We analyze the triviality-quantum decoherence of Euclidean quantum chromodynamics in the gauge invariant quark current sector in the presence of a very strong external white-noise electromagnetic (strength) field within the context of QCD in the ’t Hooft limit of a large number of colors.

Conformal gravity is one of the most important models of quantum gravity with higher derivatives. We investigate the role of the Gauss-Bonnet term in this theory. The coincidence limit of the second coefficient of the Schwinger-DeWitt expansion is evaluated in an arbitrary dimension n. In the limit $n=4\mathrm{}$ the Gauss-Bonnet term is topological and its contribution cancels. This cancellation provides an efficient test for the correctness of calculation and, simultaneously, clarifies the long-standing general problem concerning the role of the topological term in quantum gravity. For $n\ne 4$ the Gauss-Bonnet term becomes dynamical in the classical theory and relevant at the quantum level. In particular, the renormalization group equations in dimension $n=4\mathrm{}-\epsilon$ manifest new fixed points due to quantum effects of this term.

We study the cosmology of a general scalar field and barotropic fluid during the early stage of a brane-world where the Friedmann constraint is dominated by the square of the energy density. Assuming both the scalar field and fluid are confined to the brane, we find a range of behavior depending on the form of the potential. Generalizing an approach developed for a standard Friedmann cosmology, in [A. de la Macorra and G. Piccinelli, Phys. Rev. D 61, 123503 (2000)], we show that the potential dependence $V\left(\phi \right)$ can be described through a parameter $\lambda \equiv -\sqrt{2}{m}_5^{3/2}{V}^{\prime }/\left(\sqrt{H}V\right),$ where $m_5$ is the five-dimensional Planck mass, H is the Hubble parameter, and $V^{\prime }\equiv dV/d\phi .$ For the case where $\lambda$ asymptotes to zero, we show that the solution exhibits stable inflationary behavior. On the other hand if it approaches a finite constant, then $V\left(\phi \right)\propto 1/{\phi }^2.$ For $\overrightarrow{\lambda }\infty$ asymptotically, we find examples where it does so both with and without oscillating. In the latter case, the barotropic fluid dominates the scalar field asymptotically. Finally we point out an interesting duality that leads to identical evolution equations in the high-energy ${\rho }^2$ dominated regime and the low-energy $\rho$ dominated regime.

The evidence of the acceleration of universe at present time has led to investigate modified theories of gravity and alternative theories of gravity, which are able to explain acceleration from a theoretical viewpoint without the need of introducing dark energy. In this paper we study alternative gravitational theories defined by Lagrangians which depend on general functions of the Ricci scalar invariant in minimal interaction with matter, in view of their possible cosmological applications. Structural equations for the spacetimes described by such theories are solved and the corresponding field equations are investigated in the Palatini formalism, which prevents instability problems. Particular examples of these theories are also shown to provide, under suitable hypotheses, a coherent theoretical explanation of earlier results concerning the present acceleration of the universe and cosmological inflation. We suggest moreover a new possible Lagrangian, depending on the inverse of $\sinh \mathrm{}\left(R\right),$ which gives an explanation to the present acceleration of the universe.

The observed angular power spectrum of the cosmic microwave background temperature anisotropy, $C_l,$ is a convolution of a cosmological radiative transport kernel with an assumed primordial power spectrum of inhomogeneities. Exquisite measurements of $C_l$ over a wide range of multipoles from the Wilkinson Microwave Anisotropy Probe (WMAP) has opened up the possibility to deconvolve the primordial power spectrum for a given set of cosmological parameters (base model). We implement an improved (error sensitive) Richardson-Lucy deconvolution algorithm on the measured angular power spectrum from WMAP assuming the concordance cosmological model. The most prominent feature of the recovered $P\left(k\right)\mathrm{}$ is a sharp, infrared cutoff on the horizon scale. The resultant $C_l$ spectrum using the recovered spectrum has a likelihood far better than a scale invariant, or, “best fit” scale free spectra $(\Delta \ln \mathcal{L}\approx 25$ with respect to Harrison Zeldovich, and, $\Delta \ln \mathcal{L}\approx 11$ with respect to power law with $n_s=0.95).\mathrm{}$ The recovered $P\left(k\right)\mathrm{}$ has a localized excess just above the cutoff which leads to great improvement of likelihood over the simple monotonic forms of model infrared cutoff spectra considered in the post WMAP literature. The recovered $P\left(k\right),$ in particular, the form of infrared cutoff is robust to small changes in the cosmological parameters. We show that remarkably similar form of infrared cutoff is known to arise in very reasonable extensions and refinements of the predictions from simple inflationary scenarios. Our method can be extended to other cosmological observations such as the measured matter power spectrum and, in particular, the much awaited polarization spectrum from WMAP.

