This note describes a theoretical study of $Wb\overline{b}$ and $Wjj$ final states at the Tevatron using the NLO program MCFM. We extensively study the effect of NLO corrections with respect to variations of input parameters such as the minimum jet $p_T$ and the choice of renormalization and factorization scales. In particular, we examine possible implications for the Method 2 QCD background subtraction technique for $t\overline{t}$ production.

In this paper, we study generic nonlocal Nambu-Jona-Lasinio models for four-dimensional QCD in the limit of a large number of colors. We diagonalize, through a Bogoliubov-type transformation, the Hamiltonian of the model completely in terms of the compound operators creating/annihilating mesons—bound states of dressed quarks and antiquarks—and demonstrate a one-to-one correspondence between the Bogoliubov diagonalization condition and the Bethe-Salpeter equation for bound states. We conclude that, in the leading order in $N_C$, the nontrivial contents of the theory is entirely encoded in the chiral angle—the solution to the mass-gap equation for dressed quarks. As a consequence, we extend the statement of existence of excited solutions to the mass-gap equation, called vacuum replicas, beyond the BCS level and prescribe a new index to the mesonic operators—the label of the vacuum state in which the corresponding meson is created.

We present the results of a search for the radiative decay $B^0\to J/\psi \gamma$ in a data set containing $123.0\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays, collected by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ storage ring at SLAC. We find no evidence for a signal and place an upper limit of $\mathcal{B}(B^0\to J/\psi \gamma )<1.6\times {10}^{-6}$ at 90% confidence level.

We use $\epsilon$-cooling, adjusting at will the order $a^2$ corrections to the lattice action, to study the parameter space of instantons in the background of nontrivial holonomy and to determine the presence and nature of constituents with fractional topological charge at finite and zero temperature for SU(2). As an additional tool, zero-temperature configurations were generated from those at finite temperature with well-separated constituents. This is achieved by “adiabatically” adjusting the anisotropic coupling used to implement finite temperature on a symmetric lattice. The action and topological charge density, as well as the Polyakov loop and chiral zero-modes are used to analyze these configurations. We also show how cooling histories themselves can reveal the presence of constituents with fractional topological charge. We comment on the interpretation of recent fermion zero-mode studies for thermalized ensembles at small temperatures.

The effective action for wee partons in large nuclei includes a sum over static color sources distributed in a wide range of representations of the $\mathrm{S}\mathrm{U}(N_c)$ color group. The problem can be formulated as a random walk of partons in the $N_c-1$ dimensional space of the Casimir operators of $\mathrm{S}\mathrm{U}(N_c)$. For a large number of sources, $k\gg 1$, we show explicitly that the most likely representation is a classical representation of order $O(\sqrt{k})$. The quantum sum over representations is well approximated by a path integral over classical sources with an exponential weight whose argument is the quadratic Casimir operator of the group. The contributions of the higher $N_c-2$ Casimir operators are suppressed by powers of $k$. Other applications of the techniques developed here are discussed briefly.

Nonlinear realizations describing the spontaneous breakdown of supersymmetry and $R$-symmetry are constructed using the Goldstino and $R$-axion fields. The associated $R$-current, supersymmetry current and energy-momentum tensor are shown to be related under the nonlinear supersymmetry transformations. Nonlinear realizations of the superconformal algebra carried by these degrees of freedom are also displayed. The divergences of the $R$ and dilatation currents are related to the divergence of the superconformal currents through nonlinear supersymmetry transformations which in turn relates the explicit breakings of these symmetries.

A loop or coupling expansion of a so-called $n$-particle irreducible ($n\mathrm{P}\mathrm{I}$) generating functional provides a well-defined approximation scheme in terms of self-consistently dressed propagators and $n$-point vertices. A self-consistently complete description determines the functional for arbitrarily high $n$ to a given order in the expansion. We point out an equivalence hierarchy for $n\mathrm{P}\mathrm{I}$ effective actions, which allows one to obtain a self-consistently complete result in practice. The method is applied to a $\mathrm{S}\mathrm{U}(N)$ gauge theory with fermions up to four-loop or $\mathcal{O}(g^6)$ corrections. For nonequilibrium we discuss the connection to kinetic theory. The leading-order on-shell results in $g$ can be obtained from the three-loop effective action approximation, which already includes, in particular, all diagrams enhanced by the Landau-Pomeranchuk-Migdal effect. Furthermore, we compare the effective action approach with Schwinger-Dyson (SD) equations. By construction, SD equations are expressed in terms of loop diagrams including both classical and dressed vertices, which lead to ambiguities of whether classical or dressed ones should be employed at a given truncation order. We point out that these problems are absent using effective action techniques. We show that a wide class of truncations of SD equations cannot be obtained from the $n\mathrm{P}\mathrm{I}$ effective action. In turn, our results can be used to resolve SD ambiguities of whether classical or dressed vertices should be employed at a given truncation order.

