The junction conditions for general relativity in the presence of domain walls with intrinsic spin are derived in three and higher dimensions. A stress tensor and a spin current can be defined just by requiring the existence of a well-defined volume element instead of an induced metric, so as to allow for generic torsion sources. In general, when the torsion is localized on the domain wall, it is necessary to relax the continuity of the tangential components of the vielbein. In fact it is found that the spin current is proportional to the jump in the vielbein and the stress-energy tensor is proportional to the jump in the spin connection. The consistency of the junction conditions implies a constraint between the direction of flow of energy and the orientation of the spin. As an application, we derive the circularly symmetric solutions for both the rotating string with tension and the spinning dust string in three dimensions. The rotating string with tension generates a rotating truncated cone outside and a flat space-time with inevitable frame dragging inside. In the case of a string made of spinning dust, in opposition to the previous case no frame dragging is present inside, so that in this sense, the dragging effect can be shielded by considering spinning instead of rotating sources. Both solutions are consistently lifted as cylinders in the four-dimensional case.

In this paper we, first, generalize the quasilocal definition of the stress-energy tensor of Einstein gravity to the case of Lovelock gravity, by introducing the tensorial form of surface terms that make the action well-defined. We also introduce the boundary counterterm that removes the divergences of the action and the conserved quantities of the solutions of Lovelock gravity with flat boundary at constant $t$ and $r$. Second, we obtain the metric of spacetimes generated by brane sources in dimensionally continued gravity through the use of Hamiltonian formalism, and show that these solutions have no curvature singularity and no horizons, but have conic singularity. We show that these asymptotically AdS spacetimes which contain two fundamental constants are complete. Finally we compute the conserved quantities of these solutions through the use of the counterterm method introduced in the first part of the paper.

In cosmological scenarios such as the pre-big bang scenario or the ekpyrotic scenario, a matching condition between the metric perturbations in the pre-big bang phase and those in the post big bang phase is often assumed. Various matching conditions have been considered in the literature. Nevertheless obtaining a scale-invariant CMB spectrum via a concrete mechanism remains impossible. In this paper, we examine this problem from the point of view of local causality. We begin with introducing the notion of local causality and explain how it constrains the form of the matching condition. We then prove a no-go theorem: independent of the details of the matching condition, a scale-invariant spectrum is impossible as long as the local causality condition is satisfied. In our framework, it is easy to show that a violation of local causality around the bounce is needed in order to give a scale-invariant spectrum. We study a specific scenario of this possibility by considering a nonlocal effective theory inspired by noncommutative geometry around the bounce and show that a scale-invariant spectrum is possible. Moreover we demonstrate that the magnitude of the spectrum is compatible with observations if the bounce is assumed to occur at an energy scale which is a few orders of magnitude below the Planckian energy scale.

The possibility of generating neutrino mass through see-saw mechanism involving U(1) chiral Peccei-Quinn and scale symmetries breakdown is discussed. We consider a generic scale invariant model which has three Majorana fermions and a complex scalar singlet, which might be the one responsible for an invisible axion, and we perform a summation of all leading-logarithmic radiative corrections to the tree level potential. The effective potential so obtained is stable and drives the scalar field to a nonzero vacuum expectation value according to the Coleman-Weinberg mechanism. As a result, right-handed neutrinos gain mass at the Peccei-Quinn scale which is suggestive for explaining very light active neutrinos. We illustrate the whole idea with the addition of the standard model, and also a $\mathrm{SU}(3{)}_L\otimes \mathrm{U}(1{)}_X$ model in which the subgroup $\mathrm{SU}(2{)}_L\otimes \mathrm{U}(1{)}_Y$ is constrained to be broken as an effect of the effective potential. This last model presents electric charge quantization as well.

We calculate one-loop renormalization factors of generic $\Delta S=2$ four-quark operators for domain-wall QCD with the plaquette gauge action and the Iwasaki gauge action. The renormalization factors are presented in the modified minimal subtraction $(\overline{\mathrm{MS}})$ scheme with the naive dimensional regularization. As an important application we show how to construct the renormalization factors for the operators contributing to $K^0-{\overline{K}}^0$ mixing in the supersymmetric models with the use of our results.

