The high accuracy envisaged for future measurements of $W$-boson production at hadron colliders has to be matched by precise theoretical predictions. We study the impact of electroweak radiative corrections on $W$-boson production cross sections and differential distributions at the Tevatron and at the LHC. In particular, we include photon-induced processes, which contribute at $\mathcal{O}(\alpha )$, and leading radiative corrections beyond $\mathcal{O}(\alpha )$ in the high-energy Sudakov regime and from multiphoton final-state radiation. We furthermore present the calculation of the complete supersymmetric next-to-leading-order electroweak and QCD corrections to $W$-boson hadroproduction within the minimal supersymmetric standard model. The supersymmetric corrections turn out to be negligible in the vicinity of the $W$ resonance in general, reaching the percent level only at high lepton transverse momentum and for specific choices of the supersymmetric parameters.

We discuss the effect of the recent change of $V_{us}$ by 3 standard deviations on the standard model predictions for neutron beta decay observables. We also discuss the effect the experimental error bars of $V_{us}$ have on such predictions. Refined precision tests of the standard model will be made by a combined effort to improve measurements in neutron beta decay and in strangeness-changing decays. By itself the former will yield very precise measurements of $V_{ud}$ and also make very precise predictions for $V_{us}$.

We suggest a perturbative approach for generic choices for the universe equation of state and introduce a novel framework for studying mass varying neutrinos (MaVaN’s) coupled to the dark sector. For concreteness, we examine the coupling between neutrinos and the underlying scalar field associated with the generalized Chaplygin gas (GCG), a unification model for dark energy and dark matter. It is shown that the application of a perturbative approach to MaVaN mechanisms translates into a constraint on the coefficient of a linear perturbation, which depends on the ratio between a neutrino energy dependent term and scalar field potential terms. We quantify the effects on the MaVaN sector by considering neutrino masses generated by the seesaw mechanism. After setting the GCG parameters in agreement with general cosmological constraints, we find that the squared speed of sound in the neutrino-scalar GCG fluid is naturally positive. In this scenario, the model stability depends on previously set up parameters associated with the equation of state of the universe. Our results suggest that the GCG is a particularly suitable candidate for constructing a stable MaVaN scenario.

The influence of dark matter inhomogeneities on the angular size-redshift test is investigated for a large class of flat cosmological models driven by dark energy plus a cold dark matter component (XCDM). The results are presented in two steps. First, the mass inhomogeneities are modeled by a generalized Zeldovich-Kantowski-Dyer-Roeder distance which is characterized by a smoothness parameter $\alpha (z)$ and a power index $\gamma$, and, second, we provide a statistical analysis to angular size data for a large sample of milliarcsecond compact radio sources. As a general result, we have found that the $\alpha$ parameter is totally unconstrained by this sample of angular-diameter data.

The cosmological constant $\Lambda$, i.e., the energy density stored in the true vacuum state of all existing fields in the Universe, is the simplest and the most natural possibility to describe the current cosmic acceleration. However, despite its observational successes, such a possibility exacerbates the well-known $\Lambda$ problem, requiring a natural explanation for its small, but nonzero, value. In this paper we study cosmological consequences of a scenario driven by a varying cosmological term, in which the vacuum energy density decays linearly with the Hubble parameter, $\Lambda \propto H$. We test the viability of this scenario and study a possible way to distinguish it from the current standard cosmological model by using recent observations of type Ia supernova (Supernova Legacy Survey Collaboration), measurements of the baryonic acoustic oscillation from the Sloan Digital Sky Survey, and the position of the first peak of the cosmic microwave background angular spectrum from the three-year Wilkinson Microwave Anisotropy Probe.

A new mechanism of adjustment of vacuum energy down to the observed value from an initially huge one is considered. The mechanism is based on a very strong variation of the gravitational coupling constant in the very early universe. The model predicts that the noncompensated remnant of vacuum energy changes very slowly at late stages of the cosmological evolution and is naturally close to the observed one. Asymptotically the effective vacuum energy tends to a negative value, so the cosmological expansion should stop and turn into contraction. There remains the problem of introduction of the usual matter into the model and therefore realizing realistic cosmology.

We study an $SU(2)$ supersymmetric gauge model in a framework of gauge-Higgs unification. Multi-Higgs spectrum appears in the model at low energy. We develop a useful perturbative approximation scheme for evaluating effective potential to study the multi-Higgs mass spectrum. We find that both tree-massless and massive Higgs scalars obtain mass corrections of similar size from finite parts of the loop effects. The corrections modify the multi-Higgs mass spectrum, and hence, the loop effects are significant in view of future verifications of the gauge-Higgs unification scenario in high-energy experiments.