We discuss the question, whether the Reissner-Nordström (RN) metric can be glued to other solutions of Einstein-Maxwell equations in such a way that (i) the singularity at $r=0$ typical of the RN metric is removed, and (ii) matching is smooth. Such a construction could be viewed as a classical model of an elementary particle balanced by its own forces without support by an external agent. One choice is the Minkowski interior that goes back to the old Vilenkin and Fomin’s idea who claimed that in this case the bare deltalike stresses at the horizon vanish if the RN metric is extremal. However, the relevant entity here is the integral of these stresses over the proper distance which is infinite in the extremal case. As a result of the competition of these two factors, the Lanczos tensor does not vanish and the extremal RN cannot be glued to the Minkowski metric smoothly, so the elementary-particle model as an empty ball inside fails. We examine the alternative possibility for the extremal RN metric—gluing to the Bertotti-Robinson (BR) metric. For a surface placed outside the horizon there always exist bare stresses but their amplitude goes to zero as the radius of the shell approaches that of the horizon. This limit realizes the Wheeler idea of ”mass without mass” and ”charge without charge.” We generalize the model to the extremal Kerr-Newman metric glued to the rotating analog of the BR metric.

We define and extensively test a set of boundary conditions that can be applied at black-hole excision surfaces when the Hamiltonian and momentum constraints of general relativity are solved within the conformal thin-sandwich formalism. These boundary conditions have been designed to result in black holes that are in quasiequilibrium and are completely general in the sense that they can be applied with any conformal three-geometry and slicing condition. Furthermore, we show that they retain precisely the freedom to specify an arbitrary spin on each black hole. Interestingly, we have been unable to find a boundary condition on the lapse that can be derived from a quasiequilibrium condition. Rather, we find evidence that the lapse boundary condition is part of the initial temporal gauge choice. To test these boundary conditions, we have extensively explored the case of a single black hole and the case of a binary system of equal-mass black holes, including the computation of quasicircular orbits and the determination of the innermost stable circular orbit. Our tests show that the boundary conditions work well.

We discuss the quantum states in the moduli space, which are constructed with maximally charged dilaton black holes. Considering the quantum mechanics in the moduli space, we obtain the asymptotic states for the near-coincident black holes and the widely separated black holes. We study the scattering process of the dilaton black holes with the asymptotic states. In the scattering process, the quantum effects in the black hole moduli space are investigated.

Dark matter annihilations can generate significant amounts of internal heat inside planets if dark matter consists mainly of particles with nuclear cross sections in the microbarn range or larger (SIMPs). By considering a detailed model of Uranus's interior, we calculate upper limits on the S-wave annihilation cross section for these particles as a function of their mass. These upper limits, together with other experimental and theoretical constraints, rule out SIMPs with masses between 150 MeV and ${10}^4\mathrm{G}\mathrm{e}\mathrm{V}$.

We argue that a brane-world with a warped, infinite extra dimension allows for the inflaton to decay into the bulk so that after inflation, the effective dark energy disappears from our brane. This is achieved by shifting away the decay products into the infinity of the 5th dimension. As a consequence, all matter and CMB density perturbations could have their origin in the decay of a MSSM flat direction rather than the inflaton. We also discuss a string theoretical model where reheating after inflation may not affect the observable brane.

We study the SU(3) group structure of pentaquark baryons which are made of four quarks and one antiquark. The pentaquark baryons form $\mathbf{1}$, $\mathbf{8}$, $\mathbf{10}$, $\overline{\mathbf{10}}$, $\mathbf{27}$, and $\mathbf{35}$ multiplets in the SU(3) quark model. First, the flavor wave functions of all the pentaquark baryons are constructed in the SU(3) quark model and then the flavor SU(3) symmetry relations for the interactions of the pentaquarks with three-quark baryons and pentaquark baryons are obtained. Constructing the general interactions in SU(3) could be important for understanding the pentaquark baryon properties from reaction mechanisms. We also discuss possible pentaquarks in $\mathbf{27}$-plet and $\mathbf{35}$-plet and their decay channels that can be used to identify them in future experiments. The mass sum rules for the pentaquark baryons are also presented.

