We derive exact solutions of the seven-dimensional Einstein-Maxwell equations for a spacetime exhibiting Poincaré invariance along four dimensions and spherical symmetry in the extra dimensions. Such topology generically arises in the context of braneworld models. Our solutions generalize previous results on Ricci-flat spacetimes admitting the two-sphere and are shown to include wormhole configurations. A regular coordinate system suitable to describe the whole spacetime is singled out, and we discuss the physical relevance of the derived solutions.

In the multiverse, as in AdS space, light cones relate bulk points to boundary scales. This holographic UV-IR connection defines a preferred global time cutoff that regulates the divergences of eternal inflation. An entirely different cutoff, the causal patch, arises in the holographic description of black holes. Remarkably, I find evidence that these two regulators define the same probability measure in the multiverse. Initial conditions for the causal patch are controlled by the late-time attractor regime of the global description.

We show that at second order in cosmological perturbation theory vorticity generation is sourced by entropy gradients. This is an extension of Crocco’s theorem to a cosmological setting.

We aim to offer a kind of unifying view on two popular topics in the studies of nonperturbative aspects of Yang-Mills theories in the Landau gauge: the so-called Gribov-Zwanziger approach and the Kugo-Ojima confinement criterion. Borrowing results from statistical thermodynamics, we show that imposing the Kugo-Ojima confinement criterion as a boundary condition leads to a modified yet renormalizable partition function. We verify that the resulting partition function is equivalent with the one obtained by Gribov and Zwanziger, which restricts the domain of integration in the path integral within the first Gribov horizon. The construction of an action implementing a boundary condition allows one to discuss the symmetries of the system in the presence of the boundary. In particular, the conventional Becchi-Rouet-Stora-Tyutin symmetry is softly broken.

We investigate the dark matter annihilation in the brane-world and quintessence scenarios, in which the modified cosmological expansion rate can enhance the thermal relic density of dark matter. According to the observed dark matter abundance, we constrain the thermally averaged annihilation cross section $⟨\sigma v⟩$ in these two scenarios. In addition, the big bang nucleosynthesis and the partial-wave unitarity are also used to place bounds on $⟨\sigma v⟩$. It is found that both scenarios can lead to a large annihilation cross section, so they can be used to explain the recent PAMELA, ATIC, and PPB-BETS anomalies.

The light scalar meson nonet above 1 GeV (i.e., the $a_0$, $K_0^{*}$ and $f_0$) are studied within the framework of QCD sum rules. In conventional QCD sum rules, the calculated masses of this nonet are degenerate, and the mass of $K_0^{*}$ is always larger than the $a_0$ in contradiction with the observed spectrum. After improving the correlation function by including instanton effects, the masses are well separated from each other. In particular, our results show glueball content plays an important role in the underlying structure of $f_0(1500)$. The sensitivity of the results on the instanton density is also discussed.

We consider the production of heavy-quark pairs in the collisions of polarized and unpolarized on-shell photons and present, in analytic form, the fully integrated total cross sections for total photon spins $J_z=0$, $\pm 2$ at next-to-leading-order in QCD. Phenomenological applications include $b\overline{b}$ production, which represents an irreducible background to standard-model intermediate-mass Higgs-boson production, as well as $t\overline{t}$ production.

Light-cone sum rules are used to investigate the electromagnetic form factors of the $\Lambda$ and $\Sigma$ baryons by using the Ioffe-type interpolating currents. The sum rules are affected to some extent by the choice of the interpolating currents from a comparison. Numerical calculations show that the magnetic form factor can be well fitted by the dipole formula for $\Sigma$ but not for $\Lambda$. The magnetic form factor of $\Lambda$ approaches zero with the momentum transfer faster than the dipole formula estimation.

