We consider the phenomenological implications of a soft supersymmetry (SUSY) breaking term $\tilde{B}N$ at the TeV scale [here $\tilde{B}$ is the $\mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_Y$ gaugino and N is the right-handed neutrino field]. In models with a massless (or nearly massless) neutralino, such a term will give rise through the seesaw mechanism to new contributions to the mass matrix of the light neutrinos. We treat the massless neutralino as an (almost) sterile neutrino and find that its mass depends on the square of the soft SUSY breaking scale, with interesting consequences for neutrino physics. We also show that, although it requires finetuning, a massless neutralino in the minimal supersymmetric standard model or next-to-minimal supersymmetric standard model is not experimentally excluded. The implications of this scenario for neutrino physics are discussed.

Higgs-boson production in association with W or Z bosons, $p\overline{p}\to WH/ZH+X,$ is the most promising discovery channel for a light standard model Higgs particle at the Fermilab Tevatron. We present the calculation of the electroweak $O\left(\alpha \right)$ corrections to these processes. The corrections decrease the theoretical prediction by up to 5%–10%, depending in detail on the Higgs-boson mass and the input-parameter scheme. We update the cross-section prediction for associated WH and ZH production at the Tevatron and at the CERN LHC, including the next-to-leading order electroweak and QCD corrections, and study the theoretical uncertainties induced by factorization and renormalization scale dependences and by the parton distribution functions.

We apply the quartic exponential variational approximation to the symmetry breaking phenomena of a scalar field in three and four dimensions. We calculate the effective potential and effective action for the time-dependent system by separating the zero mode from other nonzero modes of the scalar field and treating the zero mode quantum mechanically. It is shown that the quantum mechanical properties of the zero mode play a nontrivial role in the symmetry breaking of the scalar $\lambda {\phi }^4$ theory.

Using the well-known “displace, cut, and reflect” method used to generate disks from given solutions of Einstein’s field equations, we construct static disks made of a perfect fluid based on vacuum Schwarzschild’s solution in isotropic coordinates. The same method is applied to different exact solutions to Einstein’s equations that represent static spheres of perfect fluids. We construct several models of disks with axially symmetric perfect fluid halos. All disks have some common features: surface energy density and pressure decrease monotonically and rapidly with the radius. As the “cut” parameter a decreases, the disks become more relativistic, with the surface energy density and pressure more concentrated near the center. Also, regions of unstable circular orbits are more likely to appear for high relativistic disks. Parameters can be chosen so that the sound velocity in the fluid and the tangential velocity of test particles in circular motion are less than the velocity of light. This tangential velocity first increases with radius and reaches a maximum.

We emphasize that charged slepton pairs produced via vector-boson fusion along with two high-mass, high-$p_T$ forward and backward jets (in two opposite hemispheres) can have a higher production cross section for heavy slepton masses than that from conventional Drell-Yan production at a hadronic collider such as the CERN LHC. We analyze the signal and leading backgrounds in detail in the minimal supersymmetric standard model with conserved baryon and lepton numbers. Our investigation reveals that the mass reach of the vector-boson fusion channel is certainly an improvement over the scope of the Drell-Yan mode.

Slow-moving $(v\sim 15\mathrm{k}\mathrm{m}/\mathrm{s})$ “dark matter particles” have allegedly been discovered in a recent experiment. We explore the possibility that these slow moving dark matter particles are small mirror matter dust particles originating from our solar system. Ways of further testing our hypothesis, including the possibility of observing these dust particles in cryogenic detectors such as NAUTILUS, are also discussed.

We evaluate the noncommutative Chern-Simons action induced by fermions interacting with an Abelian gauge field in a noncommutative massive Thirring model in (2+1)-dimensional spacetime. This calculation is performed in the Dirac and Majorana representations. We observe that in the Majorana representation when $\overline{\theta }$ goes to zero we do not have an induced Chern-Simons term in the dimensional regularization scheme.

We derive, in noncommutative QED, a gauge covariant quantum equation of motion for the photon Wigner operator. In the classical approximation, this reduces to a simple transport equation which describes the hard thermal effects in this theory. As an example of the effectiveness of this method we show that, to leading order, this equation generates in a direct way the Green amplitudes calculated perturbatively in quantum field theory at high temperature.

In this paper we consider the stability of some inflating brane-world models in quantum cosmology. It is shown that, whereas the singular model based on the construction of inflating branes from Euclidean five-dimensional anti–de Sitter space is unstable to tensorial cosmological perturbations in the bulk, the nonsingular model which uses a five-dimensional asymptotically anti–de Sitter wormhole to construct the inflating branes is stable to these perturbations.

Lüscher’s “admissibility” condition on the gauge field space plays an essential role in constructing lattice gauge theories which have exact chiral symmetries. We apply the gauge action proposed by Lüscher with the domain-wall fermion action to the numerical simulation of the massive Schwinger model. We find this action can generate configurations in each topological sector separately without any topology changes. By developing a new method to sum over different topological sectors, we calculate the meson masses in the nonzero $\theta$ vacuum.

