In a recent paper we considered the possibility of a scalar field providing an explanation for the cosmic acceleration. Our model had the interesting properties of attractorlike behavior and having its parameters of $O\left(1\right)\mathrm{}$ in Planck units. Here we discuss the effect of the field on large scale structure and CMB anisotropies. We show how some versions of our model inspired by “brane” physics have novel features due to the fact that the scalar field has a significant role over a wider range of redshifts than for typical “dark energy” models. One of these features is the additional suppression of the formation of the large scale structure, as compared with cosmological constant models. In light of the new pressures being placed on cosmological parameters (in particulr $H_0)$ by CMB data, this added suppression allows our “brane” models to give excellent fits to both CMB and large scale structure data.

The hot gas embedded in the large-scale structures in the Universe produces secondary fluctuations in the cosmic microwave background (CMB). Because it is proportional to the gas pressure integrated along the line of sight, this effect, the thermal Sunyaev-Zel’dovich (SZ) effect, provides a direct measure of large-scale structure and of cosmological parameters. We study the statistical properties of this effect using both hydrodynamical simulations and analytical predictions from an extended halo model. The adaptive mesh refinement scheme, used in the newly developed code RAMSES, provides a dynamic range of almost 4 order of magnitudes, and thus allows us to significantly improve upon earlier grid-based calculations and match the resolution reached by the latest particle-based simulations. After accounting for the finite mass resolution and box size of the simulation, we find that the halo model agrees well with the simulations. We discuss and quantify the uncertainty in both methods, and thus derive an accurate prediction for the SZ power spectrum in the ${10}^2\lesssim l\lesssim {10}^5$ range of multipole. We show how this combined analytical and numerical approach is essential for accuracy, and useful for the understanding of the physical processes and scales which contribute to large-scale SZ anisotropies.

Extra-dimensional theories contain a number of almost degenerate states at each Kaluza-Klein level. If extra dimensional momentum is at least approximately conserved then the phenomenology of such nearly degenerate states depends crucially on the mass splittings between KK modes. We calculate the complete one-loop radiative corrections to KK masses in general 5 and 6 dimensional theories. We apply our formulas to the example of universal extra dimensions and show that the radiative corrections are essential to any meaningful study of the phenomenology. Our calculations demonstrate that Feynman diagrams with loops wrapping the extra dimensions are well-defined and cutoff independent even though higher dimensional theories are not renormalizable.

We simulate lattice QCD with dynamical u and d quarks at finite chemical potential, ${\mu }_I,$ for the third component of isospin ${(I}_3)$ at both zero and at finite temperature. At zero temperature there is some ${\mu }_I,$ ${\mu }_c$ say, above which $I_3$ and parity are spontaneously broken by a charged pion condensate. This is in qualitative agreement with the prediction of effective (chiral) Lagrangians which also predict ${\mu }_c{=m}_{\pi }.$ This transition appears to be second order, with scaling properties consistent with the mean-field predictions of such effective Lagrangian models. We have also studied the restoration of $I_3$ symmetry at high temperature for ${\mu }_I>{\mu }_c.$ For ${\mu }_I$ sufficiently large, this finite temperature phase transition is very abrupt, suggesting that it is first order. As ${\mu }_I$ is decreased it appears to become second order connecting continuously with the zero temperature transition.

In the kinematical region where the center of mass energy is much larger than all other scales, the Drell-Yan process can be formulated in the target rest frame in terms of the same color dipole cross section as low Bjorken-$x$ deep inelastic scattering. Since the mechanisms for heavy dilepton production appear very different in the dipole approach and in the conventional parton model, one may wonder whether these two formulations really represent the same physics. We perform a comparison of numerical calculations in the color dipole approach with calculations in the next-to-leading order parton model. For proton-proton scattering, the results are very similar at low $x_2$ from fixed target to Relativistic Heavy Ion Collider (RHIC) energies, confirming the close connection between these two very different approaches. We also compare the transverse momentum distributions of Drell-Yan dileptons predicted in both formulations. The range of applicability of the dipole formulation and the impact of future Drell-Yan data from RHIC for determining the color dipole cross section are discussed. A detailed derivation of the dipole formulation of the Drell-Yan process is also included.

