It is well known that there exist many mechanisms that may contribute to neutrinoless double beta decay. By exploiting the fact that the associated nuclear matrix elements are target dependent we show that, given definite experimental results on a sufficient number of targets, one can determine or sufficiently constrain all lepton violating parameters including the mass term. As a specific example we show that, assuming the observation of the $0\nu \beta \beta$ decay in three different nuclei, e.g., $\mathrm{G}{}^{76}\mathrm{e}$, ${}^{100}\mathrm{Mo}$, and ${}^{130}\mathrm{Te}$, and just three lepton number violating mechanisms (light- and heavy-neutrino mass mechanisms as well as the $R$-parity breaking supersymmetry mechanism) being active, there are only four different solutions for the lepton violating parameters, provided that they are relatively real. In particular, our analysis shows that the effective neutrino Majorana mass $|m_{\beta \beta }|$ can be almost uniquely extracted by utilizing other existing constraints (cosmological observations and tritium $\beta$-decay experiments). We also point out the possibility that the nonobservation of the $0\nu \beta \beta$ decay for some isotopes could be in agreement with a value of $|m_{\beta \beta }|$ in the sub-eV region. We thus suggest that it is important to have at least two different $0\nu \beta \beta$-decay experiments for a given nucleus. We note that obtained results are sensitive to the accuracy of measured half-lives and to uncertainties in calculated nuclear matrix elements.

We explore the possibility that, while the Higgs mechanism provides masses to the weak-gauge bosons at the electroweak scale as in the standard model, fermion masses are generated by an unknown mechanism at a higher energy scale. At low energies, the standard model can then be regarded as an effective field theory, where fermion masses explicitly break the electroweak $\mathrm{SU}(2{)}_{\mathrm{L}}\times \mathrm{U}(1{)}_{\mathrm{Y}}$ gauge symmetry. If $\Lambda$ is the renormalization scale where the renormalized Yukawa couplings vanish, then at energies lower than $\Lambda$, effective Yukawa couplings will be radiatively induced by nonzero fermion masses. In this scenario, Higgs boson decays into photons and weak gauge-bosons pairs are in general quite enhanced for a light Higgs. However, depending on $\Lambda$, a substantial decay rate into $b\overline{b}$ can arise that can be of the same order as, or larger than, the enhanced $H\to \gamma \gamma$ rate. A new framework for Higgs searches at hadron colliders is outlined, vector-boson fusion becoming the dominant production mechanism at the CERN LHC, with an important role also played by the $WH/ZH$ associated production. A detailed analysis of the Higgs branching fractions and their implications in Higgs searches is provided, versus the energy scale $\Lambda$.

We demonstrate that a naturally small quantum correction, or the Casimir energy, to the cosmological constant can arise from a massive bulk fermion field in the Randall-Sundrum model. Under the assumption that the ground value of four-dimensional effective cosmological constant is zero, which can only be attained by some other means, we show that its quantum correction originated from the Casimir energy, that is the vacuum energy associated with the nontrivial topology of the extra dimension, can be as small as the observed dark energy scale without fine-tuning of the bulk fermion mass. To ensure the stabilization of the system, we discuss two stabilization mechanisms under this setup. It is found that the Goldberger-Wise mechanism can be successfully introduced in the presence of a massive bulk fermion, without spoiling the smallness of the quantum correction.

We examine two-point correlation functions involving the trace of the energy-momentum tensor in five-dimensional dual gravity theories supported by one or more scalar fields. A prescription for determining bulk channel spectral functions is developed. This prescription generalizes previous work which centered on one scalar field. As an application of these techniques, we investigate the bulk spectral function and corresponding sum rule in the Chamblin-Reall background. We show that, when expressed in terms of the beta function, the sum rule for the Chamblin-Reall background can be written in a form similar to the sum rule in Yang-Mills theory.

Ryu and Takayanagi conjectured a formula for the entanglement (von Neumann) entropy of an arbitrary spatial region in an arbitrary holographic field theory. The von Neumann entropy is a special case of a more general class of entropies called Rényi entropies. Using Euclidean gravity, Fursaev computed the entanglement Rényi entropies (EREs) of an arbitrary spatial region in an arbitrary holographic field theory, and thereby derived the RT formula. We point out, however, that his EREs are incorrect, since his putative saddle points do not in fact solve the Einstein equation. We remedy this situation in the case of two-dimensional conformal field theories (CFTs), considering regions consisting of one or two intervals. For a single interval, the EREs are known for a general CFT; we reproduce them using gravity. For two intervals, the RT formula predicts a phase transition in the entanglement entropy as a function of their separation, and that the mutual information between the intervals vanishes for separations larger than the phase transition point. By computing EREs using gravity and CFT techniques, we find evidence supporting both predictions. We also find evidence that large $N$ symmetric product theories have the same EREs as holographic ones.