We calculate the masses of the lowest lying eigenstates of improved SU(2), SU(3), SU(4) and SU(5) Hamiltonian lattice gauge theory in 2+1 dimensions using an analytic variational approach. The ground state is approximated by a one plaquette trial state and mass gaps are calculated in the symmetric and antisymmetric sectors by minimizing over a suitable basis of rectangular states. Analytic techniques are developed to handle the group integrals arising in the calculation.

We calculate the mass spectra and decay widths of glueballs in the flux tube model. The glueball is assumed to be a flux tube ring. The breathing and the rotational motions are investigated using the WKB approximation. The calculated spectrum is consistent with those obtained by lattice QCD. The decay widths are also computed using the Schwinger mechanism, and it is shown that they have rather large values.

We show that the amplitudes for B decays into two light mesons at leading order in soft-collinear effective theory are factorized to all orders in ${\alpha }_s.$ We construct gauge-invariant four-quark operators by employing the effective theories ${\mathrm{SCET}}_{\mathrm{I}}$ for $\sqrt{m_b\Lambda }<\mu <m_b,$ and ${\mathrm{SCET}}_{\mathrm{II}}$ for $\mu <\sqrt{m_b\Lambda }$ with $\Lambda \sim 0.5$ GeV. These operators do not allow gluon exchanges between different sectors of the current and the matrix elements are reduced to the products of current matrix elements. The spectator interactions are also factorized at leading order in SCET and to all orders in ${\alpha }_s.$

We argue that the Penrose limit of a general string background is a generalization of the Seiberg-Sen limit describing M(atrix) theory as the discrete light cone quantization (DLCQ) of M theory in flat space. The Berenstein-Maldacena-Nastase (BMN) theory of type IIB strings on the maximally supersymmetric pp-wave background is understood as the exact analogue of the Banks-Fischler-Shenker-Susskind M(atrix) theory, namely, a DLCQ of type IIB string theory on ${\mathrm{AdS}}_5\times {\mathrm{S}}^5$ in the limit of infinite longitudinal momentum. This point of view is used to explain some features of the BMN duality.

We show that the lowest nontrivial truncation of the two-particle irreducible (2PI) effective action correctly determines transport coefficients in a weak coupling or $1/N$ expansion at leading (logarithmic) order in several relativistic field theories. In particular, we consider a single real scalar field with cubic and quartic interactions in the loop expansion, the $O\left(N\right)\mathrm{}$ model in the 2PI-$1/N$ expansion, and QED with single and many fermion fields. Therefore, these truncations will provide a correct description, to leading (logarithmic) order, of the long time behavior of these systems, i.e. the approach to equilibrium. This supports the promising results obtained for the dynamics of quantum fields out of equilibrium using 2PI effective action techniques.

We study the propagation of pions at finite temperature and finite chemical potential in the framework of the linear sigma model with 2 quark flavors and $N_c$ colors. The velocity of massless pions in general differs from that of light. One-loop calculations show that in the chiral symmetry broken phase pions, under certain conditions, propagate faster than light.

In this paper, we derive from the viewpoint of the effective 4D theory the interaction terms between linearized gravity propagating in $N>~2$ large extra dimensions and matter propagating into one extra dimension. This generalizes known results for the interactions between gravity and 4D matter in Arkani-Hamed–Dimopoulos–Dvali–type models. Although we assume that matter is described by a universal extra dimension (UED) scenario (with all fields propagating into the fifth dimension), we present our results in a general form that can be easily adapted to various other scenarios of matter distribution. We then apply our results to the UED model on a fat brane and consider some phenomenological applications. Among these are the computation of the gravitational decay widths of the matter Kaluza-Klein (KK) excitations and the effect the width of the brane has on the interactions of gravity with standard model particles. We also estimate the cross section for producing single KK excitations at colliders through KK number-violating gravitational interaction.

The collision of pure electromagnetic plane waves with collinear polarization in N-dimensional $\mathrm{}(N=2+n)\mathrm{}$ Einstein-Maxwell theory is considered. A class of exact solutions for the higher dimensional Bell-Szekeres metric is obtained and its singularity structure is examined.

The full sky cosmic microwave background polarization field can be decomposed into “electric” (E) and “magnetic” (B) components that are signatures of distinct physical processes. We give a general construction that achieves separation of E and B modes on arbitrary sections of the sky at the expense of increasing the noise. When E modes are present on all scales the separation of all of the B signal is no longer possible: there are inevitably ambiguous modes that cannot be separated. We discuss the practicality of performing $E/B$ decomposition on large scales with realistic nonsymmetric sky cuts, and show that separation on large scales is possible by retaining only the well supported modes. The large scale modes potentially contain a great deal of useful information, and $E/B$ separation at the level of the map is essential for clean detection of B without confusion from cosmic variance due to the E signal. We give simple matrix manipulations for creating pure E and B maps of the large scale signal for general sky cuts. We demonstrate that the method works well in a realistic case and give estimates of the performance with data from the Planck satellite. In the Appendix we discuss the simple analytic case of an azimuthally symmetric cut, and show that exact $E/B$ separation is possible on an azimuthally symmetric cut with a finite number of nonintersecting circular cuts around foreground sources.