We propose that leptonic $CP$ violation arises from a breaking of the $\mu \mathrm{\text{−}}\tau$ exchange symmetry in the neutrino mass matrix which in turn is indicated by the near maximal atmospheric neutrino mixing and the near zero ${\theta }_{13}$. We find that for the case of a normal hierarchy, present data already restrict the way $CP$ violation may appear in the neutrino mass matrix and there is an interesting correlation between the mixing angle ${\theta }_{13}$, the solar mixing angle ${\theta }_{12}$ and the Dirac $CP$ phase. In the inverted hierarchy only ${\theta }_{13}$ and the Dirac phase are linked. We also discuss the impact of this kind of $CP$ violation on the deviation of the atmospheric mixing from its maximal value. Moreover, if corrections to $\mu \mathrm{\text{−}}\tau$ symmetry arise from the charged lepton sector, where $\mu \mathrm{\text{−}}\tau$ symmetry is known to be broken anyway, we find interesting connections between the $CP$-even and $CP$-odd terms as well. Our predictions are testable in the proposed long baseline neutrino experiments.

With a sample of $232\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ events collected with the BABAR detector, we study the decay $B^{+}\to p\overline{p}{K}^{+}$ excluding charmonium decays to $p\overline{p}$. We measure a branching fraction $\mathcal{B}(B^{+}\to p\overline{p}{K}^{+})=(6.7\pm 0.5\pm 0.4)\times {10}^{-6}$. An enhancement at low $p\overline{p}$ mass is observed and the Dalitz plot asymmetry suggests dominance of the penguin amplitude in this $B$ decay. We search for a pentaquark candidate ${\Theta }^{*++}$ decaying into $p{K}^{+}$ in the mass range 1.43 to $2.00\mathrm{GeV}/c^2$ and set limits on $\mathcal{B}(B^{+}\to {\Theta }^{*++}\overline{p})\times \mathcal{B}({\Theta }^{*++}\to p{K}^{+})$ at the ${10}^{-7}$ level.

Given that the dark matter and dark energy in the Universe affect cosmological observables only gravitationally, their phenomenology may be described by a single stress-energy tensor. True unification however requires a theory that reproduces the successful phenomenology of $\Lambda \mathrm{CDM}$ and that requirement places specific constraints on the stress structure of the matter. We show that a recently proposed unification through an offset quadratic kinetic term for a scalar field is exactly equivalent to a fluid with a closed-form barotropic equation of state plus cosmological constant. The finite pressure at high densities introduces a cutoff in the linear power spectrum, which may alleviate the dark matter substructure problem; we provide a convenient fitting function for such studies. Given that sufficient power must remain to reionize the Universe, the equation of state today is nonrelativistic with $p\propto {\rho }^2$ and a Jeans scale in the parsec regime for all relevant densities. Structure may then be evolved into the nonlinear regime with standard hydrodynamic techniques. In fact, the model is equivalent to the well-studied collisional dark matter with negligible mean free path. If recent observations of the triaxiality of dark matter halos and ram pressure stripping in galaxy clusters are confirmed, this model will be ruled out.

The origin of the cosmic $\gamma$-ray background at 1–20 MeV remains a mystery. We show that $\gamma$-ray emission accompanying annihilation of 20 MeV dark-matter particles explains most of the observed signal. Our model satisfies all of the current observational constraints, and naturally provides the origin of “missing” $\gamma$-ray background at 1–20 MeV and 511 keV line emission from the Galactic center. We conclude that $\gamma$-ray observations support the existence of 20 MeV dark-matter particles. Improved measurements of the $\gamma$-ray background in this energy band undoubtedly test our proposal.

We study lattice QCD with staggered sea and Ginsparg-Wilson valence quarks. The Symanzik effective action for this mixed lattice theory, including the lattice spacing contributions of $\mathcal{O}(a^2)$, is derived. Using this effective theory we construct the leading-order chiral Lagrangian. The masses and decay constants of pseudoscalars containing two Ginsparg-Wilson valence quarks are computed at one-loop order.

