We show that the coupling of a Dirac spinor field $\psi$ with the gravitational field in the teleparallel equivalent of general relativity is consistent. For an arbitrary SO(3,1) connection ${\omega }_{\mu \mathrm{ab}}$ there are two possibilities for the coupling of $\psi$ with the gravitational field. The problems of consistency raised by Y. N. Obukhov and J. G. Pereira, Phys. Rev. D 67, 044016 (2003), occur only in the framework of one particular coupling. By adopting an alternative coupling the consistency problem disappears.

We discuss phase transitions in relativistic systems as a function of both the chemical potential and temperature. The presence of a chemical potential explicitly breaks Lorentz invariance and may additionally break other internal symmetries. This introduces new subtleties in the determination of the critical properties. We discuss separately three characteristic effects of a nonzero chemical potential. First, we consider only the explicit breaking of Lorentz invariance using a scalar field theory with a global $U\left(1\right)\mathrm{}$ symmetry. Second, we study the explicit breaking of an internal symmetry in addition to Lorentz invariance using two-color QCD at nonzero baryonic chemical potential. Finally, we consider the spontaneous breaking of a symmetry using three-color QCD at nonzero baryonic and isospin chemical potential. For each case, we derive the appropriate three-dimensional effective theory at criticality and study the effect of the chemical potential on the fixed point structure of the $\beta$ functions. We find that the order of the phase transition is not affected by the explicit breaking of Lorentz invariance but is sensitive to the breaking of additional symmetries by the chemical potential.

In this paper, we systematically study the effective action for non-commutative QED in the static limit at high temperature. When $\theta p^2\ll 1,$ where $\theta$ represents the magnitude of the parameter for non-commutativity and p denotes a typical external three-momentum, we show that this leads naturally to a derivative expansion in this model. The study of the self-energy, in this limit, leads to nontrivial $\theta$ dependent corrections to the electric and magnetic masses, which exist only above a certain critical temperature. The three point and the four point amplitudes are also studied as well as their relations to the Ward identities in this limit. We determine the closed form expression for the current involving only the spatial components of the gauge field and present the corresponding static effective action, which is gauge invariant.

The foundations are laid for the numerical computation of the actual worldline for a particle orbiting a black hole and emitting gravitational waves. The essential practicalities of this computation are illustrated here for a scalar particle of infinitesimal size and small but finite scalar charge. This particle deviates from a geodesic because it interacts with its own retarded field ${\psi }^{\mathrm{ret}}.$ A recently introduced Green’s function $G^{\mathrm{S}}$ precisely determines the singular part ${\psi }^{\mathrm{S}}$ of the retarded field. This part exerts no force on the particle. The remainder of the field ${\psi }^{\mathrm{R}}={\psi }^{\mathrm{ret}}-{\psi }^{\mathrm{S}}$ is a vacuum solution of the field equation and is entirely responsible for the self-force. A particular, locally inertial coordinate system is used to determine an expansion of ${\psi }^{\mathrm{S}}$ in the vicinity of the particle. For a particle in a circular orbit in the Schwarzschild geometry, the mode-sum decomposition of the difference between ${\psi }^{\mathrm{ret}}$ and the dominant terms in the expansion of ${\psi }^{\mathrm{S}}$ provide a mode-sum decomposition of an approximation for ${\psi }^{\mathrm{R}}$ from which the self-force is obtained. When more terms are included in the expansion, the approximation for ${\psi }^{\mathrm{R}}$ is increasingly differentiable, and the mode sum for the self-force converges more rapidly.

An algorithm based on the choice of a single monotone function (subject to boundary conditions) is presented which generates all regular static spherically symmetric perfect-fluid solutions of Einstein’s equations. For physically relevant solutions the generating functions must be restricted by nontrivial integral-differential inequalities. Nonetheless, the algorithm is demonstrated here by the construction of an infinite number of previously unknown physically interesting exact solutions.

