Recent work has shown that differential rotation, producing large scale drifts of fluid elements along stellar latitudes, is an unavoidable feature of $r$-modes in the nonlinear theory. We investigate the role of this differential rotation in the evolution of the $l=2$ $r$-mode instability of a newly born, hot, rapidly-rotating neutron star. It is shown that the amplitude of the $r$-mode saturates a few hundred seconds after the mode instability sets in. The saturation amplitude depends on the amount of differential rotation at the time the instability becomes active and can take values much smaller than unity. It is also shown that, independently of the saturation amplitude of the mode, the star spins down to rotation rates that are comparable to the inferred initial rotation rates of the fastest pulsars associated with supernova remnants. Finally, it is shown that, when the drift of fluid elements at the time the instability sets in is significant, most of the initial angular momentum of the star is transferred to the $r$-mode and, consequently, almost none is carried away by gravitational-radiation.

In this work, we discuss observable characteristics of the radiation emitted from a surface of a collapsing object. We study a simplified model in which a radiation of massless particles has a sharp in time profile, and it happens at the surface at the same moment of comoving time. Since the radiating surface has finite size the observed radiation will occur during some finite time. Its redshift and bending angle are affected by the strong gravitational field. We obtain a simple expression for the observed flux of the radiation as a function of time. To find an explicit expression for the flux we develop an analytical approximation for the bending angle and time delay for null rays emitted by a collapsing surface. In the case of the bending angle this approximation is an improved version of the earlier proposed Beloborodov-Leahy-approximation. For rays emitted at $R>2R_g$ the accuracy of the proposed improved approximations for the bending angle and time delay is of order (or less) than 2%–3%. By using this approximation we obtain an approximate analytical expression for the observed flux and study its properties.

In this paper we present a hybrid model of $k$-essence and chameleon, named as $k$-chameleon. In this model, due to the chameleon mechanism, the directly strong coupling between the $k$-chameleon field and matters (cold dark matters and baryons) is allowed. In the radiation-dominated epoch, the interaction between the $k$-chameleon field and background matters can be neglected; the behavior of the $k$-chameleon therefore is the same as that of the ordinary $k$-essence. After the onset of matter domination, the strong coupling between the $k$-chameleon and matters dramatically changes the result of the ordinary $k$-essence. We find that during the matter-dominated epoch, only two kinds of attractors may exist: one is the familiar $\mathbf{K}$ attractor and the other is a completely new, dubbed $\mathbf{C}$ attractor. Once the Universe is attracted into the $\mathbf{C}$ attractor, the fraction energy densities of the $k$-chameleon ${\Omega }_{\varphi }$ and dust matter ${\Omega }_m$ are fixed and comparable, and the Universe will undergo a power-law accelerated expansion. One can adjust the model so that the $\mathbf{K}$ attractor does not appear. Thus, the $k$-chameleon model provides a natural solution to the cosmological coincidence problem.

We study the implications for the minimal supersymmetric standard model (MSSM) of the absence of a direct discovery of a Higgs boson at LEP. First we exhibit 15 physically different ways in which one or more Higgs bosons lighter than the LEP limit could still exist. For each of these cases—as well as the case that the lightest Higgs eigenstate is at, or slightly above, the current LEP limit—we provide explicit sample configurations of the Higgs sector as well as the soft supersymmetry breaking Lagrangian parameters necessary to generate these outcomes. We argue that all of the cases seem fine-tuned, with the least fine-tuned outcome being that with $m_h\simeq 115\mathrm{G}\mathrm{e}\mathrm{V}$. Seeking to minimize this tuning we investigate ways in which the “maximal-mixing” scenario with large top-quark trilinear A-term can be obtained from simple string-inspired supergravity models. We find these obvious approaches lead to heavy gauginos and/or problematic low-energy phenomenology with minimal improvement in fine-tuning.

Minimal supergravity mediation of supersymmetry breaking has attracted much attention due to its simplicity, which leads to its predictive power. We consider how Nature possibly realizes minimal supergravity through inflationary selection of the theory. Minimality is impressively consistent with the present observational bounds and it might be tested with the aid of low-energy soft parameters obtained in future experiments.

