We study cosmological solutions to the low-energy effective action of heterotic string theory including possible leading order ${\alpha }^{\prime }$ corrections and a potential for the dilaton. We consider the possibility that including such stringy corrections can resolve the initial cosmological singularity. Since the exact form of these corrections is not known the higher-derivative terms are constructed so that they vanish when the metric is de Sitter spacetime. The constructed terms are compatible with known restrictions from scattering amplitude and string worldsheet beta-function calculations. Analytic and numerical techniques are used to construct a singularity-free cosmological solution. At late times and low-curvatures the metric is asymptotically Minkowski and the dilaton is frozen. In the high-curvature regime the universe enters a de Sitter phase.

Cosmological variation of the fine structure constant $\alpha$ due to the evolution of a spatially homogeneous ultralight scalar field $\left(m\sim H_0\right)$ during the matter and $\Lambda$ dominated eras is analyzed. Agreement of $\Delta \alpha /\alpha$ with the value suggested by recent observations of quasar absorption lines is obtained by adjusting a single parameter, the coupling of the scalar field to matter. Asymptotically $\alpha \mathrm{}\left(t\right)\mathrm{}$ in this model goes to a constant value $\overline{\alpha }\approx {\alpha }_0$ in the early radiation and the late $\Lambda$ dominated eras. The coupling of the scalar field to (nonrelativistic) matter drives $\alpha$ slightly away from $\overline{\alpha }$ in the epochs when the density of matter is important. Simultaneous agreement with the more restrictive bounds on the variation $|\Delta \alpha /\alpha |$ from the Oklo natural fission reactor and from meteorite samples can be achieved if the mass of the scalar field is on the order of 0.5–0.6 $H_{\Lambda },$ where $H_{\Lambda }={\Omega }_{\Lambda }^{1/2}{H}_0.$ Depending on the scalar field mass, $\alpha$ may be slightly smaller or larger than ${\alpha }_0$ at the times of big bang nucleosynthesis, the emission of the cosmic microwave background, the formation of early solar system meteorites, and the Oklo reactor. The effects on the evolution of $\alpha$ due to nonzero mass for the scalar field are emphasized. An order of magnitude improvement in the laboratory technique could lead to a detection of $(\dot{\alpha }/\alpha {)}_0.$

We consider the spectroscopy of heavy-quark light-quark mesons with a simple model based on the nonrelativistic reduction of vector and scalar exchange between fermions. Four forces are induced: the spin-orbit forces on the light and heavy quark spins, the tensor force, and a spin-spin force. If the vector force is Coulombic, the spin-spin force is a contact interaction, and the tensor force and spin-orbit force on the heavy quark to order ${1/m}_1{m}_2$ are directly proportional. As a result, just two independent parameters characterize these perturbations. The measurement of the masses of three p-wave states suffices to predict the mass of the fourth. This technique is applied to the $D_s$ system, where the newly discovered state at 2.32 GeV provides the third measured level, and to the D system. The mixing of the two $J^P{=1\mathrm{}}^{+}$ p-wave states is reflected in their widths and provides additional constraints. The resulting picture is at odds with previous expectations and raises new puzzles.

We evaluate the ratio of the scale parameter $\Lambda$ in domain wall QCD to the one in continuum theory at the one-loop level incorporating the effect of massless quarks. We show that the Pauli-Villars regulator is required to subtract the unphysical massive fermion modes that emerge in the fermion loop contributions to the gluon self-energy. Detailed results are presented as a function of the domain wall height M.

