Finite temperature modifies the running of the QCD coupling ${\alpha }_s(k,T)$ with resolution $k$. After calculating the thermal quark and gluon masses self-consistently, we determine the quark-quark and quark-gluon cross sections in the plasma based on the running coupling. We find that the running coupling enhances these cross sections by factors of two to four depending on the temperature. We also compute the energy loss $\frac{dE}{dx}$ of a high-energy quark in the plasma as a function of temperature. Our study suggests that, beside $t$-channel processes, inverse Compton scattering is a relevant process for a quantitative understanding of the energy loss of an incident quark in a hot plasma.

We discuss an exact time dependent O(3) symmetric solution with a horizon of the 5d AdS classical gravity equations searching for a 4d boundary theory which would correspond to expanding gauge theory matter. The boundary energy-momentum tensor and entropy density are computed. The boundary metric is the flat Friedmann one and any time dependence on the boundary is incompatible with the Minkowski metric. At large times when curvature effects are negligible, perfect fluid behavior arises in a natural way.

Coset methods are used to construct the action describing the dynamics associated with the spontaneous breaking of the local Poincaré symmetries of $D$ dimensional space-time due to the embedding of a $p$-brane with codimension $N=D-p-1$. The resulting action is an $ISO(1,p+N)$ invariant form of the Einstein-Hilbert action, which, in addition to the gravitational vielbein, also includes $N$ massive gauge fields corresponding to the broken space translation symmetries which together carry the fundamental representation of the unbroken $SO(N)$ gauge symmetry and an $SO(N)$ Yang-Mills field localized on the brane. The long wavelength dynamics of the gravitating $p$-brane is the same as the action of an $SO(N)$ vector massive Proca field and a non-Abelian $SO(N)$ Yang-Mills field all coupled to gravity in $d=(1+p)$ dimensional space-time. The general results are specialized to determine the effective action for the gravitating vortex solution in the $D=6$ Abelian Higgs-Kibble model.

We discuss renormalization effects on neutrino masses and mixing angles in a supersymmetric string-inspired $\mathrm{SU}(4)\times \mathrm{SU}(2{)}_L\times \mathrm{SU}(2{)}_R\times \mathrm{U}(1{)}_X$ model, with matter in fundamental and antisymmetric tensor representations and singlet Higgs fields charged under the anomalous $\mathrm{U}(1{)}_X$ family symmetry. The quark, lepton and neutrino Yukawa matrices are distinguished by different Clebsch-Gordan coefficients. The presence of a second $\mathrm{U}(1{)}_X$ breaking singlet with fractional charge allows a more realistic, hierarchical light neutrino mass spectrum with bi-large mixing. By numerical investigation we find a region in the model parameter space where the neutrino mass-squared differences and mixing angles at low energy are consistent with experimental data.

The gravitational action of the smooth energy-matter components filling in the universe can affect the orbit of a planetary system. Changes are related to the acceleration of the cosmological scale size $R$. In a universe with significant dark matter, a gravitational system expands or contracts according to the amount and equation of state of the dark energy. At present time, the Solar System, according to the $\Lambda \mathrm{CDM}$ scenario emerging from observational cosmology, should be expanding if we consider only the effect of the cosmological background. Its fate is determined by the equation of state of the dark energy alone. The mean motion and periastron precession of a planet are directly sensitive to $\ddot{R}/R$, whereas variations with time in the semimajor axis and eccentricity are related to its time variation. Actual bounds on the cosmological deceleration parameters $q_0$ from accurate astrometric data of perihelion precession and changes in the third Kepler’s law in the Solar System fall short of 10 orders of magnitude with respect to estimates from observational cosmology. Future radio-ranging measurements of outer planets could improve actual bounds by 5 orders of magnitude.

The origin of the cosmic gamma-ray background (CGB) is a longstanding mystery in high-energy astrophysics. Possible candidates include ordinary astrophysical objects such as unresolved blazars, as well as more exotic processes such as dark matter annihilation. While it would be difficult to distinguish them from the mean intensity data alone, one can use anisotropy data instead. We investigate the CGB anisotropy both from unresolved blazars and dark matter annihilation (including contributions from dark matter substructures), and we find that the angular power spectra from these sources are very different. We then focus on detectability of dark matter annihilation signals using the anisotropy data by treating the unresolved blazar component as a known background. We find that the dark matter signature should be detectable in the angular power spectrum of the CGB from two-year all-sky observations with the Gamma Ray Large Area Space Telescope (GLAST), as long as the dark matter annihilation contributes to a reasonable fraction, e.g., $\gtrsim 0.3$, of the CGB at around 10 GeV. We conclude that the anisotropy measurement of the CGB with GLAST should be a powerful tool for revealing the CGB origin, and potentially for the first detection of dark matter annihilation.