Nonanalyticity of QCD with a $\theta$ term at $\theta =0$ may signal a spontaneous breaking of both parity and time reversal invariance. We address this issue by investigating the large volume limit of the topological susceptibility $\chi$ in pure SU(3) gauge theory. We obtain an upper bound for the symmetry breaking order parameter $⟨Q⟩$ and, as a by-product, the value $\chi =[173.4(\pm 0.5)(\pm 1.2){(}_{-0.2}^{+1.1})\mathrm{M}\mathrm{e}\mathrm{V}{]}^4$ at $\beta =6$ ($a\approx 0.1$ Fermi). The errors are the statistical error from our data, the one derived from the value used for ${\Lambda }_L$ and an estimate of the systematic error, respectively.

We discuss the very different roles of the valence-quark and the sea-quark residual masses ($m_{\mathrm{r}\mathrm{e}\mathrm{s}}^v$ and $m_{\mathrm{r}\mathrm{e}\mathrm{s}}^s$) in dynamical domain-wall fermions simulations. Focusing on matrix elements of the effective weak Hamiltonian containing a power divergence, we find that $m_{\mathrm{r}\mathrm{e}\mathrm{s}}^v$ can be a source of a much bigger systematic error. To keep all systematic errors due to residual masses at the 1% level, we estimate that one needs $a{m}_{\mathrm{r}\mathrm{e}\mathrm{s}}^s\lesssim {10}^{-3}$ and $a{m}_{\mathrm{r}\mathrm{e}\mathrm{s}}^v\lesssim {10}^{-5}$, at a lattice spacing $a\sim 0.1\mathrm{f}\mathrm{m}$. The practical implications are that (1) optimal use of computer resources calls for a mixed scheme with different domain-wall fermion actions for the valence and sea quarks; (2) better domain-wall fermion actions are needed for both the sea and the valence sectors.

We study the density dependence of the decay ${\pi }^0\to \gamma \gamma$ using the Skyrme Lagrangian to describe simultaneously both the matter background and mesonic fluctuations. The classical ground state configuration has different chiral properties depending on the Skyrmion density, which is reflected in the physical properties of pion fluctuating on top of the classical background. This leads to large suppression at high density of both photo-production from the neutral pion and the reverse process. The effective charges of ${\pi }^{\pm }$ are also discussed in the same framework.

The polarization of the $W$ boson in $t\to Wb$ decay is unambiguously predicted by the standard model of electroweak interactions and is a powerful test of our understanding of the $tbW$ vertex. We measure this polarization from the invariant mass of the $b$ quark from $t\to Wb$ and the lepton from $W\to l\nu$ whose momenta measure the $W$ decay angle and direction of motion, respectively. In this paper we present a measurement of the decay rate ($f_{V+A}$) of the $W$ produced from the decay of the top quark in the hypothesis of $\mathrm{V}+\mathrm{A}$ structure of the $tWb$ vertex. We find no evidence for the nonstandard $\mathrm{V}+\mathrm{A}$ vertex and set a limit on $f_{V+A}$ $<$ 0.80 at $95\%$ confidence level. By combining this result with a complementary observable in the same data, we assign a limit on $f_{V+A}$ $<$ 0.61 at $95\%$ CL. This corresponds to a constraint on the right-handed helicity component of the W polarization of $f_{+}<0.18$ at $95\%$ CL. This limit is the first significant direct constraint on $f_{V+A}$ in top decay.

A new technique is developed for the derivation of the Wess-Zumino-Witten (WZW) terms of gauged chiral Lagrangians. We start in $D=5$ with a pure (mesonless) Yang-Mills theory, which includes relevant gauge field Chern-Simons terms. The theory is then compactified, and the effective $D=4$ Lagrangian is derived using lattice techniques, or “deconstruction,” where pseudoscalar mesons arise from the lattice Wilson links. This yields the WZW term with the correct Witten coefficient by way of a simple heuristic argument. We discover a novel WZW term for singlet currents, that yields the full Goldstone-Wilczek current, and a $U(1)$ axial current for the Skyrmion, with the appropriate anomaly structures. A more detailed analysis is presented of the dimensional compactification of Yang-Mills in $D=5$ into a gauged chiral Lagrangian in $D=4$, heeding the consistency of the $D=4$ and $D=5$ Bianchi identities. These dictate a novel covariant derivative structure in the $D=4$ gauge theory, yielding a field strength modified by the addition of commutators of chiral currents. The Chern-Simons term of the pure $D=5$ Yang-Mills theory then devolves into the correct form of the Wess-Zumino-Witten term with an index (the analogue of $N_{\mathrm{c}\mathrm{o}\mathrm{l}\mathrm{o}\mathrm{r}\mathrm{s}}=3$) of $N=D=5$. The theory also has a Skyrme term with a fixed coefficient.