We derive the minimal Fock-state expansion of the pion and the photon wave functions in the light-cone formalism; then we calculate the pion-photon and the photon-pion transition form factors of the ${\gamma }^{*}{\pi }^0\to \gamma$ and ${\gamma }^{*}\overrightarrow{\gamma }{\pi }^0$ processes by employing these quark-antiquark wave functions of the pion and the photon. We find that our calculation for the ${\gamma }^{*}\overrightarrow{\gamma }{\pi }^0$ transition form factor agrees with the experimental data at low and moderately high energy scales. Moreover, the physical differences and inherent connections between the transition form factors of ${\gamma }^{*}{\pi }^0\to \gamma$ and ${\gamma }^{*}\overrightarrow{\gamma }{\pi }^0$ have been illustrated, indicating that these two physical processes are intrinsically related. In addition, we discuss the ${\pi }^0\to \gamma \gamma$ form factor and the decay width $\mathit{\Gamma }\left(\overrightarrow{\pi }\gamma \gamma \right)$ at $Q^2=0.\mathrm{}$

The masses of the p-wave excited heavy baryons have been calculated to ${\Lambda }_{\mathrm{QCD}}{/m}_Q$ order using the QCD sum rule method within the framework of heavy quark effective theory. Numerical results for the kinetic energy ${\lambda }_1$ and chromomagnetic interaction ${\lambda }_2$ are presented. The splitting between spin $1/2$ and $3/2$ doublets derived from our calculation is given; the agreement with the current experiment is good.

Using a soft pion theorem based on chiral symmetry and a $\Delta \mathrm{}\left(1232\right)\mathrm{}$ resonance model, we propose an estimate for the production cross section of low energy pions in the deeply virtual Compton scattering (DVCS) process. In particular, we express the $e\overrightarrow{p}e\gamma \pi N$ processes in terms of generalized parton distributions. We provide estimates of the contamination of the $e\overrightarrow{p}e\gamma p$ DVCS observables due to this associated pion production process when the experimental data are not fully exclusive, for a set of kinematical conditions representative of present or planned experiments at JLab, HERMES, and COMPASS.

We investigate the inclusive production of prompt $J/\psi$ mesons in polarized hadron-hadron, photon-hadron, and photon-photon collisions in the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD) providing all contributing partonic cross sections in analytic form. In the case of photoproduction, we also include the resolved-photon contributions. We present numerical results appropriate for BNL RHIC-Spin, the approved SLAC fixed-target experiment E161, and the $e^{+}{e}^{-}$ and $\gamma \gamma$ modes of DESY TESLA. Specifically, we assess the feasibility to access the spin-dependent parton distributions in the polarized proton and photon. We also point out that preliminary data on $J/\psi$ inclusive production taken by the PHENIX Collaboration in unpolarized proton-proton collisions at RHIC tend to favor the NRQCD factorization hypothesis, while they significantly overshoot the theoretical prediction of the color-singlet model at large values of transverse momentum.

In this work the possibility of detecting solar electron antineutrinos produced by a solar core magnetic field from the KamLAND recent observations is investigated. We find a scaling of the antineutrino probability with respect to the magnetic field profile in the sense that the same probability function can be reproduced by any profile with a suitable peak field value. In this way the solar electron antineutrino spectrum can be unambiguously predicted. We use this scaling and the negative results indicated by the KamLAND experiment to obtain upper bounds on the solar electron antineutrino flux. We get ${\phi }_{\overline{\nu }}<3.8\mathrm{}\times {10}^{-3}\phi {(}^8\mathrm{B})$ at 95% C.L. For 90% C.L. this becomes ${\phi }_{\overline{\nu }}<3.4\mathrm{}\times {10}^{-3}\phi {(}^8\mathrm{B}),$ an improvement by a factor of 3–5 with respect to existing bounds. These limits are independent of the detailed structure of the magnetic field in the solar interior. We also derive upper bounds on the peak field value which are uniquely determined for a fixed solar field profile. In the most efficient antineutrino producing case, we get (95% C.L.) an upper limit on the product of the neutrino magnetic moment by the solar field $\mu B<\mathrm{}2.8\mathrm{}\times {10}^{-19}\mathrm{MeV}$ or $B_0<~4.9\times {10}^7\mathrm{G}$ for ${\mu }_{\nu }{=10\mathrm{}}^{-12}{\mu }_B.$