The phase-integral approximation devised by Fröman and Fröman, is used for computing cosmological perturbations in the power-law inflationary model. The phase-integral formulas for the scalar and tensor power spectra are explicitly obtained up to ninth-order of the phase-integral approximation. We show that, the phase-integral approximation exactly reproduces the shape of the power spectra for scalar and tensor perturbations as well as the spectral indices. We compare the accuracy of the phase-integral approximation with the results for the power spectrum obtained with the slow-roll and uniform-approximation methods.

It is shown that, when $f^{\prime \prime }\ne 0$, metric $f(R)$ gravity is completely equivalent to an $\omega =0$ scalar-tensor theory with respect to perturbations of de Sitter space, contrary to previous expectations. Moreover, the stability conditions of de Sitter space with respect to homogeneous and inhomogeneous perturbations coincide in most scalar-tensor theories, as is the case in metric $f(R)$ gravity.

Nonanticommutativity in an open super string moving in the presence of a background antisymmetric tensor field ${\mathcal{B}}_{\mu \nu }$ is investigated in a conformal field theoretic approach, leading to nonanticommutative structures. In contrast to several discussions, in which boundary conditions are taken as Dirac constraints, we first obtain the mode algebra by using the newly proposed normal ordering, which satisfies both equations of motion and boundary conditions. Using these the anticommutator among the fermionic string coordinates is obtained. Interestingly, in contrast to the bosonic case, this new normal ordering plays an important role in uncovering the underlying nonanticommutative structure between the fermionic string coordinates. We feel that our approach is more transparent than the previous ones and the results we obtain match with the existing results in the literature.

We use the “moving puncture” approach to perform fully nonlinear evolutions of spinning quasicircular black-hole binaries with individual spins unaligned with the orbital angular momentum. We evolve configurations with the individual spins (parallel and equal in magnitude) pointing in the orbital plane and 45° above the orbital plane. We introduce a technique to measure the spin direction and track the precession of the spin during the merger, as well as measure the spin flip in the remnant horizon. The former configuration completes 1.75 orbits before merging, with the spin precessing by 98° and the final remnant horizon spin flipped by $\sim 72°$ with respect to the component spins. The latter configuration completes 2.25 orbits, with the spins precessing by 151° and the final remnant horizon spin flipped $\sim 34°$ with respect to the component spins. These simulations show for the first time how the spins are reoriented during the final stage of black-hole-binary mergers verifying the hypothesis of the spin-flip phenomenon. We also compute the track of the holes before merger and observe a precession of the orbital plane with frequency similar to the orbital frequency and amplitude increasing with time.

A scalar field with a modified dispersion relation may seed, under certain conditions, the primordial perturbations during a decelerated expansion. In this paper we examine whether and how these perturbations can be responsible for the structure formation of the observable universe. We discuss relevant difficulties and possible solutions.

The relation between the results of cosmological $N$-body simulations, and the continuum theoretical models they simulate, is currently not understood in a way which allows a quantification of $N$ dependent effects. In this first of a series of papers on this issue, we consider the quantification of such effects in the initial conditions of such simulations. A general formalism developed in [A. Gabrielli, Phys. Rev. E 70, 066131 (2004).] allows us to write down an exact expression for the power spectrum of the point distributions generated by the standard algorithm for generating such initial conditions. Expanded perturbatively in the amplitude of the input (i.e. theoretical, continuum) power spectrum, we obtain at linear order the input power spectrum, plus two terms which arise from discreteness and contribute at large wave numbers. For cosmological type power spectra, one obtains as expected, the input spectrum for wave numbers $k$ smaller than that characteristic of the discreteness. The comparison of real space correlation properties is more subtle because the discreteness corrections are not as strongly localized in real space. For cosmological type spectra the theoretical mass variance in spheres and two-point correlation function are well approximated above a finite distance. For typical initial amplitudes this distance is a few times the interparticle distance, but it diverges as this amplitude (or, equivalently, the initial redshift of the cosmological simulation) goes to zero, at fixed particle density. We discuss briefly the physical significance of these discreteness terms in the initial conditions, in particular, with respect to the definition of the continuum limit of $N$-body simulations.

We investigate quartification models in five dimensions, with the fifth dimension forming an $S^1/Z_2\times Z_2^{\prime }$ orbifold. The orbifold construction is combined with a boundary Higgs sector to break the quartified gauge group directly to a group $H\subset SU(3{)}^4$ which is operative at the electroweak scale. We consider $H=G_{\mathrm{SM}}\otimes SU(2{)}_{\ell }$ and $H=G_{\mathrm{SM}}$, where $G_{\mathrm{SM}}$ is the standard model gauge group, and find that unification occurs only when the remnant leptonic color symmetry $SU(2{)}_{\ell }$ remains unbroken. Furthermore, the demands of a realistic low-energy fermion spectrum specify a unique symmetry breaking route for the unifying case of $H=G_{\mathrm{SM}}\otimes SU(2{)}_{\ell }$. We contrast this with four-dimensional quartification models where unification may be achieved via a number of different symmetry breaking routes both with and without the remnant $SU(2{)}_{\ell }$ symmetry. The boundary Higgs sector of our model may be decoupled to achieve a Higgsless limit, and we show that the electroweak Higgs doublet may be identified as the fifth component of a higher-dimensional gauge field.