We consider how quintessence models in which the sound speed differs from the speed of light and varies with time affect the cosmic microwave background and the fluctuation power spectrum. Significant modifications occur on length scales related to the Hubble radius during epochs in which the sound speed is near zero and the quintessence contributes a non-negligible fraction of the total energy density. For the microwave background, we find that the usual enhancement of the lowest multipole moments by the integrated Sachs-Wolfe effect can be modified, resulting in suppression or bumps instead. Also, the sound speed can produce oscillations and other effects at wave numbers $k>\mathrm{}{10}^{-2}\mathrm{h}/\mathrm{M}\mathrm{p}\mathrm{c}$ in the fluctuation power spectrum.

We show that various scalar field models of dark energy predict a degenerate luminosity distance history of the Universe and thus cannot be distinguished by supernovae measurements alone. In particular, models with a vanishing cosmological constant (the value of the potential at its minimum) are degenerate with models with a positive or negative cosmological constant whose magnitude can be as large as the critical density. Adding information from CMB anisotropy measurements does reduce the degeneracy somewhat but not significantly. Our results indicate that a theoretical prior on the preferred form of the potential and the field’s initial conditions may allow one to quantitatively estimate model parameters from the data. Without such a theoretical prior only limited qualitative information on the form and parameters of the potential can be extracted, even from very accurate data.

Realistic nonstrange hybrid compact stars with color superconducting quark matter in their interior are constructed. It is shown that a positively charged two-flavor color superconducting phase could naturally appear in the core of a hybrid star as one of the components of a globally neutral mixed phase. The negatively charged normal quark phase is the other component of the mixed phase. The quark core of the star is surrounded by another mixed phase made of hadronic and normal quark matter. The two mixed phases are separated by a sharp interface. Finally, the lowest density regions of the star are made of pure hadronic matter and a crust.

Exotic dark matter together with vacuum energy (cosmological constant) seem to dominate in a flat universe. Thus direct dark matter detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle. It is possible to obtain detectable rates, but realistically they are expected to be much lower than the present experimental goals. So one should exploit two characteristic signatures of the reaction: namely, the modulation effect and the correlation with the Sun’s motion in directional experiments. In standard nondirectional experiments the modulation is small, less than 2%. In the case of directional experiments, the main subject of this paper, we find two novel features, which are essentially independent of the supersymmetry model employed; namely, (1) the forward-backward asymmetry, with respect to the Sun’s direction of motion, is very large and (2) the modulation observed in a plane perpendicular to the Sun’s motion can be higher than 20% and is direction dependent.

The effects of space-time geometry fluctuations on fermionic fields have recently been looked for in nuclear physics experiments, and were found to be much lower than predicted, at a phenomenological level, by loop quantum gravity. We show that the possible corrections to the canonical structure in the semiclassical regime may introduce important changes in the outcome of the theory, and may explain the observed mismatch with experiments.

We present a method for the symbolic calculation of Feynman amplitudes for processes involving both massless and massive fermions. With this approach fermion strings in a specific amplitude can be easily evaluated and expressed as basic Lorentz scalars. The new approach renders the symbolic calculation of some complicated physical processes more feasible and easier, especially with the assistance of an algebra manipulating code for a computer.

The hierarchical structure of fermion masses and mixings strongly suggests an underlying family symmetry. In supergravity any familon field spontaneously breaking this symmetry necessarily acquires an F term which contributes to the soft trilinear couplings. We show that, as a result, $\overrightarrow{\mu }e\gamma$ decay can receive large contributions from this source at the level of current experimental bounds, and thus this channel may provide the first indication of supersymmetry and a clue to the structure of the soft breaking sector. Using the mercury electric dipole moment bounds, we find strong bounds on the right handed down quark mixing angles that are inconsistent with models relating them to neutrino mixing angles and favor a near-symmetric form for the magnitude of the down quark mass matrix.

