We study an $SU(3{)}^2$ axigluon model introduced by Frampton, Shu, and Wang [Phys. Lett. B 683, 294 (2010)] to explain the recent Fermilab Tevatron observation of a significant positive enhancement in the top quark forward-backward asymmetry relative to standard model predictions. First, we demonstrate that data on neutral $B_d$-meson mixing excludes the region of model parameter space where the top asymmetry is predicted to be the largest. Keeping the gauge couplings below the critical value that would lead to fermion condensation imposes further limits at large axigluon mass, while precision electroweak constraints on the model are relatively mild. Furthermore, by considering an extension to an $SU(3{)}^3$ color group, we demonstrate that embedding the model in an extra-dimensional framework can only dilute the axigluon effect on the forward-backward asymmetry. We conclude that axigluon models are unlikely to be the source of the observed top quark asymmetry.

For a bound state internal wave function respecting parity symmetry, it can be rigorously argued that the mean electric dipole moment must be strictly zero. Thus, both the neutron, viewed as a bound state of three quarks, and the water molecule, viewed as a bound state of ten electrons, two protons, and an oxygen nucleus, have zero mean electric dipole moments. Yet, the water molecules are said to have a nonzero dipole moment strength $d=e\Lambda$ with ${\Lambda }_{{\mathrm{H}}_2\mathrm{O}}\approx 0.385\AA$. The neutron may also be said to have an electric dipole moment strength with ${\Lambda }_{\mathrm{neutron}}\approx 0.612\mathrm{fm}$. The neutron analysis can be made experimentally consistent, if one employs a quark-diquark model of neutron structure.

We present a study of $649\pm 35$ $e^{+}{e}^{-}\to c\overline{c}$ events produced at $\sqrt{s}\approx 10.6\mathrm{GeV}$ containing both a ${\Lambda }_c^{+}$ baryon and a ${\overline{\Lambda }}_c^{-}$ antibaryon. The number observed is roughly 4 times that expected if the leading charmed hadron types are uncorrelated, confirming an observation by the CLEO Collaboration. We find a 2-jet topology in these events but very few additional baryons, demonstrating that the primary $c$ and $\overline{c}$ are predominantly contained in a correlated baryon-antibaryon system. In addition to the charmed baryons we observe on average $2.6\pm 0.2$ charged intermediate mesons, predominantly pions, carrying 65% of the remaining energy.

Using only general features of the $S$ matrix and quantum field theory, we prove by induction the Kawai-Lewellen-Tye relations that link products of gauge theory amplitudes to gravity amplitudes at tree level. As a bonus of our analysis, we provide a novel and more symmetric form of these relations. We also establish an infinite tower of new identities between amplitudes in gauge theories.

We discuss nuclear reactions which could play a role in big bang nucleosynthesis. Most of these reactions involve lithium and beryllium isotopes and the rates for some of these have not previously been included in BBN calculations. Few of these reactions are well studied in the laboratory. We also discuss novel effects in these reactions, including thermal population of nuclear target states, resonant enhancement, and nonthermal neutron reaction products. We perform sensitivity studies which show that even given considerable nuclear physics uncertainties, most of these nuclear reactions have minimal leverage on the standard BBN abundance yields of ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$. Although a few have the potential to alter the yields significantly, we argue that this is unlikely.

We study a model with Majorana neutrino masses generated through doubly charged scalars at two-loop level. We give explicit relationships between the neutrino masses and the same sign dilepton decays of the doubly charged scalars. In particular, we demonstrate that in the tribimaximal limit of the neutrino mixings, the absolute neutrino masses and Majorana phases can be extracted through the measurements of the dilepton modes at colliders.

Black-hole-binary coalescence is often divided into three stages: inspiral, merger, and ringdown. The post-Newtonian (PN) approximation treats the inspiral phase, black-hole perturbation (BHP) theory describes the ringdown, and the nonlinear dynamics of space-time characterize the merger. In this paper, we introduce a hybrid method that incorporates elements of PN and BHP theories, and we apply it to the head-on collision of black holes with transverse, antiparallel spins. We compare our approximation technique with a full numerical-relativity simulation, and we find good agreement between the gravitational waveforms and the radiated energy and momentum. Our results suggest that PN and BHP theories may suffice to explain the main features of outgoing gravitational radiation for head-on mergers. This would further imply that linear perturbations to exact black-hole solutions can capture the nonlinear aspects of head-on binary-black-hole mergers accessible to observers far from the collision.