We study the cosmological consequences of generic scalar fields like moduli which decay only through gravitationally suppressed interactions. We consider a new production mechanism of gravitinos from moduli decay, which might be more effective than previously known mechanisms, and calculate the final gravitino-to-entropy ratio to compare with the constraints imposed by successful big bang nucleosynthesis (BBN) etc., taking possible hadronic decays of gravitinos into account. We find the modulus mass smaller than $\sim {10}^4\mathrm{TeV}$ is excluded. On the other hand, inflation models with high reheating temperatures $T_{R,\inf }\sim {10}^{16}\mathrm{GeV}$ can be compatible with BBN thanks to the late-time entropy production from the moduli decay if model parameters are appropriately chosen.

We revised the discussion on the degree of spin polarization of single top quarks produced via Wg fusion process in ep collision at TESLA+HERAp and CLIC+LHC energies in connection with our article in [Phys. Rev. D 69, 034016 (2004)]. For $e\overrightarrow{b}t\overline{\nu }$ subprocess we show that the top quark spin is completely polarized when the spin basis is chosen in the direction of the incoming positron beam in the rest frame of top quark. After combining properly the cross sections of $e^{+}\overrightarrow{b}t\overline{\nu }$ and $e^{+}\overrightarrow{g}t\overline{b}\overline{\nu }$ processes we find that 96% of the top quarks have their spins up in $e^{+}$-beam direction with the asymmetry of 0.92. Some of the spin fractions and asymmetries have been corrected 2–5 % when compared to the previous paper. Consequently, this Brief Report improves the results of the previous paper about the ideal basis for studying the top quark spin in ep collision.

The $K^{+}\to {\pi }^0{\pi }^0{e}^{+}\nu {(K}_{e4\mathrm{}}^{00})$ decay has been measured with stopped positive kaons for a data sample of 216 events. A comparison of the observed spectra with a Monte Carlo simulation determined the $K_{e4\mathrm{}}^{00}$ form factor. The results are compatible with the $K^{+}\to {\pi }^{+}{\pi }^{-}{e}^{+}\nu$ data, as estimated from the $\Delta I=1/2\mathrm{}$ rule. We also established that the $K_{e4\mathrm{}}^{00}$ channel can be used to determine the $\pi -\pi$ scattering lengths.

We show how transverse beam polarization at $e^{+}{e}^{-}$ colliders can provide a novel means to search for CP violation by observing the distribution of a single final-state particle without measuring its spin. We suggest an azimuthal asymmetry which singles out interference terms between standard model contribution and new-physics scalar or tensor effective interactions in the limit in which the electron mass is neglected. Such terms are inaccessible with unpolarized or longitudinally polarized beams. The asymmetry is sensitive to CP violation when the transverse polarizations of the electron and positron are in opposite senses. The sensitivity of planned future linear colliders to new-physics CP violation in $e^{+}{e}^{-}\to t\overline{t}$ is estimated in a model-independent parametrization. It would be possible to put a bound of $\sim 7\mathrm{TeV}$ on the new-physics scale $\Lambda$ at the 90% C.L. for $\sqrt{s}=500\mathrm{}\mathrm{GeV}$ and $\int \mathrm{dt}\mathcal{L}=500\mathrm{}{\mathrm{fb}}^{-1},$ with transverse polarizations of 80% and 60% for the electron and positron beams, respectively.