A partial wave analysis (PWA) of the $\eta {\pi }^0$ system (where $\overrightarrow{\eta }\gamma \gamma )$ produced in the charge exchange reaction ${\pi }^{-}\overrightarrow{p}\eta {\pi }^{0}n$ at an incident momentum of $18\mathrm{GeV}/c$ is presented as a function of the $\eta {\pi }^0$ invariant mass $m_{\eta {\pi }^0}$ and momentum transfer squared $t_{{\pi }^{-}\to \eta \pi },$ from the incident ${\pi }^{-}$ to the outgoing $\eta {\pi }^0$ system. S, P, and D waves were included in the PWA. The $a_0\mathrm{}\left(980\right)\mathrm{}$ and $a_2\mathrm{}\left(1320\right)\mathrm{}$ states are clearly observed in the overall $\eta {\pi }^0$ effective mass distribution as well as in the amplitudes associated with S wave and D waves, respectively, after partial wave decomposition. The observed distributions in moments (averages of spherical harmonics) were compared to the results from the PWA and the two are consistent. The distribution in $t_{{\pi }^{-}\to \eta \pi }$ for individual D waves associated with natural and unnatural parity exchange in the t channel are consistent with Regge phenomenology. Of particular interest in this study is the P wave since this leads to an exotic $J^{\mathrm{PC}}{=1\mathrm{}}^{-+}$ for the $\eta \pi$ system. A P wave is present in the data; however, attempts to describe the mass dependence of the amplitude and phase motion with respect to the D wave as a Breit-Wigner resonance are problematic. This has implications regarding the existence of a reported exotic $J^{\mathrm{PC}}{=1\mathrm{}}^{-+}$ meson decaying into $\eta {\pi }^0$ with a mass near $1.4\mathrm{GeV}{/c}^2.$

We describe intersecting M5-branes, as well as M5-branes wrapping the holomorphic curve $xy=c,$ in terms of a limit of a defect conformal field theory (dCFT) with two-dimensional (4,0) supersymmetry. This defect CFT describes the low-energy theory of intersecting D3-branes at a $C^2/Z_k$ orbifold. In an appropriate $\overrightarrow{k}\infty$ limit, two compact spatial directions are generated. By identifying moduli of the M5-M5 intersection in terms of those of the defect CFT, we argue that the ${\mathrm{SU}\left(2\right)\mathrm{}}_{L}R$ symmetry of the (4,0) defect CFT matches the $\mathrm{SU}\left(2\right)\mathrm{}R$ symmetry of the $\mathcal{N}=2,d=4\mathrm{}$ theory of the M5-M5 intersection. We find a ’t Hooft anomaly in the ${\mathrm{SU}\left(2\right)\mathrm{}}_{L}R$ symmetry, suggesting that tensionless strings give rise to an anomaly in the $\mathrm{SU}\left(2\right)\mathrm{}R$ symmetry of intersecting M5-branes.

We consider a brane-induced gravity model in more than one extra dimension, regularized by assuming that the bulk gravity is soft in the ultraviolet. We study linear theory about a flat multidimensional space-time and a flat brane. We first find that this model allows for the violation of equivalence between the gravitational and inertial masses of brane matter. We then observe that the model has a scalar ghost field localized near the brane, as well as a quasilocalized massive graviton. The pure tensor structure of four-dimensional gravity on the brane at intermediate distances is due to the cancellation between the extra polarization of the massive graviton and the ghost. This is completely analogous to the situation in the GRS model.

A class of spacetimes (comprising the Alcubierre bubble, Krasnikov tube, and a certain type of wormhole) is considered that admits “superluminal travel” in a strictly defined sense. Such spacetimes (they are called “shortcuts” in this paper) were suspected to be impossible because calculations based on “quantum inequalities” suggest that their existence would involve Planck-scale energy densities and hence unphysically large values of the “total amount of negative energy” $E_{\mathrm{tot}}^{-}.$ I argue that the spacetimes of this type may not be unphysical at all. By explicit examples I prove that (1) the relevant quantum inequality does not (always) imply large energy densities, (2) large densities may not lead to large values of $E_{\mathrm{tot}}^{-},$ and (3) large $E_{\mathrm{tot}}^{-}$ being physically meaningless in some relevant situations does not necessarily exclude shortcuts.