We propose to use rich information on $\pi p$ total cross sections below $N\left(\sim 10\hspace{0.5em}\mathrm{GeV}\right)$ in addition to high-energy data in order to discern whether these cross sections increase like $\log \nu$ or $(\log \nu {)}^2$ at high energies, since it is difficult to discriminate between asymptotic $\log \nu$ and $(\log \nu {)}^2$ fits from high-energy data alone. A finite-energy sum rule (FESR) which is derived in the spirit of the $P^{\prime }$ sum rule as well as the $n=1\mathrm{}$ moment FESR is required to constrain the high-energy parameters. We then search for the best fit of ${\sigma }_{\mathrm{tot}}^{\mathrm{}(+)\mathrm{}}$ above 70 GeV in terms of high-energy parameters constrained by these two FESR’s. We can show from this analysis that the $(\log \nu {)}^2$ behavior is preferred to the $\log \nu$ behavior.

We study the signal and backgrounds for the process $t\overline{t}h,\overrightarrow{h}{W}^{+}{W}^{-}$ at the CERN Large Hadron Collider (LHC) and a 100 TeV Very Large Hadron Collider (VLHC). Signals are studied in two-, three-, and four-lepton final states. We find a statistical uncertainty in the top-quark Yukawa coupling at the LHC of $16\%,8\%,12\%$ for $m_h=130,160,190\mathrm{}\hspace{0.5em}\mathrm{GeV},$ respectively. The statistical uncertainty at the VLHC is likely to be negligible in comparison with the systematic uncertainty.

We present new measurements of branching fractions for the color-favored decays $B^{-}\to D^0{\pi }^{-}$ and $B^0\to D^{+}{\pi }^{-}.$ Using $9.67\times {10}^{6}B\overline{B}$ pairs collected with the CLEO detector, we obtain the branching fractions $\mathcal{B}{(B}^{-}\to D^0{\pi }^{-})=(49.7\mathrm{}\pm 1.2\pm 2.9\pm 2.2)\times {10}^{-4}$ and $\mathcal{B}(B^0\to D^{+}{\pi }^{-})=(26.8\mathrm{}\pm 1.2\pm 2.4\pm 1.2)\times {10}^{-4}.$ The first error is statistical, the second is systematic, and the third is due to the experimental uncertainty on the production ratio of charged and neutral B mesons in ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ decays. These results, together with the current world average for the color-suppressed branching fraction $\mathcal{B}(B^0\to D^0{\pi }^0),$ are used to determine the cosine of the strong phase difference ${\delta }_I$ between the $I=1/2\mathrm{}$ and $I=3/2\mathrm{}$ isospin amplitudes. We find $\cos {\delta }_I{=0.863\mathrm{}}_{-0.023-0.035-0.030}^{+0.024+0.036+0.038\mathrm{}},$ and obtain a $90\%$ confidence interval of $16.5°<{\delta }_I<38.1\mathrm{}°.$ This nonzero value of ${\delta }_I$ suggests the presence of final state interactions in the $D\pi$ system.

Light-front (LF) quantization in the light-cone (LC) gauge is used to construct a renormalizable theory of the standard model. The framework derived earlier for QCD is extended to the Glashow-Weinberg-Salam (GWS) model of electroweak interaction theory. The Lorentz condition is automatically satisfied in LF-quantized QCD in the LC gauge for the free massless gauge field. In the GWS model, with the spontaneous symmetry breaking present, we find that the ’t Hooft condition accompanies the LC gauge condition corresponding to the massive vector boson. The two transverse polarization vectors for the massive vector boson may be chosen to be the same as found in QCD. The nontransverse and linearly independent third polarization vector is found to be parallel to the gauge direction. The corresponding sum over polarizations in the standard model, indicated by $K_{\mu \nu }\mathrm{}\left(k\right),$ has several simplifying properties similar to the polarization sum $D_{\mu \nu }\mathrm{}\left(k\right)\mathrm{}$ in QCD. The framework is unitary and ghost free (except for the ghosts at $k^{+}=0\mathrm{}$ associated with the light-cone gauge prescription). The massive gauge field propagator has well-behaved asymptotic behavior. The interaction Hamiltonian of electroweak theory can be expressed in a form resembling that of covariant theory, plus additional instantaneous interactions which can be treated systematically. The LF formulation also provides a transparent discussion of the Goldstone boson (or electroweak) equivalence theorem, as the illustrations show.