We consider an effective field theory for the nonleptonic decay in which a heavy quark decays into a pair of a heavy quark and antiquark having a small relative velocity and one relativistic (massless) quark. This effective theory is a combination of heavy quark effective theory (HQET), soft-collinear effective theory (SCET), and a covariant modification of nonrelativistic QCD (NRQCD). In the leading logarithm approximation the effective theory decay amplitude factorizes into the product of matrix elements of heavy-to-heavy and heavy-to-light currents. We discuss a possibility of factorization beyond the leading logarithm approximation and find it doubtful. The Wilson coefficients of the effective theory electroweak (EWET) Lagrangian in the next-to-leading logarithm approximation are calculated at the matching scale of the decay. The differential decay rate for the inclusive decay $B\to J/\psi +h$ in the effective theory framework is evaluated.

Let us denote by $p(\mathbf{x}|\mathbf{K})$ the space density of the points where identical particles of some kind, e.g. ${\pi }^{+}$ mesons, with momentum $\mathbf{K}$ are produced. When using the HBT method to determine $p(\mathbf{x}|\mathbf{K})$ one encounters ambiguities. We show that these ambiguities do not affect the even cumulants of the distribution $p(\mathbf{x}|\mathbf{K})$. In particular, the HBT radii of the homogeneity regions, which are given by the second order cumulants, and the distribution of distances between the pairs of production points for particles with momentum $\mathbf{K}$ can be reliably measured. The odd cumulants are ambiguous. They are, however, correlated. In particular, when the average position $⟨\mathbf{x}⟩(\mathbf{K})$ is known as a function of $\mathbf{K}$ there is no further ambiguity.

We study the discrepancy between the analytical definition and the numerical implementation of the McLerran-Venugopalan model. The infinitesimal extent of a fast-moving nucleus should retain longitudinal randomness in the color source distribution even when the longitudinal extent approximates zero due to the Lorentz contraction, which is properly taken into account in the analytical treatment. We point out that the longitudinal randomness is lost in numerical simulations because of the lack of the path-ordering of the Wilson line along the longitudinal direction. We quantitatively investigate how much the results with and without longitudinal randomness differ from each other. We finally mention that the discrepancy could be absorbed in a choice of the model parameter in the physical unit, and, nevertheless, it should be an important problem in the McLerran-Venugopalan model as a fully theoretical approach.

Correlations in the properties of the static compact stars (CSs) and the ones rotating with the highest observed frequency of 1122 Hz are studied using a large set of equations of state (EOSs). These EOSs span various approaches and their chemical composition varies from the nucleons to hyperons and quarks in $\beta$-equilibrium. It is found that the properties of static CS, like the maximum gravitational mass $M_{\max }^{\mathrm{stat}}$ and radius $R_{1.4}^{\mathrm{stat}}$ corresponding to the canonical mass and supramassive or nonsupramassive nature of the CS rotating at 1122 Hz are strongly correlated. In particular, only those EOSs yield the CS rotating at 1122 Hz to be nonsupramassive for which $(\frac{M_{\max }^{\mathrm{stat}}}{M_{\odot }}{)}^{1/2}(\frac{10\mathrm{km}}{R_{1.4}^{\mathrm{stat}}}{)}^{3/2}$ is greater than unity. A suitable parametric form which can be used to split the $M_{\max }^{\mathrm{stat}}–R_{1.4}^{\mathrm{stat}}$ plane into the regions of different supramassive nature of the CS rotating at 1122 Hz is presented. Currently measured maximum gravitational mass $1.76M_{\odot }$ of PSR J0437-4715 suggests that the CS rotating at 1122 Hz can be nonsupramassive provided $R_{1.4}^{\mathrm{stat}}\le 12.4\mathrm{km}$.

In the Hamiltonian approach to Coulomb gauge Yang-Mills theory, the functional Schrödinger equation is solved variationally resulting in a set of coupled Dyson-Schwinger equations. These equations are solved self-consistently in the subcritical regime defined by infrared-finite form factors. It is shown that the Dyson-Schwinger equation for the Coulomb form factor fails to have a solution in the critical regime where all form factors have infrared divergent power laws.