Soft-collinear effective theory is used to prove factorization of the $\overrightarrow{B}\gamma l\nu$ decay amplitude at leading power in $\Lambda {/m}_b,$ including a demonstration of the absence of nonvalence Fock states and of the finiteness of the convolution integral in the factorization formula. Large logarithms entering the hard-scattering kernel are resummed by performing a two-step perturbative matching onto the low-energy effective theory, and by solving evolution equations derived from the renormalization properties of the leading-order B-meson light-cone distribution amplitude. As a by-product, the evolution equation for heavy-collinear current operators in soft-collinear effective theory is derived.

We study the physics potential of very long baseline neutrino-oscillation experiments with a high intensity proton accelerator which will be completed by the year 2007 in Tokai-village, as a joint project of KEK and JAERI (Japan Atomic Energy Research Institute). The 50 GeV proton synchrotron at J-PARC (Japan Proton Accelerator Research Complex) will deliver neutrino beams in the range of a few GeV with an intensity about two orders of magnitude higher than the present KEK beam for the K2K experiment. As a sequel to the proposed J-PARC–to–Super-Kamiokande experiment, we study the impact of experiments with a 100 kton-level detector and a baseline length of a few-thousand km. The pulsed narrow-band ${\nu }_{\mu }$ beams allow us to measure the ${\nu }_{\mu }\to {\nu }_e$ transition probability and the ${\nu }_{\mu }$ survival probability through counting experiments at a large water-Čerenkov detector. We study the sensitivity of such experiments to the neutrino mass hierarchy, the mass-squared differences, the three angles, and one $\mathrm{CP}$ phase of the three-generation lepton-flavor-mixing matrix. We find that experiments at a distance between 1000 and 2000 km can determine the sign of the larger mass-squared difference ${(m}_3^2-m_1^2)$ if the mixing between ${\nu }_e$ and ${\nu }_3$ (the heaviest-or-lightest neutrino) is not too small: $4|U_{e3\mathrm{}}{|}^2\left(1\mathrm{}-|U_{e3\mathrm{}}{|}^2\right)\gtrsim \mathrm{0.03.}$ The $\mathrm{CP}$ phase can be constrained if the $|U_{e3\mathrm{}}|$ element is sufficiently large: $4|U_{e3\mathrm{}}{|}^2\left(1\mathrm{}-|U_{e3\mathrm{}}{|}^2\right)\gtrsim 0.06,$ and if the smaller mass-squared difference ${(m}_2^2-m_1^2)$ and the $U_{e2\mathrm{}}$ element are in the preferred range of the large-mixing-angle solution of the solar-neutrino deficit. The magnitude $|m_3^2-m_1^2|$ and the matrix element $U_{\mu 3}$ can be precisely measured, but we find little sensitivity to $m_2^2-m_1^2$ and the matrix element $U_{e2\mathrm{}}.$

The neutral B meson lifetime is measured with the data collected by the BABAR detector at the PEP-II storage ring during the years 1999 and 2000, with a total integrated luminosity of 20.7 ${\mathrm{fb}}^{\mathrm{-}1}$. The decays $B^0\to D^{*-}{\pi }^{+}$ and $B^0\to D^{*-}{\rho }^{+}$ are selected with a partial-reconstruction technique, yielding samples of $6970\pm 240$ and $5520\pm 250$ signal events, respectively. With these events, the $B^0$ lifetime is measured to be $1.533\pm 0.034\left(\mathrm{stat}\right)\pm 0.038\left(\mathrm{syst}\right)\mathrm{ps}.$ This measurement serves as a test and validation of procedures required to measure the CP violation parameter $\sin (2\mathrm{}\beta +\gamma )$ with partial reconstruction of these modes.

The equation of state of the hypothetical dark energy component, which constitutes about two-thirds of the critical density of the Universe, may be very different from that of a cosmological constant. Employing a phenomenological model, we investigate semianalytically the constraints imposed on the scalar quintessence by supernovae observations, and by the acoustic scale extracted from recent cosmic microwave background data. We show that a universe with a quintessence-dominated phase in the dark age is consistent with the current observational constraints.