Motivated by the recent measurement on the upper limit of $B^0\to J/\psi D$ branching ratio, we investigate the $B^0\to J/\psi D^{(\star )}$ and ${\eta }_c{D}^{(\star )}$ decays in the framework of $k_T$ factorization. We find that these pure annihilation ($W$-exchange) decays possess branching ratios of the order ${10}^{-5}\sim {10}^{-7}$, which are just at the corner of being observable at the current running $B$ factories. The measurements of these decay channels may help us to understand the QCD dynamics in the corresponding energy scale, and, especially, the distribution amplitudes of charmonium.

We calculated the matter effect, including both the Earth and supernova, on the detection of neutrinos from type II supernovae at the proposed Daya Bay reactor neutrino experiment. It is found that apart from the dependence on the flip probability $P_H$ inside the supernova and the mass hierarchy of neutrinos, the amount of the Earth matter effect depends on the direction of the incoming supernova neutrinos, and reaches the biggest value when the incident angle of neutrinos is around 93°. In the reaction channel ${\overline{\nu }}_e+p\to e^{+}+n$ the Earth matter effect can be as big as about 12%. For other detection processes the amount of the Earth matter effect is a few per cent.

This work concerns the loss of energy of a material system due to gravitational radiation in Einstein-aether theory—an alternative theory of gravity in which the metric couples to a dynamical, timelike, unit-norm vector field. Derived to lowest post-Newtonian order are wave forms for the metric and vector fields far from a nearly Newtonian system and the rate of energy radiated by the system. The expressions depend on the quadrupole moment of the source, as in standard general relativity, but also contain monopolar and dipolar terms. There exists a one-parameter family of Einstein-aether theories for which only the quadrupolar contribution is present, and for which the expression for the damping rate is identical to that of general relativity to the order worked to here. This family cannot yet be declared observationally viable, since effects due to the strong internal fields of bodies in the actual systems used to test the damping rate have not yet been determined.

We present the results of an analysis of superradiant energy flow due to scalar fields incident on an acoustic black hole. In addition to providing independent confirmation of the recent results in [E. Berti, V. Cardoso, and J. P. S. Lemos, Phys. Rev. D 70, 124006 (2004).], we determine in detail the profile of energy flow everywhere outside the horizon. We confirm explicitly that in a suitable frame the energy flow is inward at the horizon and outward at infinity, as expected on physical grounds.

We investigate quantum tunnelling methods for calculating black hole temperature, specifically the null-geodesic method of Parikh and Wilczek and the Hamilton-Jacobi Ansatz method of Angheben et al. We consider application of these methods to a broad class of spacetimes with event horizons, inlcuding Rindler and nonstatic spacetimes such as Kerr-Newman and Taub-NUT. We obtain a general form for the temperature of Taub-NUT-AdS black holes that is commensurate with other methods. We examine the limitations of these methods for extremal black holes, taking the extremal Reissner-Nordstrom spacetime as a case in point.

We study general properties of attractors for scalar-field dark energy scenarios which possess cosmological scaling solutions. In all such models there exists a scalar-field dominant solution with an energy fraction ${\Omega }_{\varphi }=1$ together with a scaling solution. A general analytic formula is given to derive fixed points relevant to dark energy coupled to dark matter. We investigate the stability of fixed points without specifying the models of dark energy in the presence of nonrelativistic dark matter and provide a general proof that a nonphantom scalar-field dominant solution is unstable when a stable scaling solution exists in the region ${\Omega }_{\varphi }<1$. A phantom scalar-field dominant fixed point is found to be classically stable. We also generalize the analysis to the case of multiple scalar fields and show that for a nonphantom scalar-field assisted acceleration always occurs for all scalar-field models which have scaling solutions. For a phantom field the equation of state approaches that of cosmological constant as we add more scalar fields.