One considers a planar Maxwell-Chern-Simons electrodynamics in the presence of a purely spacelike Lorentz-violating background. Once the Dirac sector is properly introduced and coupled to the scalar and the gauge fields, the electron-electron interaction is evaluated as the Fourier transform of the Möller scattering amplitude (derived in the nonrelativistic limit). The associated Fourier integrations can not be exactly carried out, but the interaction potential is obtained as a first order solution in ${\mathrm{v}}^2/s^2$. It is then observed that the scalar potential presents a logarithmic attractive (repulsive) behavior near (far from) the origin. Concerning the gauge potential, it is composed of the pure MCS interaction corrected by background contributions, also responsible for its anisotropic character. It is also verified that such corrections may turn the gauge potential attractive for some parameter values. Such attractiveness remains even in the presence of the centrifugal barrier and gauge invariant $A·A$ term, which constitutes a necessary condition for yielding electron-electron pairing.

We generalize the football shaped extra dimensions scenario to an arbitrary number of branes. The problem is related to the solution of the Liouville equation with singularities, and explicit solutions are presented for the case of three branes. The tensions of the branes do not need to be tuned with each other but only satisfy mild global constraints.

The geometry around a rotating massive body, which carries charge and electrical currents, could be described by its multipole moments (mass moments, mass-current moments, electric moments, and magnetic moments). When a small body is orbiting around such a massive body, it will move on geodesics, at least for a time interval that is short with respect to the characteristic time of the binary due to gravitational radiation. By monitoring the waves emitted by the small body we are actually tracing the geometry of the central object, and hence, in principle, we can infer all its multipole moments. This paper is a generalization of previous similar results by Ryan. Ryan explored the mass and mass-current moments of a stationary, axially symmetric, and reflection symmetric, with respect to its equatorial plane, metric, by analyzing the gravitational waves emitted from a test body which is orbiting around the central body in nearly circular equatorial orbits. In our study we suppose that the gravitating source is endowed with intense electromagnetic field as well. Because of its axisymmetry the source is characterized now by four families of scalar multipole moments: its mass moments $M_l$, its mass-current moments $S_l$, its electrical moments $E_l$, and its magnetic moments $H_l$, where $l=0,1,2,\dots$. Four measurable quantities, the energy emitted by gravitational waves per logarithmic interval of frequency, the precession of the periastron, the precession of the orbital plane, and the number of cycles emitted per logarithmic interval of frequency, are presented as power series of the Newtonian orbital velocity of the test body. The power series coefficients are simple polynomials of the various moments. If any of these quantities are measured with sufficiently high accuracy, the lowest moments, including the electromagnetic ones, could be inferred and thus we could get valuable information about the internal structure of the compact massive body. The fact that the electromagnetic moments of spacetime can be measured demonstrates that one can obtain information about the electromagnetic field purely from gravitational-wave analysis. Additionally, these measurements could be used as a test of the no-hair theorem for black holes.

We derive the minimal seed magnetic field which unavoidably arises in the radiation and matter eras, prior to recombination, by the rotational velocity of ions and electrons, gravitationally induced by the nonlinear evolution of primordial density perturbations. The resulting magnetic field power spectrum is fully determined by the amplitude and spectral index of density perturbations. The rms amplitude of the seed field at recombination is $B\approx {10}^{-23}(\lambda /\mathrm{M}\mathrm{p}\mathrm{c}{)}^{-2}\mathrm{G}$, on comoving scales $\lambda \gtrsim 1\mathrm{M}\mathrm{p}\mathrm{c}$.