We extend previous analyses of the supersymmetric loop correction to the charged Higgs couplings to include the coupling $H^{\pm }{\chi }^{\mp }{\chi }^0.$ The analysis completes the previous analyses where similar corrections were computed for $H^{+}\overline{t}b$ ${(H}^{-}t\overline{b}),$ and for $H^{+}{\tau }^{-}{\overline{\nu }}_{\tau }$ ${(H}^{-}{\tau }^{+}{\nu }_{\tau })$ couplings within the minimal supersymmetric standard model. The effective one loop Lagrangian is then applied to the computation of the charged Higgs decays. The sizes of the supersymmetric loop correction on branching ratios of the charged Higgs $H^{+}{(H}^{-})$ into the decay modes $t\overline{b}$ $\left(\overline{t}b\right),$ $\overline{\tau }{\nu }_{\tau }$ $\left(\tau {\overline{\nu }}_{\tau }\right),$ and ${\chi }_i^{+}{\chi }_j^0\left({\chi }_i^{-}{\chi }_j^0\right)(i=1,2;j=1\mathrm{}–4)$ are investigated and the supersymmetric loop correction is found to be significant, i.e., in the range 20–30 % in significant regions of the parameter space. The loop correction to the decay mode ${\chi }_1^{\pm }{\chi }_2^0$ is examined in specific detail as this decay mode leads to a trileptonic signal. The effects of CP phases on the branching ratio are also investigated. A brief discussion of the implications of the analysis for colliders is given.

We examine the possibility of electroweak baryogenesis and dark matter in the nMSSM, a minimal extension of the MSSM with a singlet field. This extension avoids the usual domain wall problem of the NMSSM, and also appears as the low energy theory in models of dynamical electroweak symmetry breaking with a so-called fat-Higgs boson. We demonstrate that a strong, first order electroweak phase transition, necessary for electroweak baryogenesis, may arise in regions of parameter space where the lightest neutralino provides an acceptable dark matter candidate. We investigate the parameter space in which these two properties are fulfilled and discuss the resulting phenomenology. In particular, we show that there are always two light CP-even and one light CP-odd Higgs bosons with masses smaller than about 250 GeV. Moreover, in order to obtain a realistic relic density, the lightest neutralino mass tends to be smaller than $M_Z/2,$ in which case the lightest Higgs boson decays predominantly into neutralinos.

Using lattice quantum chromodynamics (QCD) we perform an unquenched calculation of the gluon propagator in Landau gauge. We use configurations generated with the AsqTad quark action by the MILC collaboration for the dynamical quarks and compare the gluon propagator of quenched QCD (i.e., the pure Yang-Mills gluon propagator) with that of 2+1 flavor QCD. The effects of the dynamical quarks are clearly visible and lead to a significant reduction of the nonperturbative infrared enhancement relative to the quenched case.

The decays of B mesons to a pair of charmless pseudoscalar (P) mesons are analyzed within a framework of flavor SU(3). Symmetry breaking is taken into account in tree (T) amplitudes through ratios of decay constants; exact SU(3) is assumed elsewhere. Acceptable fits to $\overrightarrow{B}\pi \pi$ and $\overrightarrow{B}K\pi$ branching ratios and CP asymmetries are obtained with tree, color-suppressed $\mathrm{}\left(C\right),$ penguin $\mathrm{}\left(P\right),$ and electroweak penguin ${(P}_{\mathrm{EW}})$ amplitudes. Crucial additional terms for describing processes involving $\eta$ and ${\eta }^{\prime }$ include a large flavor-singlet penguin amplitude (S) as proposed earlier and a penguin amplitude $P_{\mathrm{tu}}$ associated with intermediate t and u quarks. For the $B^{+}\to {\pi }^{+}{\eta }^{\prime }$ mode a term $S_{\mathrm{tu}}$ associated with intermediate t and u quarks also may be needed. Values of the weak phase $\gamma$ are obtained consistent with an earlier analysis of $\overrightarrow{B}\mathrm{VP}$ decays, where V denotes a vector meson, and with other analyses of CKM parameters.

We suggest a tetracritical fixed point to naturally occur in strongly interacting theories. As a fundamental example we analyze the temperature-quark chemical potential phase diagram of QCD with fermions in the adjoint representation of the gauge group (i.e., adjoint QCD). Here we show that such a nontrivial multicritical point exists and is due to the interplay between the spontaneous breaking of a global $U\left(1\right)\mathrm{}$ symmetry and the center group symmetry associated with confinement. Our results demonstrate that taking confinement into account is essential for understanding the critical behavior as well as the full structure of the phase diagram of adjoint QCD. This is in contrast to ordinary QCD where the center group symmetry associated with confinement is explicitly broken when the quarks are part of the theory.