New data sets have recently become available for neutrino and antineutrino deep inelastic scattering on nuclear targets and for inclusive dimuon production in $pp$ and $pd$ interactions. These data sets are sensitive to different combinations of parton distribution functions in the large-$x$ region and, therefore, provide different constraints when incorporated into global parton distribution function fits. We compare and contrast the effects of these new data on parton distribution fits, with special emphasis on the effects at large $x$. The effects of the use of nuclear targets in the neutrino and antineutrino data sets are also investigated.

We investigate the charm sector of the nucleon structure phenomenologically, using the most up-to-date global QCD analysis. Going beyond the common assumption of purely radiatively generated charm, we explore possible degrees of freedom in the parton parameter space associated with nonperturbative (intrinsic) charm in the nucleon. Specifically, we explore the limits that can be placed on the intrinsic charm (IC) component, using all relevant hard-scattering data, according to scenarios in which the IC has a form predicted by light-cone wave function models; or a form similar to the light sea-quark distributions. We find that the range of IC is constrained to be from zero (no IC) to a level 2–3 times larger than previous model estimates. The behaviors of typical charm distributions within this range are described, and their implications for hadron collider phenomenology are briefly discussed.

Electric and color neutral solutions, and the critical conditions for the formation of gapless color superconductors, are investigated in $K^0$ condensed color-flavor locked quark matter for nonzero strange quark mass. We show that as the strange quark mass increases, gapless modes for up-strange quark pairing occur first, followed by down-strange quark pairing. The behavior of the gaps, the dispersion relations, and the thermodynamic potential are all found as functions of the strange quark mass on the basis of a Nambu–Jona-Lasinio type model. To a high degree of accuracy, they are presented as relatively simple elementary functions. This allows for easy computation for any reasonable range of baryon chemical potential and strange quark mass.

Using data from the FOCUS (E831) experiment at Fermilab, we present new measurements for the Cabibbo-suppressed decay mode $D^0\to {\pi }^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+}$. We measure the branching ratio $\Gamma (D^0\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-})/\Gamma (D^0\to K^{-}{\pi }^{+}{\pi }^{-}{\pi }^{+})=0.0914\pm 0.0018\pm 0.0022$. An amplitude analysis has been performed, a first for this channel, in order to determine the resonant substructure of this decay mode. The dominant component is the decay $D^0\to a_1(1260{)}^{+}{\pi }^{-}$, accounting for 60% of the decay rate. The second most dominant contribution comes from the decay $D^0\to \rho (770{)}^0\rho (770{)}^0$, with a fraction of 25%. We also study the $a_1(1260)$ line shape and resonant substructure. Using the helicity formalism for the angular distribution of the decay $D^0\to \rho (770{)}^0\rho (770{)}^0$, we measure a longitudinal polarization of $P_L=(71\pm 4\pm 2)\%$.

The cross section for process $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}\gamma$ in the framework of noncommutative quantum electrodynamics (NC QED) is studied. It is shown that the NC correction of scattering sections is not monotonous enhancement with total energy of colliding electrons, but there is an optimal collision energy to get the greatest NC correction. Moreover, there is a linear relation between NC QED scale energy and the optimal collision energy. The experimental methods to improve the precision of determining NC effects are discussed, because this process is an $\mathcal{O}({\alpha }^3)$ NC QED process, high precision tests are necessary.

Recently, Hawking radiation from a Schwarzschild-type black hole via a gravitational anomaly at the horizon has been derived by Robinson and Wilczek. Their result shows that, in order to demand general coordinate covariance at the quantum level to hold in the effective theory, the flux of the energy-momentum tensor required to cancel the gravitational anomaly at the horizon of the black hole is exactly equal to that of $(1+1)$-dimensional blackbody radiation at the Hawking temperature. In this paper, we attempt to apply the analysis to derive Hawking radiation from the event horizons of static, spherically symmetric dilatonic black holes with arbitrary coupling constant $\alpha$, and that from the rotating Kaluza-Klein ($\alpha =\sqrt{3}$) as well as the Kerr-Sen ($\alpha =1$) black holes via an anomalous point of view. Our results support Robinson and Wilczek’s opinion. In addition, the properties of the obtained physical quantities near the extreme limit are qualitatively discussed.

The effect of the massless gravitational scalar field assumed to couple directly to the Maxwell field on the solar-system experiments is estimated. We start with discussing the theoretical significance of this coupling. Rather disappointingly, however, we find that the scalar-field parameters never affect the observation in the limit of geometric optics, indicating a marked difference from the well-known contribution through the spacetime metric.