New, radiatively generated, leading order (LO) quark $\mathrm{}(u,d,s,c,b)\mathrm{}$ and gluon densities in a real, unpolarized photon are presented. We perform a global 3-parameter fit, based on LO Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations, to all available data for the structure function $F_2^{\gamma }{(x,Q}^2).\mathrm{}$ We adopt a new theoretical approach called ACOT(χ), originally introduced for the proton, to deal with the heavy-quark thresholds. This defines our basic model [Cornet-Jankowski-Krawczyk-Lorca (CJKL) model], which gives a very good description of the experimental data on $F_2^{\gamma }{(x,Q}^2),$ for both $Q^2$ and x dependences. For comparison we perform a standard fit using the fixed flavor-number scheme $({\mathrm{FFNS}}_{\mathrm{CJKL}}$ model), updated with respect to the previous fits of this type. We show the superiority of the CJKL fit over the ${\mathrm{FFNS}}_{\mathrm{CJKL}}$ one and other LO fits to the $F_2^{\gamma }{(x,Q}^2)$ data. The CJKL model gives also the best description of the CERN LEP data on the $Q^2$ dependence of the $F_2^{\gamma },$ averaged over various x regions, and the $F_{2,c}^{\gamma },$ which were not used directly in the fit. Finally, a simple analytic parametrization of the resulting parton densities obtained with the CJKL model is given.

We briefly discuss the predictions of the heavy quark effective theory for the semileptonic decays of a heavy pseudoscalar to a light one, or to a light vector meson. We point out that measurement of combinations of differential helicity decay rates at CLEO-c and the B factories can provide a model independent means of extracting the ratio $|V_{\mathrm{ub}}|/|V_{\mathrm{cd}}|.$ We briefly discuss the corrections to this prediction.

Integrating out fast varying quantum fluctuations about Yang-Mills fields $A_i$ and $A_4,$ we arrive at the effective action for those fields at high temperatures. Assuming that the fields $A_i$ and $A_4$ are slowly varying but that the amplitude of $A_4$ is arbitrary, we find a nontrivial effective gauge invariant action both in the electric and magnetic sectors. Our results can be used for studying correlation functions at high temperatures beyond the dimensional reduction approximation, as well as for estimating quantum weights of classical static configurations such as dyons.

The successive perturbative estimates of the pressure of QCD at high temperature T show no sign of convergence, unless the coupling constant g is unrealistically small. Exploiting known results of an effective field theory which separates hard (order $2\pi T)$ and soft (order $gT)$ contributions, we explore the accuracy of simple resummations which at a given loop order systematically treat hard contributions strictly perturbatively, but soft contributions without truncations. This turns out to improve significantly the two-loop and the three-loop results in that both remain below the ideal-gas value, and the degree of renormalization scale dependence decreases as one goes from two to three loop order, whereas it increases in the conventional perturbative results. Including the four-loop logarithms recently obtained by Kajantie et al., we find that this trend continues and that with a particular sublogarithmic constant the untruncated four-loop result is close to the three-loop result, which itself agrees well with available lattice results down to temperatures of about ${2.5T}_c.$ We also investigate the possibility of optimization by using a variational (“screened”) perturbation theory in the effective theory. At two loops, this gives a result below the ideal gas value and also closer to lattice results than the recent two-loop hard-thermal-loop-screened result of Andersen et al. While at three-loop order the gap equation of dimensionally reduced screened perturbation theory does not have a solution in QCD, this is remedied upon inclusion of the four-loop logarithms.

We examine the gravitational collapse of sphaleron type configurations in the Einstein-Yang-Mills-Higgs theory. Working in spherical symmetry, we investigate the critical behavior in this model. We provide evidence that for various initial configurations, there can be three different critical transitions between possible end states with different critical solutions sitting on the threshold between these outcomes. In addition, we show that within the dispersive and black hole regimes there are new possible end states: namely, a stable, regular sphaleron and a stable, hairy black hole.