The cosmic 21-cm background frequency spectrum related to the spin-flip transition of neutral hydrogen present during and before the era of reionization is rich in features associated with physical processes that govern transitions between the two spin states. The intervening electrons in foreground galaxy clusters inversely Compton scatter the 21-cm background spectrum and modify it just as the cosmic microwave background (CMB) spectrum is modified by inverse-Compton scattering. Towards typical galaxy clusters at low redshifts, the resulting modification is a few tenths milli-Kelvin correction to the few tens milli-Kelvin temperature of 21-cm signal relative to that of the cosmic microwave background blackbody spectrum. The modifications are mostly associated with sharp changes in the cosmic 21-cm background spectrum such as due to the onset of a Lyman-$\alpha$ radiation field or heating of neutral gas. Though low-frequency radio interferometers that are now planned for 21-cm anisotropy measurements are insensitive to the mean 21-cm spectrum, differential observations of galaxy clusters with these interferometers can be utilized to indirectly establish global features in the 21-cm frequency spectrum. We discuss the feasibility to detect the spectrum modified by clusters and find that, for upcoming interferometers, while a detection towards an individual cluster is challenging, one can average signals over a number of clusters, selected based on the strength of the Sunyave-Zel’dovich effect at high radio frequencies involving CMB scattering alone, to establish the mean 21-cm spectrum.

The one-loop induced top quark decay $t\to u_1{\overline{u}}_2{u}_2$ $(u_i=u,c)$ is calculated in the context of the standard model. The dominant contribution to this top quark decay arises from the Feynman diagrams induced by the off-shell $t{u}_1{g}^{*}$ vertex, whereas the box diagrams are negligibly small. In contrast with the on-shell $t{u}_{1}g$ vertex, which only gives rise to a pure dipolar effect, the off-shell $t{u}_1{g}^{*}$ coupling also involves a monopolar term, which gives a larger contribution than the dipolar one. It is found that the branching ratio for the three-body decay $t\to u_1{\overline{u}}_2{u}_2$ is about of the same order of magnitude of the two-body decay $t\to u_{1}g$, which stems from the fact that the three-body decay is dominated by the monopolar term.

In dense neutrino systems, such as found in the early Universe, or near a supernova core, neutrino flavor evolution is affected by coherent neutrino-neutrino scattering. It has been recently suggested that many-particle quantum entanglement effects may play an essential role in these systems, potentially invalidating the traditional description in terms of a set of single-particle evolution equations. We model the neutrino system by a system of interacting spins, following an earlier work which showed that such a spin system can in some cases be solved exactly [A. Friedland and C. Lunardini, J. High Energy Phys. 10 (2003) 043.]. We extend this work by constructing an exact analytical solution to a more general spin system, including initial states with asymmetric spin distribution and, moreover, not necessarily aligned along the same axis. Our solution exhibits a rich set of behaviors, including coherent oscillations and dephasing and a transition from the classical to quantum regimes. We argue that the classical evolution of the spin system captures the entire coherent behavior of the neutrino system, while the quantum effects in the spin system capture some, but not all, of the neutrino incoherent evolution. By comparing the spin and neutrino systems, we find no evidence for the violation of the accepted one-body description, though the argument involves some subtleties not appreciated before. The analysis in this paper may apply to other two-state systems beyond the neutrino field.

This paper describes a measurement of the top quark mass, $M_{\mathrm{top}}$, with the dynamical likelihood method (DLM) using the CDF II detector at the Fermilab Tevatron. The Tevatron produces top/antitop ($t\overline{t}$) pairs in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV. The data sample used in this analysis was accumulated from March 2002 through August 2004, which corresponds to an integrated luminosity of $318{\mathrm{pb}}^{-1}$. We use the $t\overline{t}$ candidates in the “$\mathrm{\text{lepton}}+\mathrm{\text{jets}}$” decay channel, requiring at least one jet identified as a $b$ quark by finding a displaced secondary vertex. The DLM defines a likelihood for each event based on the differential cross section as a function of $M_{\mathrm{top}}$ per unit phase space volume of the final partons, multiplied by the transfer functions from jet to parton energies. The method takes into account all possible jet combinations in an event, and the likelihood is multiplied event by event to derive the top quark mass by the maximum likelihood method. Using 63 $t\overline{t}$ candidates observed in the data, with 9.2 events expected from background, we measure the top quark mass to be $173.2\genfrac{}{}{0ex}{}{+2.6}{-2.4}(\mathrm{stat}.)\pm 3.2(\mathrm{syst}.)\mathrm{GeV}/c^2$, or $173.2\genfrac{}{}{0ex}{}{+4.1}{-4.0}\mathrm{GeV}/c^2$.