We point out how, in certain models of new physics, the same combination of couplings occurs in the amplitudes for both $D^0\mathrm{\text{−}}{\overline{D}}^0$ mixing and the rare decays $D^0\to {\ell }^{+}{\ell }^{-}$. If the new physics dominates and is responsible for the observed mixing, then a very simple correlation exists between the magnitudes of each; in fact the rates for the decay $D^0\to {\ell }^{+}{\ell }^{-}$ are completely fixed by the mixing. Observation of $D^0\to {\ell }^{+}{\ell }^{-}$ in excess of the standard model prediction could identify new physics contributions to $D^0\mathrm{\text{−}}{\overline{D}}^0$ mixing.

The zero-mass (ZM) parton formalism is widely used in high-energy physics because of its simplicity and historical importance, even while massive quarks $(c,b,t)$ are playing an increasingly prominent role in particle phenomenology, including global QCD analyses of parton distributions based on the more precise general-mass (GM) QCD formalism. In view of this dichotomy, we show how the obvious inconsistencies of the conventional implementation of the ZM formalism can be corrected, while preserving the simplicity of its hard matrix elements. The resulting intermediate-mass (IM) scheme for perturbative QCD calculation can be considered either as improved ZM formulation with realistic treatment of heavy-flavor kinematics; or as a simplified GM formulation with approximate ZM hard cross sections. Phenomenologically, global analyses based on IM calculations can effectively reproduce, within the present estimated uncertainty bands, the more correct GM results on parton distributions, as well as their predictions for a wide range of collider processes of current interest.

Unless some unknown symmetry in nature prevents or suppresses a nonminimal coupling in the dark sector, the dark energy field may interact with the pressureless component of dark matter. In this paper, we investigate some cosmological consequences of a general model of interacting dark matter-dark energy characterized by a dimensionless parameter $ϵ$. We derive a coupled scalar field version for this general class of scenarios and carry out a joint statistical analysis involving type Ia supernovae data (Legacy and Constitution sets), measurements of baryon acoustic oscillation peaks at $z=0.20$ (2dFGRS) and $z=0.35$ (SDSS), and measurements of the Hubble evolution $\mathrm{H}(z)$. For the specific case of vacuum decay ($w=-1$), we find that, although physically forbidden, a transfer of energy from dark matter to dark energy is favored by the data.

We compare perturbations in a fluid model of dark energy with those in a scalar field. As compared to the $\Lambda \mathrm{CDM}$ model, large scale matter power spectrum is suppressed in fluid model as well as in a generic quintessence dark energy model. To check the efficacy of fluid description of dark energy in emulating a scalar field, we consider a potential which gives the same background evolution as a fluid with a constant equation of state. We show that for sub-Hubble scales, a fluid model effectively emulates a scalar field model. At larger scales, where dark energy perturbations may play a significant role, the fluid analogy breaks down and the evolution of matter density contrast depends on individual scalar field models.

A modular application of the integration by fractional expansion method for evaluating Feynman diagrams is extended to diagrams that contain loop triangle subdiagrams in their geometry. The technique is based in the replacement of this module or subdiagram by its corresponding multiregion expansion (MRE), which in turn is obtained from Schwinger’s parametric representation of the diagram. The result is a topological reduction, transforming the triangular loop into an equivalent vertex, which simplifies the search for the MRE of the complete diagram. This procedure has important advantages with respect to considering the parametric representation of the whole diagram: the obtained MRE is reduced, and the resulting hypergeometric series tends to have smaller multiplicity.

Recent results suggest that multi-Skyrmions stabilized by $\omega$ mesons have very similar properties to those stabilized by the Skyrme term. In this paper we present the results of a detailed numerical investigation of a $(2+1)$-dimensional analogue of this situation. Namely, we compute solitons in an $O(3)$ $\sigma$ model coupled to a massive vector meson and compare the results to baby Skyrmions, which are solitons in an $O(3)$ $\sigma$ model including a Skyrme term. We find that multisolitons in the vector meson model are surprisingly similar to those in the baby Skyrme model, and we explain this correspondence using a simple derivative expansion.