We consider a braneworld inflation model driven by the dynamics of a scalar field living in the 5-dimensional bulk, the so-called “bulk inflaton model,” and investigate the geometry in the bulk and large scale cosmological perturbations on the brane. The bulk gravitational effects on the brane are described by a projection of the 5-dimensional Weyl tensor, which we denote by $E_{\mu \nu }.$ Focusing on a tachyonic potential model, we take a perturbative approach in the anti–de Sitter $\left({\mathrm{AdS}}_5\right)$ background with a single de Sitter brane. We first formulate the evolution equations for $E_{\mu \nu }$ in the bulk. Next, applying them to the case of a spatially homogeneous brane, we obtain two different integral expressions for $E_{\mu \nu }.$ One of them reduces to the expression obtained previously when evaluated on the brane. The other is a new expression that may be useful for analyzing the bulk geometry. Then we consider superhorizon scale cosmological perturbations and evaluate the bulk effects onto the brane. In the limit $H^2{\mathcal{l}}^2\ll 1,$ where H is the Hubble parameter on the brane and $\mathcal{l}$ is the bulk curvature radius, we find that the effective theory on the brane is identical to the 4-dimensional Einstein-scalar theory with a simple rescaling of the potential even under the presence of inhomogeneities. In particular, it is found that the anticipated nontrivial bulk effect due to the spatially anisotropic part of $E_{\mu \nu }$ may appear only at ${O(H}^4{\mathcal{l}}^4).\mathrm{}$

We treat the two-dimensional Achucarro-Ortiz black hole (also known as a $1+1$ dilatonic black hole) as a Casimir-type system. The stress tensor of a massless scalar field satisfying Dirichlet boundary conditions on two one-dimensional “walls” (“Dirichlet walls”) is explicitly calculated in three different vacua. Without employing known regularization techniques, the expression in each vacuum for the stress tensor is reached by using Wald’s axioms. Finally, within this asymptotically nonflat gravitational background, it is shown that the equilibrium of the configurations, obtained by setting the Casimir force to zero, is controlled by the cosmological constant.

A brane evolving in the background of a charged AdS black hole displays in general a bouncing behavior with a smooth transition from a contracting to an expanding phase. We examine in detail the conditions and consequences of this behavior in various cases. For a cosmological-constant-dominated brane, we obtain a singularity-free, inflationary era which is shown to be compatible only with an intermediate-scale fundamental Planck mass. For a radiation-dominated brane, the bouncing behavior can occur only for background-charge values exceeding those allowed for non-extremal black holes. For a matter-dominated brane, the black-hole mass affects the proper volume or the expansion rate of the brane. We also consider the brane evolving in an asymmetric background of two distinct charged AdS black hole spacetimes being bounded by the brane and find that, in the case of an empty critical brane, bouncing behavior occurs only if the black-hole mass difference is smaller than a certain value. The effects of a brane curvature term on the bounce at early and late times are also investigated.

Dwarf spiral galaxies, and in particular the prototypical DDO 154, are known to be completely dominated by an unseen component. The putative neutralinos, so far the favored explanation for the astronomical dark matter, fail to reproduce the well measured rotation curves of those systems because these species tend to form a central cusp whose presence is not supported by observation. We have considered here a self-coupled charged scalar field as an alternative to neutralinos and investigated whether a Bose condensate of that field could account for the dark matter inside DDO 154 and more generally inside dwarf spirals. The size of the condensate turns out to be precisely determined by the scalar mass m and self-coupling $\lambda$ of the field. We find actually that for $m^4/\lambda \sim 50–75{\mathrm{eV}}^4$ the agreement with the measurements of the circular speed of DDO 154 is impressive, whereas it lessens for larger systems. The cosmological behavior of the field is also found to be consistent, though marginally, with the limits set by big bang nucleosynthesis on the effective number of neutrino families. We conclude that classical configurations of a scalar and self-coupled field provide a possible solution to the astronomical dark matter problem and we suggest further directions of research.

The equation of state characterizing the dark energy component is constrained by combining Chandra observations of the x-ray luminosity of galaxy clusters with independent measurements of the baryonic matter density and the latest measurements of the Hubble parameter as given by the HST key project. By assuming a spatially flat scenario driven by a “quintessence” component with an equation of state $p_x=\omega {\rho }_x,$ we place the following limits on the cosmological parameters $\omega$ and ${\Omega }_{\mathrm{m}}:$ (i) $-1<~\omega <~-0.55$ and ${\Omega }_{\mathrm{m}}{=0.32\mathrm{}}_{-0.014}^{+0.027\mathrm{}}$ $\left(1\mathrm{}\sigma \right)$ if the equation of state of the dark energy is restricted to the interval $-1<~\omega <0\mathrm{}$ (the usual quintessence) and (ii) $\omega =-{1.29}_{-0.792}^{+0.686\mathrm{}}$ and ${\Omega }_{\mathrm{m}}{=0.31\mathrm{}}_{-0.034}^{+0.037\mathrm{}}$ $\left(1\mathrm{}\sigma \right)$ if $\omega$ violates the null energy condition and assume values below $-1$ (extended quintessence or “phantom” energy). These results are in good agreement with independent studies based on supernovae observations, large-scale structure, and the anisotropies of the cosmic background radiation.