Unstable $D$-branes are central objects in string theory, and exist also in time-dependent backgrounds. In this paper we take first steps to studying brane decay in space-time orbifolds. As a concrete model we focus on the ${\mathbb{R}}^{1,d}/{\mathbb{Z}}_2$ orbifold. We point out that on a space-time orbifold there exist two kinds of $S$-branes, fractional $S$-branes in addition to the usual ones. We investigate their construction in the open string and closed string boundary state approach. As an application of these constructions, we consider a scenario where an unstable brane nucleates at the origin of time of a space-time, its initial energy then converting into energy flux in the form of closed strings. The dual open string description allows for a well-defined description of this process even if it originates at a singular origin of the space-time.

We consider the nontrivial boundary conformal field theory with exactly marginal boundary deformation. In recent years this deformation has been studied in the context of rolling tachyons and $S$-branes in string theory. Here we study the problem directly from an open string point of view, at one loop. We formulate the theory of the ${\mathbb{Z}}_2$ reflection orbifold. To do so, we extend fermionization techniques originally introduced by Polchinski and Thorlacius. We also explain how to perform the open string computations at arbitrary (rational) radius, by consistently constructing the corresponding shift orbifold, and show in what sense these are related to known boundary states. In a companion paper, we use these results in a cosmological context involving decaying branes.

In this paper we use the recently released Type Ia Supernova (SNIa) data to constrain the interactions between the neutrinos and the dark energy scalar fields. In the analysis we take the dark energy scalars to be either quintessencelike or phantomlike. Our results show the data mildly favor a model where the neutrinos couple to a phantomlike dark energy scalar, which implies the equation of state of the coupled system behaves like Quintom scenario in the sense of parameter degeneracy. We find future observations like SNAP are potentially promising to measure the couplings between neutrino and dark energy.

The influence of higher dimensions in noncommutative field theories is considered. For this purpose, we analyze the bosonic sector of a recently proposed six-dimensional $SU(3)$ orbifold model for the electroweak interactions. The corresponding noncommutative theory is constructed by means of the Seiberg-Witten map in 6D. We find in the reduced bosonic interactions in 4D theory couplings which are new with respect to other known 4D noncommutative formulations of the standard model using the Seiberg-Witten map. Phenomenological implications due to the noncommutativity of extra dimensions are explored. In particular, assuming that the commutative model leads to the standard model values, a bound $-5.63\times {10}^{-8}{\mathrm{GeV}}^{-2}<{\theta }^{45}<1.06\times {10}^{-7}{\mathrm{GeV}}^{-2}$ on the corresponding noncommutativity scale is derived from current experimental constraints on the $S$ and $T$ oblique parameters. This bound is used to predict a possibly significant impact of noncommutativity effects of extra dimensions on the rare Higgs boson decay $H\to \gamma \gamma$.

We calculate the vector meson masses in $N_{\mathrm{f}}=2+1$ Wilson chiral perturbation theory at next-to-leading order. Generalizing the framework of heavy vector meson chiral perturbation theory, the quark mass and the lattice cutoff dependence of the vector meson masses is derived. Our chiral order counting assumes that the lattice cutoff artifacts are of the order of the typical pion momenta, $p\sim a{\Lambda }_{\mathrm{QCD}}^2$. This counting scheme is consistent with the one in the pseudoscalar meson sector where the $\mathrm{O}(a^2)$ terms are included in the leading order chiral Lagrangian.