The explicit one-loop renormalizability of the gluon sector of QCD with Lorentz violation is demonstrated. The result is consistent with multiplicative renormalization, as the required counterterms are consistent with a single rescaling of the Lorentz-violation parameters. In addition, the resulting beta functions indicate that the CPT-even Lorentz-violating terms increase with energy scale in opposition to the asymptotically free gauge coupling and CPT-odd terms. The calculations are performed at lowest order in the Lorentz-violating terms, as they are assumed small.

We propose an approach for the calculation of self-forces, energy fluxes and waveforms arising from moving point charges in curved spacetimes. As opposed to mode-sum schemes that regularize the self-force derived from the singular retarded field, this approach regularizes the retarded field itself. The singular part of the retarded field is first analytically identified and removed, yielding a finite, differentiable remainder from which the self-force is easily calculated. This regular remainder solves a wave equation which enjoys the benefit of having a nonsingular source. Solving this wave equation for the remainder completely avoids the calculation of the singular retarded field along with the attendant difficulties associated with numerically modeling a delta-function source. From this differentiable remainder one may compute the self-force, the energy flux, and also a waveform which reflects the effects of the self-force. As a test of principle, we implement this method using a 4th-order ($1+1$) code, and calculate the self-force for the simple case of a scalar charge moving in a circular orbit around a Schwarzschild black hole. We achieve agreement with frequency-domain results to $\sim 0.1\%$ or better.

With the assumption that the $X(1835)$ and $\eta (1760)$ recently observed by the BES Collaboration are the $3{}^{1}S_0$ meson states, the strong decays of these two states are investigated in the ${}^{3}P_0$ decay model. We find that the predicted total widths of the $X(1835)$ and $\eta (1760)$ can be reasonably reproduced with the $X(18350)-\eta (1760)$ mixing angle lying on the range from $-0.26$ to $+0.55$ radians. Further, the mixing angle of the $X(1835)$ and $\eta (1760)$ is phenomenologically determined to be about $-0.24$ radians in the presence of the $\pi (1800)$, $K(1830)$, $\eta (1760)$, and $X(1835)$ belonging to the $3{}^{1}S_0$ meson nonet. Our estimated mixing angle can naturally account for the widths of the $X(1835)$ and $\eta (1760)$, which shows that the assignment of the $X(1835)$ and $\eta (1760)$, together the $\pi (1800)$ and $K(1830)$ as the $3{}^{1}S_0$ $q\overline{q}$ members, seems reasonable.

We present a calculation of interference effects in $Hjj$ production via gluon fusion and via vector boson fusion, respectively, beyond tree level. We reproduce results recently discussed in the literature, but go beyond this calculation by including a class of diagrams not considered previously. Special care is taken in developing a numerically stable and flexible parton-level Monte Carlo program which allows us to study cross sections and kinematic distributions within experimentally relevant selection cuts. Loop-induced interference contributions are found to exhibit kinematical distributions different in shape from vector boson fusion. Because of the small interference cross section and cancellation among different quark flavor contributions, their impact on the signal process is found to be negligible in all regions of phase space, however.

Supposing only Lorentz and the gauge invariances of the Lagrangian, we derive energy and angular distributions for ${\tau }^{\pm }\to {\mu }^{\pm }{\mu }^{\pm }{\mu }^{\mp }$ lepton flavor violating decay process. Using these results, we discuss methods to determine the parameters associated with the lepton flavor violating interactions.

We examine a recently proposed symmetry/condition by Friedberg and Lee in a framework where three right-handed neutrinos are added to the spectrum of the three-family minimal standard model. It is found that the right-handed neutrinos are very special, with respect to this symmetry. In the symmetry limit the neutrinos are massless, which could possibly be a hint about why they are light. Imposed as a condition and not as a full symmetry, we find that one of the three right-handed neutrinos simply decouples (has only gravitational interactions) and one of the interacting neutrinos is massless. The possible relation of the model to the seesaw mechanism is briefly discussed.

Using holographic QCD based on D4-branes and D8-anti-D8-branes, we have computed couplings of glueballs to light mesons. We describe glueball decay by explicitly calculating its decay widths and branching ratios. Interestingly, while glueballs remain less well understood both theoretically and experimentally, our results are found to be consistent with the experimental data for the scalar glueball candidate $f_0(1500)$. More generally, holographic QCD predicts that decay of any glueball to $4{\pi }^0$ is suppressed, and that mixing of the lightest glueball with $q\overline{q}$ mesons is small.