The three-body problem is reexamined in the framework of general relativity. The Newtonian three-body problem admits Euler’s collinear solution, where three bodies move around the common center of mass with the same orbital period and always line up. The solution is unstable. Hence, it is unlikely that such a simple configuration would exist owing to general relativistic forces dependent not only on the masses but also on the velocity of each body. However, we show that the collinear solution remains true with a correction to the spatial separation between masses. Relativistic corrections to the Sun-Jupiter Lagrange points $L_1$, $L_2$, and $L_3$ are also evaluated.

Wormhole geometries in curvature-matter coupled modified gravity are explored, by considering an explicit nonminimal coupling between an arbitrary function of the scalar curvature, $R$, and the Lagrangian density of matter. It is the effective stress-energy tensor containing the coupling between matter and the higher order curvature derivatives that is responsible for the null energy condition violation, and consequently for supporting the respective wormhole geometries. The general restrictions imposed by the null energy condition violation are presented in the presence of a nonminimal $R$-matter coupling. Furthermore, obtaining exact solutions to the gravitational field equations is extremely difficult due to the nonlinearity of the equations, although the problem is mathematically well defined. Thus, we outline several approaches for finding wormhole solutions, and deduce an exact solution by considering a linear $R$ nonmiminal curvature-matter coupling and by considering an explicit monotonically decreasing function for the energy density. Although it is difficult to find exact solutions of matter threading the wormhole satisfying the energy conditions at the throat, an exact solution is found where the nonminimal coupling does indeed minimize the violation of the null energy condition of normal matter at the throat.

We study the hidden conformal symmetry of extremal black holes. We introduce a new set of conformal coordinates to write the $SL(2,R)$ generators. We find that the Laplacian of the scalar field in many extremal black holes, including Kerr(-Newman), Reissner-Nordstrom, warped ${\mathrm{AdS}}_3$, and null warped black holes, could be written in terms of the $SL(2,R)$ quadratic Casimir. This suggests that there exist dual conformal field theory (CFT) descriptions of these black holes. From the conformal coordinates, the temperatures of the dual CFTs could be read directly. For the extremal black hole, the Hawking temperature is vanishing. Correspondingly, only the left (right) temperature of the dual CFT is nonvanishing, and the excitations of the other sector are suppressed. In the probe limit, we compute the scattering amplitudes of the scalar off the extremal black holes and find perfect agreement with the CFT prediction.

We present a new stationary solution to the field equations of Hořava-Lifshitz gravity with the detailed balance condition and for any value of the coupling constant $\lambda >1/3$. This is the generalization of the corresponding spherically symmetric solution earlier found by Lü, Mei, and Pope to include a small amount of angular momentum. For the relativistic value $\lambda =1$, the solution describes slowly rotating AdS type black holes. With a soft violation of the detailed balance condition and for $\lambda =1$, we also find such a generalization for the Schwarzschild type black hole solution of the theory. Finally, using the canonical Hamiltonian approach, we calculate the mass and the angular momentum of these solutions.

We obtain the static spherically symmetric vacuum solutions of Hořava-Lifshitz gravity theory, imposing the detailed balance condition only in the UV limit. We find the solutions in two different coordinate systems, the Painlevé-Gullstrand coordinates and the Poincaré coordinates, to examine the consequences of imposing the projectability condition. The solutions in two coordinate systems are distinct due to the nonrelativistic nature of the Hořava-Lifshitz gravity. In the Painlevé-Gullstrand coordinates compiling with the projectability condition, the solution involves an additional integration constant which yields surplus angle and implies attractive Coulomb force between same charges.

We study the bounds on tensor wave in a class of twisted inflation models, where $D(4+2k)$-branes are wrapped on cycles in the compact manifold and wrap the Kaluza-Klein direction in the corresponding effective field theory. While the lower bound is found to be analogous to that in type IIB models of brane inflation, the upper bound turns out to be significantly different. This is argued for a range of values for the parameter $g_{s}M$ satisfying the self-consistency relation and the WMAP data. Further, we observe that the wrapped $D8$-brane appears to be the most attractive from a cosmological perspective.