The possibility of detecting noncommutative space relics is analyzed using the Aharonov-Bohm effect. We show that, if space is noncommutative, the holonomy receives nontrivial kinematical corrections that will produce a diffraction pattern even when the magnetic flux is quantized. The scattering problem is also formulated, and the differential cross section is calculated. Our results can be extrapolated to high energy physics and the bound $\theta \sim [10\hspace{0.5em}\mathrm{TeV}{]}^{-2}$ is found. If this bound holds, then noncommutative effects could be explored in scattering experiments measuring differential cross sections for small angles. The bound state Aharonov-Bohm effect is also discussed.

The thermodynamics of five-dimensional Schwarzschild anti–de Sitter (SAdS) and SdS black holes (BHs) in the particular model of higher derivative gravity is considered. The free energy, mass (thermodynamical energy) and entropy are evaluated. A parameter region exists where BH entropy is zero or negative. Arguments are given that the corresponding BH solutions are not stable. We also present the Friedmann-Robertson-Walker (FRW) equations of motion of time- (space-)like branes in SAdS or SdS BH backgrounds. The properties of dual conformal field theory (CFT) are discussed and it is shown that it has a zero Casimir energy when BH entropy (effective gravitational constant) is zero. The Cardy-Verlinde formula for CFT dual to a SAdS or SdS BH is found in a universal form.

We investigate the classical formation of a D-dimensional black hole in a high-energy collision of two particles. The existence of an apparent horizon is related to the solution of an unusual boundary-value problem for Poisson’s equation in flat space. For a sufficiently small impact parameter, we construct solutions giving such apparent horizons in $D=4.\mathrm{}$ These supply improved estimates of the classical cross section for black hole production, and of the mass of the resulting black holes. We also argue that a horizon can be found in a region of weak curvature, suggesting that these solutions are valid starting points for a semiclassical analysis of quantum black hole formation.

The different definitions for the equation of state of a nonminimally coupled scalar field that have been introduced in the literature are analyzed. Particular emphasis is made upon those features that could yield an observable way of distinguishing nonminimally coupled theories from general relativity, with the same or with alternate potentials. It is found that some earlier claims that superquintessence, a stage of superaccelerated expansion of the universe, is possible within realistic nonminimally coupled theories are the result of an arguable definition of the equation of state. In particular, it is shown that these previous results do not import any observable consequence, i.e., that the theories are observationally identical to general relativity models and that superquintessence is not more than a mathematical outcome. Finally, in the case of nonminimally coupled theories with coupling $F=1+\xi {\phi }^2$ and tracking potentials, it is shown that no superquintessence is possible.

We analyze the observational constraints on brane-world cosmology whereby the universe is described as a three-brane embedded in a five-dimensional anti–de Sitter space. In this brane-universe cosmology, the Friedmann equation is modified by the appearance of extra terms which derive from the existence of the extra dimensions. In the present work we concentrate on the “dark radiation” term which diminishes with the cosmic scale factor as $a^{-4}.$ We show that, although the observational constraints from primordial abundances allow only a small contribution when this term is positive, a much wider range of negative values is allowed. Furthermore, such a negative contribution can reconcile the tension between the observed primordial ${}^4\mathrm{He}$ and D abundances. We also discuss the possible constraints on this term from the power spectrum of CMB anisotropies in the limit of negligible cosmological perturbation on the brane world. We show that BBN limits the possible contribution from dark radiation just before the $e^{+}{e}^{-}$ annihilation epoch to lie between -123% and +11% of the background photon energy density. Combining this with the CMB constraint reduces this range to between -41% and +10.5% at the $2\sigma$ confidence level.