Parton-parton collisions do not neutralize local color charges in the quark-gluon plasma as they only redistribute the charges among momentum modes. We discuss color diffusion and color conductivity as the processes responsible for the neutralization of the plasma. For this purpose, we first compute the conductivity and diffusion coefficients in the plasma that is significantly colorful. Then, the time evolution of the color density due to the conductivity and diffusion is studied. The conductivity is shown to be much more efficient than the diffusion in neutralizing the plasma at the scale longer than the screening length. Estimates of the characteristic time scales, which are based on close to global equilibrium computations, suggest that first the plasma becomes white and then the momentum degrees of freedom thermalize.

We study the discovery potential of the Tevatron for a $Z^{\prime }$ gauge boson. We introduce a parametrization of the $Z^{\prime }$ signal which provides a convenient bridge between collider searches and specific $Z^{\prime }$ models. The cross section for $p\overline{p}\to Z^{\prime }X\to {\ell }^{+}{\ell }^{-}X$ depends primarily on the $Z^{\prime }$ mass and the $Z^{\prime }$ decay branching fraction into leptons times the average square coupling to up and down quarks. If the quark and lepton masses are generated as in the standard model, then the $Z^{\prime }$ bosons accessible at the Tevatron must couple to fermions proportionally to a linear combination of baryon and lepton numbers in order to avoid the limits on $Z-Z^{\prime }$ mixing. More generally, we present several families of U(1) extensions of the standard model that include as special cases many of the $Z^{\prime }$ models discussed in the literature. Typically, the CDF and D0 experiments are expected to probe $Z^{\prime }$-fermion couplings down to 0.1 for $Z^{\prime }$ masses in the 500–800 GeV range, which in various models would substantially improve the limits set by the LEP experiments.

We derive double distributions for the proton in a simple model that contains scalar as well as axial-vector diquark correlations. The model parameters are tuned so that the experimentally measured electromagnetic form factors of the proton are reproduced for small momentum transfer. Resulting generalized parton distributions satisfy known constraints, including the positivity bounds.

We present a new measurement of atmospheric muons made during an ascent of the High Energy Antimatter Telescope balloon experiment. The muon charge ratio ${\mu }^{+}/{\mu }^{-}$ as a function of atmospheric depth in the momentum interval 0.3–0.9 GeV/c is presented. The differential ${\mu }^{-}$ intensities in the 0.3–50 GeV/c range and for atmospheric depths between $4–960\mathrm{g}/{\mathrm{c}\mathrm{m}}^2$ are also presented. We compare these results with other measurements and model predictions. We find that our charge ratio is $\sim 1.1$ for all atmospheric depths and is consistent, within errors, with other measurements and the model predictions. We find that our measured ${\mu }^{-}$ intensities are also consistent with other measurements, and with the model predictions, except at shallow atmospheric depths.

We point out that in decays of the type $B^{-}\to D^{*}{K}^{-}$, where the neutral $D^{*}$ meson is an admixture of $D^{*0}$ and ${\overline{D}}^{*0}$, there is an effective strong phase difference of $\pi$ between the cases that the $D^{*}$ is reconstructed as $D{\pi }^0$ and $D\gamma$. We consider the consequences for measurements of ${\varphi }_3$ using these modes, some of which are profound and beneficial.

We develop the moduli-space approximation for the low energy regime of Bogomolnyi-Prasad-Sommerfield (BPS) branes with a bulk scalar field to obtain an effective four-dimensional action describing the system. An arbitrary BPS potential is used and account is taken of the presence of matter in the branes and small supersymmetry breaking terms. The resulting effective theory is a bi-scalar tensor theory of gravity. In this theory, the scalar degrees of freedom can be stabilized naturally without the introduction of additional mechanisms other than the appropriate BPS potential. We place observational constraints on the shape of the potential and the global configuration of branes.

Fermion-antifermion pair production in the presence of classical fields is described based on the retarded and advanced fermion propagators. They are obtained by solving the equation of motion for the Dirac Green's functions with the respective boundary conditions to all orders in the field. Subsequently, various approximation schemes fit for different field configurations are explained. This includes longitudinally boost-invariant forms. Those occur frequently in the description of ultrarelativistic heavy-ion collisions in the semiclassical limit. As a next step, the gauge invariance of the expression for the expectation value of the number of produced fermion-antifermion pairs as a functional of said propagators is investigated in detail. Finally, the calculations are carried out for a longitudinally boost-invariant model field, especially taking care of the last issue.