and QCD sum rules input parameters. The obtained form factors are used to compute the transition rates both in full theory and heavy quark effective theory. A comparison of the results on decay rate of ${\Lambda }_b\to pl\nu$ with those predicted by other phenomenological methods or the same method in heavy quark effective theory with different interpolating current and distribution amplitudes of the ${\Lambda }_b$ is also presented.

A first study of critical behavior in the vicinity of the chiral phase transition of ($2+1$)-flavor QCD is presented. We analyze the quark mass and volume dependence of the chiral condensate and chiral susceptibilities in QCD with two degenerate light quark masses and a strange quark. The strange quark mass ($m_s$) is chosen close to its physical value; the two degenerate light quark masses ($m_l$) are varied in a wide range $1/80\le m_l/m_s\le 2/5$, where the smallest light quark mass value corresponds to a pseudoscalar Goldstone mass of about 75 MeV. All calculations are performed with staggered fermions on lattices with temporal extent $N_{\tau }=4$. We show that numerical results are consistent with $O(N)$ scaling in the chiral limit. We find that in the region of physical light quark mass values, $m_l/m_s\simeq 1/20$, the temperature and quark mass dependence of the chiral condensate is already dominated by universal properties of QCD that are encoded in the scaling function for the chiral order parameter, the magnetic equation of state. We also provide evidence for the influence of thermal fluctuations of Goldstone modes on the chiral condensate at finite temperature. At temperatures below, but close to the chiral phase transition at vanishing quark mass, this leads to a characteristic dependence of the light quark chiral condensate on the square root of the light quark mass.

The decays of ${\chi }_{cJ}\to {\pi }^{+}{\pi }^{-}$, $K^{+}{K}^{-}$ ($J=0,2$) are discussed within the standard and modified hard-scattering approach when including the contributions from twist-3 distribution amplitudes and wave functions of the light pseudoscalar meson. A model for twist-2 and twist-3 distribution amplitudes and wave functions of the pion and kaon with BHL prescription are proposed as the solution to the end-point singularities. The results show that the contributions from twist-3 parts are actually not power suppressed comparing with the leading-twist contribution. After including the effects from the transverse momentum of light meson valence-quark state and Sudakov factors, the decay widths of the ${\chi }_{cJ}$ into pions or kaons are comparable with the their experimental data.

The use of energy flow is investigated as a diagnostic tool for determining the color SU(3) representation of new resonances. It is found that the pattern of soft gluon radiation into a rapidity gap depends on color flow in the hard scattering, and reflects the gauge content of new physics. The massive soft anomalous dimension matrix for rapidity gap events is introduced for describing soft gluon emission analytically in heavy quark pair production. A gap fraction is used for quantifying the amount of soft radiation into the gap region. In general, the results illustrate that radiation is greater for a singlet resonance than for an octet. Especially, it is found that the quantitative difference is quite distinguishable for spin-1 resonances, depending on the gauge content in the new sector.

We study scalar glueballs and scalar mesons at $T\ne 0$ in the soft wall holographic QCD model. We find that, using the anti-de Sitter–black-hole metric for all values of the temperature, the masses of the hadronic states decrease and the widths become broader when $T$ increases, and there are temperatures for which the states disappear from the scalar glueball and scalar meson spectral functions. However, the values of the temperatures in correspondence of which such phenomena occur are low, of the order of 40–60 MeV. A consistent holographic description of in-medium effects on hadron properties should include the Hawking-Page transition, which separates the phase with the anti-de Sitter metric at small temperatures from the phase with anti-de Sitter–black-hole metric at high temperatures.

This article gives the perturbative next-to-next-to-leading order results for the moments of the most commonly used event shape variables associated to three-jet events in electron-positron annihilation: thrust, heavy jet mass, wide jet broadening, total jet broadening, $C$ parameter and the Durham three-to-two-jet transition variable.

We study how fluxes on the domain wall world volume modify quantum fusion of two distant parallel domain walls into a composite wall. The elementary wall fluxes can be separated into parallel and antiparallel components. The parallel component affects neither the binding energy nor the process of quantum merger. The antiparallel fluxes, instead, increase the binding energy and, against naive expectations, suppress quantum fusion. In the small-flux limit we explicitly find the bounce solution and the fusion rate as a function of the flux. We argue that at large (antiparallel) fluxes there exists a critical value of the flux (versus the difference in the wall tensions), which switches off quantum fusion altogether. This phenomenon of flux-related wall stabilization is rather peculiar: it is unrelated to any conserved quantity. Our consideration of the flux-related wall stabilization is based on substantiated arguments that fall short of complete proof.

The behavior of a massive scalar particle on the spacetime surrounding a monopole is studied from a quantum mechanical point of view. All the boundary conditions necessary to turn the spatial portion of the wave operator self-adjoint are found and their importance to the quantum interpretation of singularities is emphasized.

We present long term evolutions of a single black hole of mass $M$ with the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) system using pseudospectral methods. For our simulations we use the SGRID code where the BSSN system is implemented in its standard second order in space form. Previously we found that such simulations are quite unstable. The main goal of this paper is to present two improvements which now allow us to evolve for longer times. The first improvement is related to the boundary conditions at the excised black hole interior. We now use a gauge condition that ensures that all modes are going into the black hole, so that no boundary conditions are needed at the excision surface. The second more significant improvement has to do with our particular numerical method and involves filters based on projecting the double Fourier expansions used for the angular dependence onto spherical harmonics. With these two improvements it is now easily possible to evolve for several thousand $M$. The only remaining limitation seems to be the radiative outer boundary conditions used here. Yet this problem can be ameliorated by pushing out the location of the outer boundary, which leads to even longer run times.

Nongaussianity in the microwave background radiation is bound to play a key role in giving us clues about the physics of the very early Universe. However, the associated calculations, at second and even third order in perturbation theory, tend to be complicated to the point of obscuring simple underlying physical processes. In this note, we present a simple analytic procedure for approximating the nonlinearity parameters $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ for cyclic models in which the cosmological perturbations are generated via the entropic mechanism. Our approach is quick, physically transparent, and agrees well with the results of numerical calculations.

We discuss the sensitivity of neutrino experiments at the luminosity frontier to generic hidden sectors containing new (sub)-GeV neutral states. The weak interaction of these states with the standard model can be efficiently probed through all of the allowed renormalizable “portals” (in the Higgs, vector, and neutrino sectors) at fixed target proton beam facilities, with complementary sensitivity to colliders. We concentrate on the kinetic-mixing vector portal, and show that certain regions of the parameter space for a new $\mathrm{U}(1{)}_S$ gauge sector with long-lived sub-GeV mass states decaying to standard model leptons are already severely constrained by the data sets at LSND, MiniBooNE, and NuMI/MINOS. Furthermore, scenarios in which portals allow access to stable neutral particles, such as MeV-scale dark matter, generally predict that the neutrino beam is accompanied by a “dark matter beam,” observable through neutral-current-like interactions in the detector. As a consequence, we show that the LSND electron recoil event sample currently provides the most stringent direct constraint on MeV-scale dark matter models.

Spherically symmetric thin-shell wormholes are studied within the framework of Einstein-Born-Infeld theory. We analyze the exotic matter content, and find that for certain values of the Born-Infeld parameter the amount of exotic matter on the shell can be reduced in relation with the Maxwell case. We also examine the mechanical stability of the wormhole configurations under radial perturbations preserving the spherical symmetry.