We use different particular classes of axially symmetric Szekeres Swiss-cheese models for the study of the apparent dimming of the supernovae of type Ia. We compare the results with those obtained in the corresponding Lemaître-Tolman Swiss-cheese models. Although the quantitative picture is different the qualitative results are comparable, i.e., one cannot fully explain the dimming of the supernovae using small-scale ($\sim 50\mathrm{Mpc}$) inhomogeneities. To fit successfully the data we need structures of order of 500 Mpc size or larger. However, this result might be an artifact due to the use of axial light rays in axially symmetric models. Anyhow, this work is a first step in trying to use Szekeres Swiss-cheese models in cosmology and it will be followed by the study of more physical models with still less symmetry.

We investigate the general group structure of gauge-Higgs unified models. We find that a given embedding of the standard model gauge group will imply the presence of additional light vectors, except for a small set of special cases, which we determine; the arguments presented are independent of the compactification scheme. For this set of models we then find those that can both accommodate quarks and have a vanishing oblique $T$ parameter at tree level. We show that none of the resulting models can have $|s_{\mathrm{w}}|\sim 1/2$ (the sine of the weak-mixing angle) at tree level and briefly discuss possible solutions to this problem.

Guided by considerations of flavor symmetry, we construct a set of exact standard model renormalization group evolution invariants which link quark masses and mixing parameters. We examine their phenomenological implications and infer a simple combination of Yukawa coupling matrices which plays a unique role in the standard model, suggesting a possible new insight into the observed spectrum of quark masses. Our evolution invariants are readily generalized to the leptons in the case of Dirac neutrinos, but do not appear to be relevant for either quarks or leptons in the minimal supersymmetric standard model.

QCD-like theories possess a positively definite fermion determinant at finite baryon chemical potential ${\mu }_B$ and the lattice simulation can be successfully performed. While the chiral perturbation theories are sufficient to describe the Bose condensate at low density, to describe the crossover from Bose-Einstein condensation (BEC) to BCS superfluidity at moderate density we should use some fermionic effective model of QCD, such as the Nambu–Jona-Lasinio model. In this paper, using two-color two-flavor QCD as an example, we examine how the Nambu–Jona-Lasinio model describes the weakly interacting Bose condensate at low density and the BEC-BCS crossover at moderate density. Near the quantum phase transition point ${\mu }_B=m_{\pi }$ ($m_{\pi }$ is the mass of pion/diquark multiplet), the Ginzburg-Landau free energy at the mean-field level can be reduced to the Gross-Pitaevskii free energy describing a weakly repulsive Bose condensate with a diquark-diquark scattering length identical to that predicted by the chiral perturbation theories. The Goldstone mode recovers the Bogoliubov excitation in weakly interacting Bose condensates. The results of in-medium chiral and diquark condensates predicted by chiral perturbation theories are analytically recovered. The BEC-BCS crossover and meson Mott transition at moderate baryon chemical potential as well as the beyond-mean-field corrections are studied. Part of our results can also be applied to real QCD at finite baryon or isospin chemical potential.

We investigate the singlet scalar dark matter (DM) candidate in a left-right symmetric gauge model with two Higgs bidoublets in which the stabilization of the DM particle is induced by the discrete symmetries $P$ and $CP$. According to the observed DM abundance, we predict the DM direct and indirect detection cross sections for the DM mass range from 10 to 500 GeV. We show that the DM indirect detection cross section is not sensitive to the light Higgs mixing and Yukawa couplings except for the resonance regions. The predicted spin-independent DM-nucleon elastic scattering cross section is found to be significantly dependent on the above two factors. Our results show that the future DM direct search experiments can cover the most parts of the allowed parameter space. The PAMELA antiproton data can only exclude two very narrow regions in the two Higgs bidoublets model. It is very difficult to detect the DM direct or indirect signals in the resonance regions due to the Breit-Wigner resonance effect.

Positive-parity spin-$\frac{1}{2}$ excitations of the nucleon are explored in lattice QCD. The variational method is used in this investigation and several correlation matrices are employed. As our focus is on the utility and methodology of the variational approach, we work in the quenched approximation to QCD. Various sweeps of Gaussian fermion-field smearing are applied at the source and at the sink of ${\chi }_1{\overline{\chi }}_1$ and ${\chi }_1{\chi }_2$ correlation functions to obtain a large basis of operators. Using several different approaches for constructing basis interpolators, we demonstrate how improving the basis can split what otherwise might be interpreted as a single state into multiple eigenstates. Consistency of the extracted excited energy states are explored over various dimensions of the correlation matrices. The use of large correlation matrices is emphasized for the reliable extraction of the excited eigenstates of QCD.