When scattering amplitudes are calculated in the double-logarithmic approximation, it is possible to relate the double-logarithmic on-shell and off-shell amplitudes. Explicit relations are obtained for scattering amplitudes in QED, QCD, and the electroweak standard model. The off-shell amplitudes are considered in the hard and the Regge kinematic limits. We compare our results in both the Feynman and Coulomb gauges.

We investigate the one-loop renormalizability of a general $\mathcal{N}=\frac{1}{2}$ supersymmetric gauge theory coupled to chiral matter, and show the existence of an $\mathcal{N}=\frac{1}{2}$ supersymmetric $SU(N)\otimes U(1)$ theory which is renormalizable at one loop.

We employ the recently developed worldline numerics, which combines string-inspired field theory methods with Monte Carlo techniques, to develop an algorithm for the computation of pair-production rates in scalar QED for inhomogeneous background fields. We test the algorithm with the classic Sauter potential, for which we compute the local production rate for the first time. Furthermore, we study the production rate for a superposition of a constant $E$ field and a spatially oscillating field for various oscillation frequencies. Our results reveal that the approximation by a local derivative expansion already fails for frequencies small compared to the electron-mass scale, whereas for strongly oscillating fields a derivative expansion for the averaged field represents an acceptable approximation. The worldline picture makes the nonlocal nature of pair production transparent and facilitates a profound understanding of this important quantum phenomenon.

We consider how well the dark energy equation of state $w$ as a function of redshift $z$ will be measured using current and anticipated experiments. We use a procedure which takes fair account of the uncertainties in the functional dependence of $w$ on $z$, as well as the parameter degeneracies, and avoids the use of strong prior constraints. We apply the procedure to current data from the Wilkinson Microwave Anisotropy Probe, Sloan Digital Sky Survey, and the supernova searches, and obtain results that are consistent with other analyses using different combinations of data sets. The effects of systematic experimental errors and variations in the analysis technique are discussed. Next, we use the same procedure to forecast the dark energy constraints achievable by the end of the decade, assuming 8 years of Wilkinson Microwave Anisotropy Probe data and realistic projections for ground-based measurements of supernovae and weak lensing. We find the $2\sigma$ constraints on the current value of $w$ to be $\Delta w_0(2\sigma )=0.20$, and on $dw/dz$ (between $z=0$ and $z=1$) to be $\Delta w_1(2\sigma )=0.37$. Finally, we compare these limits to other projections in the literature. Most show only a modest improvement; others show a more substantial improvement, but there are serious concerns about systematics. The remaining uncertainty still allows a significant span of competing dark energy models. Most likely, new kinds of measurements, or experiments more sophisticated than those currently planned, are needed to reveal the true nature of dark energy.

We investigate and clarify the role of topology and the issues surrounding the $\epsilon$-regime for staggered quarks. We study unimproved and improved staggered quark Dirac operators on quenched lattice QCD gluon backgrounds generated using a Symanzik-improved gluon action. For the improved Dirac operators we find a clear separation of the spectrum into would-be zero modes and others. The number of would-be zero modes depends on the topological charge as predicted by the continuum index theorem, and the expectation values of their chirality are large for the most improved actions ($\approx 0.7$). The remaining modes have low chirality and show clear signs of clustering into quartets that become degenerate in the continuum limit. We demonstrate that the lattice spacing and volume dependence of the eigenvalues follow expectations. Furthermore, the nonzero modes follow the random matrix theory predictions for all topological charge sectors. The values of the chiral condensate extracted from fits to the theoretical distributions are consistent with each other, and with the results obtained from the total density of eigenvalues using the Banks-Casher relation. We conclude that staggered quarks respond correctly to QCD topology when both fermion and gauge actions are improved.