We introduce Weyl’s scale symmetry into the standard model as a local symmetry. This necessarily introduces gravitational interactions in addition to the local scale invariance group $\tilde{U}(1)$ and the standard model groups $SU(3)\times SU(2)\times U(1)$. The only other new ingredients are a new scalar field $\sigma$ and the gauge field for $\tilde{U}(1)$ we call the Weylon. A noteworthy feature is that the system admits the Stückelberg-type compensator. The $\sigma$ couples to the scalar curvature as $(-\zeta /2){\sigma }^{2}R$ and is in turn related to a Stückelberg-type compensator $\phi$ by $\sigma \equiv M_{\mathrm{P}}{e}^{-\phi /M_{\mathrm{P}}}$ with the Planck mass $M_{\mathrm{P}}$. The particular gauge $\phi =0$ in the Stückelberg formalism corresponds to $\sigma =M_{\mathrm{P}}$, and the Hilbert action is induced automatically. In this sense, our model presents yet another mechanism for breaking scale invariance at the classical level. We show that our model naturally accommodates the chaotic inflation scenario with no extra field.

Black hole binaries on noneccentric orbits form an important subclass of gravitational wave sources, but it is a nontrivial issue to construct numerical initial data with minimal initial eccentricity for numerical simulations. We compute post-Newtonian orbital parameters for quasispherical orbits using the method of Buonanno, Chen and Damour, (2006) and examine the resulting eccentricity in numerical simulations. Four different methods are studied resulting from the choice of Taylor-expanded or effective-one-body Hamiltonians, and from two choices for the energy flux. For equal-mass, nonspinning binaries the approach succeeds in obtaining low-eccentricity numerical initial data with an eccentricity of about $e=0.002$ for rather small initial separations of $D\gtrsim 10M$. The eccentricity increases for unequal masses and for spinning black holes, but remains smaller than that obtained from previous post-Newtonian approaches. The effective-one-body Hamiltonian offers advantages for decreasing initial separation as expected, but in the context of this study also performs significantly better than the Taylor-expanded Hamiltonian for binaries with spin. For mass ratio $4:1$ and vanishing spin, the eccentricity reaches $e=0.004$. For mass ratio $1:1$ and aligned spins of size $0.85M^2$ the eccentricity is about $e=0.07$ for the Taylor method and $e=0.014$ for the effective-one-body method.

We consider the modified gravity whose action represents itself as a sum of the usual Einstein-Hilbert action and the gravitational Chern-Simons term and show that the Gödel metric solves the modified equations of motion, thus proving that the closed timelike curves whose presence is characteristic for the Gödel solution are not forbidden in the case of the Chern-Simons modified gravity as well.

We solve a renormalized Wheeler-DeWitt equation for Einstein gravity in $D+1$ dimensions with $D=\mathrm{\text{odd}}$ in the strong coupling limit, which is expected to be suited to probe quantum geometry at short distances, in order to test Hořava’s idea that quantum gravity at short distances will be described by a nonrelativistic system with dynamical critical exponent $z>1$. Our results support the idea and show that the Wheeler-DeWitt equation possesses a solution associated with a $z=2$ Lifshitz point but no other $z>2$ solutions to leading order of the strong coupling expansion.

The near isotropy of the cosmic microwave background (CMB) is considered to be the strongest indication for the homogeneity and isotropy of the Universe, a cornerstone of most cosmological analysis. We derive new theorems which extend the Ehlers-Geren-Sachs result that an isotropic CMB implies that the Universe is either stationary or homogeneous and isotropic, and its generalization to the almost isotropic case. We discuss why the theorems do not apply to the real Universe, and why the CMB observations do not imply that the Universe would be nearly homogeneous and isotropic.

In the recently proposed dark left-right gauge model (DLRM) of particle interactions, the usual left-handed lepton doublet $(\nu ,e{)}_L$ transforming under $SU(2{)}_L$ is accompanied by the unusual right-handed fermion doublet $(n,e{)}_R$ transforming under $SU(2{)}_R$, where $n_R$ is not the Dirac mass partner of ${\nu }_L$. In this scenario, whereas ${\nu }_L$ is certainly a neutrino, $n_R$ should be considered a scotino, i.e. a dark-matter fermion. Variants of this basic idea are discussed, including its minimal scotogenic realization.