A first principles derivation is given of the neutrino damping rate in real-time thermal field theory. Starting from the discontinuity of the neutrino self-energy at the two loop level, the damping rate can be expressed as integrals over phase space of amplitudes squared, weighted with statistical factors that account for the possibility of particle absorption or emission from the medium. Specific results for a background composed of neutrinos, leptons, protons, and neutrons are given. Additionally, for the real part of the dispersion relation we discuss the relation between the results obtained from the thermal field theory and those obtained by the thermal average of the forward scattering amplitude.

It is often the case in numerical relativity that schemes that are known to be convergent for well posed systems are used in evolutions of weakly hyperbolic formulations of Einstein’s equations. Here we explicitly show that with several of the discretizations that have been used throughout the years, this procedure leads to nonconvergent schemes. That is, arbitrarily small initial errors are amplified without bound when resolution is increased, independently of the amount of numerical dissipation introduced. The lack of convergence introduced by this instability can be particularly subtle, in the sense that it can be missed by several convergence tests, especially in $\mathrm{}(3+1)\mathrm{}$-dimensional codes. We propose tests and methods to analyze convergence that may help detect these situations.

We consider forced tunneling in QCD, described semiclassically by instanton–anti-instanton field configurations. By separating topologically different minima we obtain details of the effective potential and study the turning states, which are similar to the sphaleron solution in electroweak theory. These states are alternatively derived as minima of the energy under the constraints of fixed size and Chern-Simons number. We study, both analytically and numerically, the subsequent evolution of such states by solving the classical Yang-Mills equations in real time, and find that the gauge field strength is quickly localized into an expanding shell of radiating gluons. The relevance to high-energy collisions of hadrons and nuclei is briefly discussed.

We compute the chiral corrections to octet baryon axial vector currents through $\mathcal{O}{(p}^3)$ in heavy baryon chiral perturbation theory, including both octet and decuplet baryon intermediate states. We include the latter in a consistent way by using the small scale expansion. We find that, in contrast to the situation at $\mathcal{O}{(p}^2),$ there exist no cancellations between octet and decuplet contributions at $\mathcal{O}{(p}^3).\mathrm{}$ Consequently, the $\mathcal{O}{(p}^3)$ corrections spoil the expected scaling behavior of the chiral expansion. We discuss this result in terms of the ${1/N}_c$ expansion. We also consider the implications for the determination of the strange quark contribution to the nucleon spin from polarized deep inelastic scattering data.

We discuss deep inelastic scattering at high energies as a critical phenomenon in $2+1$ space-time dimensions. In the limit of Bjorken $\overrightarrow{x}0,$ QCD SU(3) with quark fields becomes a critical theory with a diverging correlation length $\xi \mathrm{}\left(x\right)\mathrm{}\propto x^{-1/2{\lambda }_2}$ where the exponent ${\lambda }_2=2.52\mathrm{}$ is obtained from the center group Z(3) of SU(3). We conjecture that the dipole wave function of the virtual photon for transverse sizes $1/Q<\mathrm{}{x}_{\perp }<\xi$ obeys a correlation scaling $\Psi \propto {(x}_{\perp }{)}^{-\mathrm{}(1+n)\mathrm{}}$ before exponentially decaying for distances larger than the correlation length. Using this behavior combined with different x-independent dipole proton cross sections we calculate the proton structure function and compare it with the experimental data. We take the good agreement with the measured proton structure function ${\mathrm{F}}_2{(x,Q}^2)$ as an indication that at high energies dimensional reduction to an effective three dimensional theory with a critical point occurs.

We consider nonresonant contributions in the Dalitz-plot analysis of $\overrightarrow{B}\rho \overrightarrow{\pi }{\pi }^{+}{\pi }^{-}{\pi }^0$ decay and their potential impact on the extraction of the Cabibbo-Kobayashi-Maskawa parameter $\alpha .$ In particular, we examine the role of the heavy mesons $B^{*}$ and $B_0,$ via the process $\overrightarrow{B}\pi {(B}^{*}{,B}_0)\to {\pi }^{+}{\pi }^{-}{\pi }^0,$ and their interference with resonant contributions in the $\rho$-mass region. We discuss the inherent uncertainties and suggest that the effects may be substantially smaller than previously indicated.