We construct the general static solution to the supergravity action containing gravity, the dilaton and a set of antisymmetric forms describing the intersecting branes delocalized in the relative transverse dimensions. The solution is obtained by reducing the system to a set of separate Liouville equations (the intersection rules implying the separability); it contains the maximal number of free parameters corresponding to the rank of the differential equations. Imposing the requirement of the absence of naked singularities, we show that the general configurations are restricted to two and only two classes: the usual asymptotically flat intersecting branes, and the intersecting branes some of which are asymptotically flat and some approach the linear dilaton background at infinity. In both cases the configurations are black. These are supposed to be relevant for the description of the thermal phase of the QFT’s in the corresponding Domain-Wall/QFT duality.

The two most popular candidates for dark energy, i.e. a cosmological constant and quintessence, are very difficult to distinguish observationally, mostly because the quintessence field does not have sizable fluctuations. We study a scalar field model for dark energy in which the scalar field is invariant under reflection symmetry $\varphi \to -\varphi$. Under general assumptions, there is a phase transition at late times ($z\lesssim 0.5$). Before the phase transition, the field behaves as a cosmological constant. After the phase transition, a time-dependent $\varphi$-condensate forms, the field couples with dark matter and develops sizable perturbations tracking those of dark matter. The background cosmological evolution is in agreement with existing observations, but might be clearly distinguished from that of a cosmological constant by future Supernovae surveys. The growth of cosmological perturbations carries the imprint of the phase transition, however a nonlinear approach has to be developed in order to study it quantitatively.

We study the thermodynamic and gravitational stability of Kerr anti-de Sitter black holes in five and higher dimensions. We show, in the case of equal rotation parameters, $a_i=a$, that the Kerr-AdS background metrics become stable, both thermodynamically and gravitationally, when the rotation parameters $a_i$ take values comparable to the AdS curvature radius. In turn, a Kerr-AdS black hole can be in thermal equilibrium with the thermal radiation around it only when the rotation parameters become not significantly smaller than the AdS curvature radius. We also find with equal rotation parameters that a Kerr-AdS black hole is thermodynamically favored against the existence of a thermal AdS space, while the opposite behavior is observed in the case of a single nonzero rotation parameter. The five-dimensional case is however different and also special in that there is no high temperature thermal AdS phase regardless of the choice of rotation parameters. We also verify that at fixed entropy, the temperature of a rotating black hole is always bounded above by that of a nonrotating black hole, in four and five dimensions, but not in six and more dimensions (especially, when the entropy approaches zero or the minimum of entropy does not correspond to the minimum of temperature). In this last context, the six-dimensional case is marginal.

We discuss the cosmological evolution of cosmic strings with time-dependent tension. We show that, in the case that the tension changes as a power of time, the cosmic string network obeys the scaling solution: the characteristic scale of the string network grows with the time. But due to the time dependence of the tension, the ratio of the energy density of infinite strings to that of the background universe is not necessarily constant.

In an analysis of the gravitational lensing by two relativistic cosmic strings, we argue that the formation of closed timelike curves proposed by Gott is unstable in the presence of particles (e.g. the cosmic microwave background radiation). Because of the attractorlike behavior of the closed timelike curve, we argue that this instability is very generic. A single graviton or photon in the vicinity, no matter how soft, is sufficient to bend the strings and prevent the formation of closed timelike curves. We also show that the gravitational lensing due to a moving cosmic string is enhanced by its motion, not suppressed.

We compare the propagation of iron and proton nuclei above ${10}^{19}\mathrm{eV}$ in a structured Universe with source and magnetic field distributions obtained from a large-scale structure simulation and source densities $\sim {10}^{-5}{\mathrm{Mpc}}^{-3}$. All relevant cosmic ray interactions are taken into account, including photo-disintegration and propagation of secondary products. Iron injection predicts spectral shapes different from proton injection which disagree with existing data below $\simeq 30\mathrm{EeV}$. Injection of light nuclei or protons must therefore contribute at these energies. However, at higher energies, existing data are consistent with injection of pure iron with spectral indices between $\sim 2$ and $\sim 2.4$. This allows a significant recovery of the spectrum above $\simeq 100\mathrm{EeV}$, especially in the case of large deflections. Significant autocorrelation and anisotropy, and considerable cosmic variance are also predicted in this energy range. The mean atomic mass fluctuates considerably between different scenarios. At energies below 60 EeV, if the observed $A\gtrsim 35$, magnetic fields must have a negligible effect on propagation. At the highest energies the observed flux will be dominated by only a few sources whose location may be determined by next generation experiments to within 10–20° even if extra-galactic magnetic fields are important.