We investigate the low energy phenomenology of the lighter pseudoscalar $A_1^0$ in the NMSSM. The $A_1^0$ mass can naturally be small due to a global ${U\left(1\right)\mathrm{}}_R$ symmetry of the Higgs potential, which is only broken by trilinear soft terms. The $A_1^0$ mass is further protected from renormalization group effects in the large $\tan \beta$ limit. We calculate the $\overrightarrow{b}{\mathrm{sA}}_1^0$ amplitude at leading order in $\tan \beta$ and work out the contributions to rare K, B and radiative ${\rm Y}$ decays and $B-\overline{B}$ mixing. We obtain constraints on the $A_1^0$ mass and couplings and show that masses down to $\mathcal{O}\mathrm{}\left(10\right)\mathrm{}$ MeV are allowed. The b-physics phenomenology of the NMSSM differs from the MSSM in the appearance of sizable renormalization effects from neutral Higgs bosons to the photon and gluon dipole operators and the breakdown of the MSSM correlation between the $B_s\to {\mu }^{+}{\mu }^{-}$ branching ratio and $B_s-B_s$ mixing. For $A_1^0$ masses above the tau threshold the $A_1^0$ can be searched for in $\overrightarrow{b}s{\tau }^{+}{\tau }^{-}$ processes with branching ratios $\lesssim {10}^{-3}.$

We consider the Lorentz invariant noncommutative QED and complete the Feynman rules for the theory up to the order ${\theta }^2.$ In the Lorentz invariant version of the noncommutative QED the particles with fractional charges can be also considered. We show that in the parton model, even at the lowest order, the Bjorken scaling violates as $\sim {\theta }^2{Q}^4.$

The gluon collisional width in hot QCD plasmas is discussed with emphasis on temperatures near $T_c,$ where the coupling is large. Considering its effect on the entropy, which is known from lattice calculations, it is argued that the width, which in the perturbative limit is given by $\gamma \sim g^2\ln \mathrm{}(1/g)T,$ should be sizeable at intermediate temperatures but has to be small close to $T_c.$ Implications of these results for several phenomenologically relevant quantities, such as the energy loss of hard jets, are pointed out.

We study the polarization of hyperon in different processes in singly polarized pp collisions, in particular its relation to the polarized parton distributions. We show that by measuring hyperon polarization in particularly chosen processes, one can extract useful information on these parton distributions. We show in particular that, by measuring the ${\Sigma }^{+}$ polarization in high $p_T$ direct photon production process, one can extract information on the gluon helicity distribution; and by measuring the transverse polarization of hyperons with high $p_T$ in singly polarized reactions, one can obtain useful information on the transversity distribution. We present the numerical results obtained for those hyperon polarizations using different models for parton distribution function and those for the spin transfer in fragmentation processes.

We use soft collinear effective field theory to study nonperturbative strong interaction effects in Z decays to hadronic final states that are enhanced in corners of phase space. These occur, for example, in the jet energy distribution for two jet events near $E_J{=M}_Z/2,$ the thrust distribution near unity and the jet invariant mass distribution near zero. The extent to which such nonperturbative effects for different observables are related is discussed.

We present a measurement of the polar-angle distribution of leptons from W boson decay, as a function of the W transverse momentum. The measurement uses an $80\pm 4{\mathrm{pb}}^{-1}$ sample of $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{}\mathrm{TeV}$ collected by the CDF detector and includes data from both the $\overrightarrow{W}e+\nu$ and $\overrightarrow{W}\mu +\nu$ decay channels. We fit the W boson transverse mass distribution to a set of templates from a Monte Carlo event generator and detector simulation in several ranges of the W transverse momentum. The measurement agrees with the standard model expectation, whereby the ratio of longitudinally to transversely polarized W bosons, in the Collins-Soper W rest frame, increases with the W transverse momentum at a rate of approximately 15% per $10\mathrm{GeV}/c.\mathrm{}$