Starting from the general cosine form for the axion effective potential, we quantize the axion and show that the result is described by a naturally flat potential, if interactions with other particles are not considered. This feature therefore restores the would-be Goldstone-boson nature of the axion, and we calculate the corresponding vacuum energy density, which does not need to be too large by orders of magnitude compared to dark energy.

We develop the formalism of “general gauge mediation” for five-dimensional theories in a slice of AdS space. A set of current correlators encodes the effect of a supersymmetry breaking hidden sector localized on the IR brane. These current correlators provide a tree-level gaugino mass and loop-level sfermion masses on the UV brane. We also use this formalism to calculate the Casimir energy and masses for bulk hyperscalars. To illustrate this general construction we consider a perturbative hidden sector of generalized messengers coupled to a spurion. For models with large warping, we find that when the AdS warp factor $k$ is less than the characteristic mass scale $M$ of the hidden sector, the whole Kaluza-Klein tower of vector superfields propagate supersymmetry breaking effects to the UV brane. When $M$ is less than $k$, the zero modes dominate.

Using analytic and numerical techniques Nielsen-Olesen vortices, which in the context of Ginzburg-Landau theory are known as Abrikosov vortices of type-II superconductors, are studied for large Ginzburg-Landau parameter $\lambda$. We show that their energy is equal to $(\pi n^2/2)\log \lambda$ to leading order, where $n$ is the winding number of the vortex, and find that the limit of the gauge field can be expressed in terms of the modified Bessel function $K_1$. The leading terms of the asymptotic expansion of the solution are given, and the different contributions to the energy are analyzed.

We propose to regulate the infinities of eternal inflation by relating a late time cutoff in the bulk to a short-distance cutoff on the future boundary. The light-cone time of an event is defined in terms of the volume of its future light cone on the boundary. We seek an intrinsic definition of boundary volumes that makes no reference to bulk structures. This requires taming the fractal geometry of the future boundary and lifting the ambiguity of the conformal factor. We propose to work in the conformal frame in which the boundary Ricci scalar is constant. We explore this proposal in the Friedmann-Robertson-Walker approximation for bubble universes. Remarkably, we find that the future boundary becomes a round three-sphere, with smooth metric on all scales. Our cutoff yields the same relative probabilities as a previous proposal that defined boundary volumes by projection into the bulk along timelike geodesics. Moreover, it is equivalent to an ensemble of causal patches defined without reference to bulk geodesics. It thus yields a holographically motivated and phenomenologically successful measure for eternal inflation.

The baby Skyrme model is studied with a novel choice of potential, $V=\frac{1}{2}{\varphi }_3^2$. This “easy plane” potential vanishes at the equator of the target two-sphere. Hence, in contrast to previously studied cases, the boundary value of the field breaks the residual $SO(2)$ internal symmetry of the model. Consequently, even the unit charge Skyrmion has only discrete symmetry and consists of a bound state of two half lumps. A model of long-range inter-Skyrmion forces is developed wherein a unit Skyrmion is pictured as a single scalar dipole inducing a massless scalar field tangential to the vacuum manifold. This model has the interesting feature that the two-Skyrmion interaction energy depends only on the average orientation of the dipoles relative to the line joining them. Its qualitative predictions are confirmed by numerical simulations. Global energy minimizers of charges $B=1,\dots ,14,18,32$ are found numerically. Up to charge $B=6$, the minimizers have $2B$ half lumps positioned at the vertices of a regular $2B$-gon. For charges $B\ge 7$, rectangular or distorted rectangular arrays of $2B$ half lumps are preferred, as close to square as possible.

All-order spurion-corrected superpropagators and superfield Feynman rules are employed to systematically compute a two-loop corrected effective potential for the O’Raifeartaigh model, that realizes spontaneous supersymmetry breaking. Though the shifted superpropagators are rather nontrivial, superspace techniques may be suitably extended and confirm their efficacy in computing radiative corrections even when supersymmetry breakdown occurs.

We study the cosmology of a covariant Galileon field $\varphi$ with five covariant Lagrangians and confront this theory with the most recent cosmological probes: the type Ia supernovae data (Constitution and Union2 sets), cosmic microwave background (WMAP7), and the baryon acoustic oscillations (SDSS7). In the Galileon cosmology with a late-time de Sitter attractor, there is a tracker that attracts solutions with different initial conditions to a common trajectory. Including the cosmic curvature $K$, we place observational constraints on two distinct cases: (i) the tracker, and (ii) the generic solutions to the equations of motion. We find that the tracker solution can be consistent with the individual observational data, but it is disfavored by the combined data analysis. The generic solutions fare quite well when a nonzero curvature parameter ${\Omega }_K^{(0)}$ is taken into account, but the Akaike and Bayesian information criteria show that they are not particularly favored over the $\Lambda \mathrm{CDM}$ model.