Resonant annihilation of ultrahigh energy cosmic neutrinos ($\mathrm{UHEC}\nu$) on the cosmic neutrino background ($\mathrm{C}\nu \mathrm{B}$) into $Z$ bosons—the $Z$-burst mechanism—and its associated absorption and emission phenomenology provide a unique, albeit indirect, probe of the $\mathrm{C}\nu \mathrm{B}$ in its present state. In this paper, we examine the implications of gravitational clustering of the $\mathrm{C}\nu \mathrm{B}$ in nearby galaxy clusters for the $Z$-burst phenomenology. In particular, we study the emission features of the $Z$-decay products originating from the Virgo cluster, and the potential of future cosmic ray experiments to observe clustering-enhanced $Z$-burst rates. We find that a detector with an exposure equivalent to three years of observations at the Extreme Universe Space Observatory (EUSO) will very likely measure these enhanced rates together with the associated $\mathrm{UHEC}\nu$ flux, provided that the latter saturates current observational limits and the neutrino masses are quasidegenerate, $m_{{\nu }_i}\gtrsim 0.1\mathrm{eV}$. In the case of $\mathrm{UHEC}\nu$ fluxes below the electromagnetic cascade limit, or a hierarchical neutrino mass spectrum, an experimental sensitivity exceeding that of EUSO by at least 2 orders of magnitude is required to detect the clustering enhancements with any certainty.

We construct new nonextremal rotating black hole solutions in $SO(6)$ gauged five-dimensional supergravity. Our solutions are the first such examples in which the two rotation parameters are independently specifiable, rather than being set equal. The black holes carry charges for all three of the gauge fields in the $U(1{)}^3$ subgroup of $SO(6)$, albeit with only one independent charge parameter. We discuss the BPS limits, showing that these include the first examples of regular supersymmetric black holes with independent angular momenta in gauged supergravity. We also find nonsingular BPS solitons. Finally, we obtain another independent class of new rotating nonextremal black hole solutions with just one nonvanishing rotation parameter, and one nonvanishing charge.

A detailed and general study of the fermionic structure of the 331 models with $\beta$ arbitrary is carried out based on the criterion of cancellation of anomalies. We consider models with an arbitrary number of lepton and quark generations, but which require associating only one lepton and one quark $SU(3{)}_L$ multiplet for each generation, and at most one right-handed singlet per each left-handed fermion. We see that the number of quark left-handed multiplets must be 3 times the number of leptonic left-handed multiplets. Furthermore, we consider a model with four families and $\beta =-1/\sqrt{3}$ where the additional family corresponds to a mirror fermion of the third generation of the standard model. We also show how to generate ansatz about the mass matrices of the fermions according to the phenomenology. In particular, it is possible to get a natural fit for the neutrino hierarchical masses and mixing angles. Moreover, by means of the mixing between the third quark family and its mirror fermion, a possible solution for the $A_{\mathrm{FB}}^b$ discrepancy is obtained.

The branching ratios of the lightest $CP$-even Higgs boson $h^0$ are calculated in the framework of the general two higgs doublet model. Different scenarios are presented taking into account constraints on the flavor changing neutral currents factors obtained in previous works. Plausible scenarios where appear flavor changing processes at tree level like $b\overline{s}$ and $t\overline{c}$ are analyzed for relevant parameters. The loop-induced Higgs couplings to photon pairs can be tested with a photon collider. The number of events of $h^0$ as a resonance in photon colliders are calculated taking into account its corresponding background signal at TESLA, CLIC, and NLC.