Models of dark energy are conveniently characterized by the equation-of-state parameter $w=p/\rho ,$ where $\rho$ is the energy density and p is the pressure. Imposing the dominant energy condition, which guarantees stability of the theory, implies that $w>~-1.$ Nevertheless, it is conceivable that a well-defined model could (perhaps temporarily) have $w<\mathrm{}-1\hspace{0.5em},$ and indeed such models have been proposed. We study the stability of dynamical models exhibiting $w<\mathrm{}-1$ by virtue of a negative kinetic term. Although naively unstable, we explore the possibility that these models might be phenomenologically viable if thought of as effective field theories valid only up to a certain momentum cutoff. Under our most optimistic assumptions, we argue that the instability time scale can be greater than the age of the universe, but only if the cutoff is at or below ${10}^{-3}\mathrm{eV}.$ We conclude that it is difficult, although not necessarily impossible, to construct viable models of dark energy with $w<\mathrm{}-1;$ observers should keep an open mind, but the burden is on theorists to demonstrate that any proposed new models are not ruled out by rapid vacuum decay.

We study the resonant spin-flavor (RSF) conversion of supernova neutrinos, which is induced by the interaction between the nonzero neutrino magnetic moment and the supernova magnetic fields, and its dependence on presupernova models. As the presupernova models, we adopt the latest ones by Woosley, Heger, and Weaver, and, further, models with both solar and zero metallicity are investigated. Since the $\left(1\mathrm{}-{2Y}_e\right)$ profile of the new presupernova models, which is responsible for the RSF conversion, suddenly drops at the resonance region, the completely adiabatic RSF conversion is not realized, even if ${\mu }_{\nu }{B}_0{=(10\mathrm{}}^{-12}{\mu }_B{\left)\right(10\mathrm{}}^{10}\mathrm{G}),$ where $B_0$ is the strength of the magnetic field at the surface of the iron core. In particular for the model with zero metallicity, the conversion is highly nonadiabatic in the high energy region, reflecting the $\left(1\mathrm{}-{2Y}_e\right)$ profile of the model. In calculating the flavor conversion, we find that the shock wave propagation, which changes density profiles drastically, is a much more severe problem than it is for the pure Mikheyev-Smirnov-Wolfenstein (MSW) conversion case. This is because the RSF effect occurs at a far deeper region than the MSW effect. To avoid the uncertainty concerning the shock propagation, we restrict our discussion to 0.5 s after the core bounce (and for more conservative discussion, 0.25 s), during which the shock wave is not expected to affect the RSF region. We also evaluate the energy spectrum at the Super-Kamiokande detector for various models using the calculated conversion probabilities, and find that it is very difficult to obtain useful information on the supernova metallicities and magnetic fields or on the neutrino magnetic moment from the supernova neutrino observation. Future prospects are also discussed.

We report on a search for a CP-violating asymmetry in the charmless hadronic decay $\overrightarrow{B}{K}^{*}{\mathrm{}\left(892\right)\mathrm{}}^{\pm }{\pi }^{\mp },$ using $9.1{\mathrm{fb}}^{-1}$ of integrated luminosity produced at $\sqrt{s}=10.58\mathrm{}\mathrm{GeV}$ and collected with the CLEO detector. We find ${\mathcal{A}}_{\mathrm{CP}}\left(\overrightarrow{B}{K}^{*}{\mathrm{}\left(892\right)\mathrm{}}^{\pm }{\pi }^{\mp }\right){=0.26\mathrm{}}_{-0.34}^{+0.33\mathrm{}}\left(\mathrm{stat}{)}_{-0.08}^{+0.10\mathrm{}}\right(\mathrm{syst}),$ giving an allowed interval of $[-0.31,0.78]$ at the 90% confidence level.