We suggest replacing measurements of the individual cross sections for the production of $W+N$ jets and $Z+N$ jets in searches for new high-energy phenomena at hadron colliders by the precision measurement of the ratios $(W+0\mathrm{}\mathrm{jet})/(Z+0\mathrm{}\mathrm{jet}),(W+1\mathrm{}\mathrm{jet})/(Z+1\mathrm{}\mathrm{jet}),(W+2\mathrm{}\mathrm{jets})/(Z+2\mathrm{}\mathrm{jets}),\dots ,(W+N\mathrm{jets})/(Z+N\mathrm{jets}),$ with N as large as 6 (the number of jets in $t\overline{t}H).\mathrm{}$ These ratios can also be formed for the case where one or more of the jets is tagged as a b or a c quark. Existing measurements of the individual cross sections for $\overrightarrow{W}e\nu +N$ jets at the Fermilab Tevatron have systematic uncertainties that grow rapidly with N, being dominated by uncertainties in the identification of jets and the jet energy scale. These systematics, and also those associated with the luminosity, parton distribution functions (PDF’s), detector acceptance and efficiencies, and systematics of jet finding and b tagging, are expected to substantially cancel in calculating the ratio of W to Z production in each N-jet channel, allowing a greater sensitivity to new contributions in these channels in run II at the Tevatron and at the CERN LHC.

We consider the mixing of muon and tau neutrinos with sterile fermion fields propagating in extra dimensions in the context of core collapse supernova physics, extending the analysis of the electron neutrino case done in a previous work. We show that the potentially dramatic modifications to the supernova evolution are prevented by a mechanism of feedback, so that no severe bounds on the parameters of the extra dimensions need to be imposed. Nevertheless, the supernova core evolution is significantly modified. We discuss the consequences on the delayed explosion mechanism and the compatibility with the SN 1987A signal. Then, for the cases of both ${\nu }_{\mu ,\tau }$ and ${\nu }_e$ mixing with bulk fermions, we analyze the distinctive features of the signal on Earth.

The quasinormal-mode spectrum of the Schwarzschild–de Sitter black hole is studied in the limit of near-equal black-hole and cosmological radii. It is found that the mode frequencies agree with the Pöschl-Teller approximation to one more order than previously realized, even though the effective potential does not. Whether the spectrum approaches the limiting one uniformly in the mode index is seen to depend on the chosen units (to the order investigated). A perturbation framework is set up in which these issues can be studied to higher order in the future.

In the recently proposed minimal supersymmetric SO(10) model, the neutrino Dirac Yukawa coupling matrix, together with all the other fermion mass matrices, is completely determined once free parameters in the model are appropriately fixed so as to accommodate the recent neutrino oscillation data. Using these unambiguous neutrino Dirac Yukawa couplings, we calculate the lepton flavor violating (LFV) processes and the muon $g-2$ assuming the minimal supergravity scenario. The resultant rates of the LFV processes are found to be large enough to well exceed the proposed future experimental bound, while the magnitude of the muon $g-2$ can be within the recent result of the Brookhaven E821 experiment. Furthermore, we find that there exists a parameter region which can simultaneously realize the neutralino cold dark matter abundance consistent with the recent Wilkinson microwave anisotropy probe data.

We investigate the general relativistic collapse of spherically symmetric, massless spin-$\frac{1}{2}$ fields at the threshold of black hole formation. A spherically symmetric system is constructed from two spin-$\frac{1}{2}$ fields by forming a spin singlet with no net spin-angular momentum. We study the system numerically and find strong evidence for a type II critical solution at the threshold between dispersal and black hole formation, with an associated mass scaling exponent $\gamma \sim \mathrm{0.26.}$ Although the critical solution is characterized by a continuously self-similar (CSS) geometry, the matter fields exhibit discrete self-similarity with an echoing exponent $\Delta \sim \mathrm{1.34.}$ We then adopt a CSS ansatz and reduce the equations of motion to a set of ODEs. We find a solution of the ODEs that is analytic throughout the solution domain, and show that it corresponds to the critical solution found via dynamical evolutions.