It is shown that a subelectronvolt upper limit can be derived on the neutrino mass from the cosmic microwave background (CMB) data alone in the $\Lambda \mathrm{C}\mathrm{D}\mathrm{M}$ model with the power-law adiabatic perturbations, without the aid of any other cosmological data. Assuming the flatness of the Universe, the constraint we can derive from the current Wilkinson Microwave Anisotropy Probe observations is $\sum _{}^{}{m}_{\nu }<2.0\mathrm{e}\mathrm{V}$ at the 95% confidence level for the sum over three species of neutrinos ($m_{\nu }<0.66\mathrm{e}\mathrm{V}$ for the degenerate neutrinos) by maximizing the likelihood over six other cosmological parameters. This constraint modifies little even if we abandon the flatness assumption for the spatial curvature. We argue that it would be difficult to improve the limit much beyond $\sum _{}^{}{m}_{\nu }\lesssim 1.5\mathrm{e}\mathrm{V}$ using only the CMB data, even if their statistics are substantially improved. However, a significant improvement of the limit is possible if an external input is introduced that constrains the Hubble constant from below. The parameter correlation and the mechanism of CMB perturbations that give rise to the limit on the neutrino mass are also elucidated.

We pursue a phenomenological study of higher-twist effects in high-energy processes by taking into account the off-shellness (virtuality) of partons bound in the nucleon. The effect of parton off-shellness in deep inelastic $ep\to eX$ scattering (DIS) and the Drell-Yan process ($pp\to l\overline{l}X$) is examined. Assuming factorization and a single-parameter Breit-Wigner form for the parton spectral function, we develop a model to calculate the corresponding off-shell cross sections. Allowing for a finite parton width $\approx 100\mathrm{M}\mathrm{e}\mathrm{V}$, we reproduce the data of both DIS and the triple-differential Drell-Yan cross section without an additional $K$-factor. The results are compared to those from perturbative QCD and the intrinsic-$k_T$ approach.

A phenomenological analysis of the distribution of Wilson loops in SU(2) Yang-Mills theory is presented in which Wilson loop distributions are described as the result of a diffusion process on the group manifold. It is shown that, in the absence of forces, diffusion implies Casimir scaling and, conversely, exact Casimir scaling implies free diffusion. Screening processes occur if diffusion takes place in a potential. The crucial distinction between screening of fundamental and adjoint loops is formulated as a symmetry property related to the center symmetry of the underlying gauge theory. The results are expressed in terms of an effective Wilson loop action and compared with various limits of SU(2) Yang-Mills theory.

We calculate the transverse momentum $p_T$ distribution for production of the ${\rm Y}$ states in hadronic reactions. For small $p_T(\le M_{{\rm Y}})$, we resum to all orders in the strong coupling ${\alpha }_s$ the process-independent large logarithmic contributions that arise from initial-state gluon showers. We demonstrate that the $p_T$ distribution at low $p_T$ is dominated by the region of small impact parameter $b$ and that it may be computed reliably in perturbation theory. We express the cross section at large $p_T$ by the $\mathcal{O}({\alpha }_s^3)$ lowest-order nonvanishing perturbative contribution. Our results are consistent with data from the Fermilab Tevatron collider.

Based on $5.8\times {10}^{7}J/\psi$ events detected in BESII, the branching fractions of $J/\psi \to \varphi \eta$ and $\varphi {\eta }^{\prime }$ are measured for different $\eta$ and ${\eta }^{\prime }$ decay modes. The results are significantly higher than previous measurements. An upper limit on $B(J/\psi \to \varphi {\pi }^0)$ is also obtained.

Deformation of $\mathcal{N}=2$ quiver gauge theories by adjoint masses leads to fixed manifolds of $\mathcal{N}=1$ superconformal field theories. We elaborate on the role of the complex three-form flux in the IIB duals to these fixed point theories, primarily using field theory techniques. We study the moduli space at a fixed point and find that it is either the two (complex) dimensional asymptotically locally Euclidean (ALE) space or three-dimensional generalized conifold, depending on the type of three-form flux that is present. We describe the exactly marginal operators that parameterize the fixed manifolds and find the operators which preserve the dimension of the moduli space. We also study deformations by arbitrary superpotentials $W({\Phi }_i)$ for the adjoints. We invoke the $a$-theorem to show that there are no dangerously irrelevant operators like $\mathrm{T}\mathrm{r}{\Phi }_i^{k+1}$, $k>2$ in the $\mathcal{N}=2$ quiver gauge theories. The moduli space of the IR fixed point theory generally contains orbifold singularities if $W({\Phi }_i)$ does not give a mass to the adjoints. Finally we examine some nonconformal $\mathcal{N}=1$ quiver theories. We find evidence that the moduli space at the endpoint of a Seiberg duality cascade is always a three-dimensional generalized conifold. In general, the low-energy theory receives quantum corrections. In several noncascading theories we find that the moduli space is a generalized conifold realized as a monodromic fibration.