We investigate the muon anomalous magnetic dipole moment (MDM), the muon electric dipole moment (EDM) and the lepton-flavor-violating decays of the $\tau$ lepton, $\overrightarrow{\tau }\mu \gamma$ and $\overrightarrow{\tau }3\mu ,$ in the CP-violating minimal supersymmetric standard model with nonuniversal soft-supersymmetry breaking. We evaluate numerically the muon EDM and the branching ratios $B\left(\overrightarrow{\tau }\mu \gamma \right)$ and $B\left(\overrightarrow{\tau }3\mu \right),$ after taking into account the experimental constraints from the electron EDM and muon MDM. Upon imposition of the experimental limits on our theoretical predictions for the aforementioned branching ratios and the muon MDM, we obtain an upper bound of about ${10}^{-23}e\mathrm{cm}$ on the muon EDM which lies well within the explorable reach of the proposed experiment at BNL.

We determine $O\left(a\right)\mathrm{}$ boundary improvement coefficients up to the 1-loop level for the Schrödinger functional coupling with improved gauge actions including plaquette and rectangle loops. These coefficients are required to implement 1-loop $O\left(a\right)\mathrm{}$ improvement in full QCD simulations for the coupling with the improved gauge actions. To this order, lattice artifacts of the step scaling function for each improved gauge action are also investigated. In addition, passing through the Schrödinger functional scheme, we estimate more accurately the ratio of the $\Lambda$ parameters between the improved gauge actions and the plaquette action.

We analyze the cutoff dependence of mesonic spectral functions calculated at finite temperature on Euclidean lattices with a finite temporal extent. In the infinite temperature limit we present analytic results for lattice spectral functions calculated with standard Wilson fermions as well as a truncated perfect action. We explicitly determine the influence of “Wilson doublers” on the high momentum structure of the mesonic spectral functions and show that this cutoff effect is strongly suppressed when using an improved fermion action.

We introduce a random matrix model with the symmetries of QCD at finite temperature and chemical potentials for baryon number and isospin. We analyze the phase diagram of this model in the chemical potential plane for different temperatures and quark masses. We find a rich phase structure with five different phases separated by both first and second order lines. The phases are characterized by the pion condensate and the chiral condensate for each of the flavors. In agreement with lattice simulations, we find that in the phase with zero pion condensate the critical temperature depends in the same way on the baryon number chemical potential and on the isospin chemical potential. At nonzero quark mass, we find, remarkably, that the critical end point at nonzero temperature and baryon chemical potential is split in two by an arbitrarily small isospin chemical potential. As a consequence, there are two crossovers that separate the hadronic phase from the quark-gluon plasma phase at high temperature. Detailed analytical results are obtained at zero temperature and in the chiral limit.

We calculate the probability (“quenching weight”) that a hard parton radiates an additional energy fraction $\Delta E$ due to scattering in spatially extended QCD matter. This study is based on an exact treatment of a finite in-medium path length; it includes the case of a dynamically expanding medium, and it extends to the angular dependence of the medium-induced gluon radiation pattern. All calculations are done in the multiple soft scattering approximation [Baier-Dokshitzer-Mueller-Peigné-Schiff-Zakharov (BDMPSZ) formalism] and in the single hard scattering approximation $[N=1\mathrm{}$ opacity approximation]. By comparison, we establish a simple relation between the transport coefficient, Debye screening mass and opacity, for which both approximations lead to comparable results. Together with this paper, a CPU-inexpensive numerical subroutine for calculating quenching weights is provided electronically. To illustrate its applications, we discuss the suppression of hadronic transverse momentum spectra in nucleus-nucleus collisions. Remarkably, the kinematic constraint resulting from finite in-medium path lengths reduces significantly the $p_{\perp }$ dependence of the nuclear modification factor, thus leading to consistency with the data measured at the BNL Relativistic Heavy Ion Collider.

Recent measurements of the time-dependent CP asymmetry of the $\overrightarrow{B}\phi K_S$ decay give results whose central values differ from standard model expectations. It is shown how such data can be used to identify new physics contributions in a model-independent manner. In general, a sizable new amplitude with nontrivial weak and strong phases would be required to explain current data. An improvement in the quality of data will allow one to form a more definite conclusion.