An orbiting black hole binary will generate strong gravitational radiation signatures, making these binaries important candidates for detection in gravitational wave observatories. The gravitational radiation is characterized by the orbital parameters, including the frequency and separation at the innermost stable circular orbit (ISCO). One approach to estimating these parameters relies on a sequence of initial data slices that attempt to capture the physics of the inspiral. Using calculations of the binding energy, several authors have estimated the ISCO parameters using initial data constructed with various algorithms. In this paper we examine this problem using conformally Kerr-Schild initial data. We present convergence results for our initial data solutions, and give data from numerical solutions of the constraint equations representing a range of physical configurations. In a first attempt to understand the physical content of the initial data, we find that the Newtonian binding energy is contained in the superposed Kerr-Schild background before the constraints are solved. We examine some deficiencies with the initial data approach to orbiting binaries, especially touching on the effects of prior motion and spin-orbital coupling of the angular momenta. Making rough estimates of these effects, we find that they are not insignificant compared to the binding energy, leaving some doubt of the utility of using initial data to predict ISCO parameters. In computations of specific initial-data configurations we find spin-specific effects that are consistent with analytical estimates.

Nonperturbative treatments of the UV limit of pure gravity suggest that it admits a stable fixed point with a positive Newton constant and a cosmological constant. We prove that this result is stable under the addition of a scalar field with a generic potential and nonminimal coupling to the scalar curvature. There is a fixed point where the mass and all nonminimal scalar interactions vanish, while the gravitational couplings have values which are almost identical to those in the pure gravity case. We discuss the linearized flow around this fixed point and find that the critical surface is four dimensional. In the presence of other, arbitrary, massless minimally coupled matter fields, the existence of the fixed point, the sign of the cosmological constant, and the dimension of the critical surface depend on the type and number of fields. In particular, for some matter content, there exist polynomial asymptotically free scalar potentials, suggesting a gravitational solution to the well-known problem of triviality.

In this work we study the topologically induced electric self-energy and self-force on a long, straight, wire in two distinct, but similar, spacetimes: (i) the Gott-Hiscock thick cosmic string spacetime, and (ii) the spacetime of a continuous distribution of infinitely thin cosmic strings over a disk of finite radius. In each case we obtain the electric self-energy and self-force both in the internal and external regions of the defect distribution. The self-force is always repulsive, independently of the sign of the charge, and is maximum on the string’s surface, in both cases.

We analyze the quantum corrected geometry and radiation in the scattering of extremal black holes by low-energy neutral matter. We point out the fact that the correlators of local observables inside the horizon are the same as those of the vacuum. Outside the horizon the correlators at late times are much bigger than those of the (thermal) case obtained neglecting the back reaction. This suggests that the corrected Hawking radiation could be compatible with unitarity.

We consider bound states of two baryons (antibaryons) in lattice QCD in a Euclidean formulation. For simplicity, we analyze an $\mathrm{SU}\left(3\right)\mathrm{}$ theory with a single flavor in 2+1 dimensions and two-dimensional Dirac matrices. For a small hopping parameter $0<\mathrm{}\kappa \ll 1$ and large glueball mass, we recently showed the existence of a (anti)baryonlike particle, with an asymptotic mass of the order of $-3\ln \kappa$ and with an isolated dispersion curve, i.e., an upper gap property persisting up to near the meson-baryon threshold, which is of order $-5\ln \kappa .$ Here, we show that there is no baryon-baryon (or antibaryon-antibaryon) bound state solution to the Bethe-Salpeter equation up to the two-baryon threshold, which is approximately $-6\ln \kappa .$