We use the Raychaudhuri equation to probe certain aspects related to the gravitational collapse of a charged medium. The aim is to identify the stresses the Maxwell field exerts on the fluid and discuss their potential implications. Particular attention is given to those stresses that resist contraction. After looking at the general case, we consider the two opposite limits of poor and high electrical conductivity. In the former there are electric fields but no currents, while in the latter the situation is reversed. When the conductivity is low, we find that the main agents acting against the collapse are the Coulomb forces triggered by the presence of an excess charge. At the ideal Magnetohydrodynamic (MHD) limit, on the other hand, the strongest resistance seems to come from the tension of the magnetic forcelines. In either case, we discuss whether and how the aforementioned resisting stresses may halt the contraction and provide a set of conditions making this likely to happen.

One way to produce complete inspiral-merger-ringdown gravitational waveforms from black-hole-binary systems is to connect post-Newtonian (PN) and numerical-relativity (NR) results to create “hybrid” waveforms. Hybrid waveforms are central to the construction of some phenomenological models for gravitational-wave (GW) search templates, and for tests of GW search pipelines. The dominant error source in hybrid waveforms arises from the PN contribution, and can be reduced by increasing the number of NR GW cycles that are included in the hybrid. Hybrid waveforms are considered sufficiently accurate for GW detection if their mismatch error is below 3% (i.e., a fitting factor above 0.97). We address the question of the length requirements of NR waveforms such that the final hybrid waveforms meet this requirement, considering nonspinning binaries with $q=M_2/M_1\in [1,4]$ and equal-mass binaries with $\chi =S_i/M_i^2\in [-0.5,0.5]$. We conclude that, for the cases we study, simulations must contain between three (in the equal-mass nonspinning case) and ten (the $\chi =0.5$ case) orbits before merger, but there is also evidence that these are the regions of parameter space for which the least number of cycles will be needed.

We extend the recent proposal of hidden conformal symmetry to the four-dimensional spacetimes with a rotational parameter and Newman-Unti-Tamburino twist. We consider the wave equation of a massless scalar field in the background of Kerr-Bolt spacetimes and show in the “near region” that the wave equation can be reproduced by the $SL(2,R{)}_L\times SL(2,R{)}_R$ Casimir quadratic operators. Moreover, we compute the microscopic entropy of the dual conformal field theories by the Cardy formula and find a perfect match to the entropy of Kerr-Bolt spacetimes. The absorption cross section of a near region scalar field also matches the microscopic absorption cross section of the dual conformal field theories.

In the present paper, we prove a classification (uniqueness) theorem for stationary, asymptotically flat black hole spacetimes with connected and nondegenerate horizon in 4D Einstein-Maxwell-dilaton theory with an arbitrary dilaton coupling parameter $\alpha$. We show that such black holes are uniquely specified by the length of the horizon interval, angular momentum, electric and magnetic charge, and the value of the dilaton field at infinity when the dilaton coupling parameter satisfies $0\le {\alpha }^2\le 3$. The proof is based on the nonpositivity of the Riemann curvature operator on the space of the potentials. A generalization of the classification theorem for spacetimes with disconnected horizons is also given.

We obtain mass and angular momentum of black holes as conserved charges in three-dimensional new massive gravity, after presenting the explicit expression for the potential of the conserved charges. This confirms the expression of those charges obtained in several ways, in particular, through AdS/CFT correspondence, and shows us that the first law of black hole thermodynamics is valid in these black holes. We also comment about conserved charges in new type black holes with the emphasis on the AdS/CFT correspondence as the guiding principle.

Using the brick-wall method, we study statistical entropy for spherically symmetric black holes in Hořava-Lifshitz gravity. In particular, a Lifshitz scalar field is considered in order to incorporate foliation-preserving diffeomorphism, which eventually gives a modified dispersion relation. Finally, we obtain the area law without the UV cutoff for $z>3$ and discuss some of the consequences in connection with the generalized uncertainty principle.

Determination of whether the Harrison-Zel’dovich spectrum for primordial scalar perturbations is consistent with observations is sensitive to assumptions about the reionization scenario. In light of this result, we revisit constraints on inflationary models using more general reionization scenarios. While the bounds on the tensor-to-scalar ratio are largely unmodified, when different reionization schemes are addressed, hybrid models are back into the inflationary game. In the general reionization picture, we reconstruct both the shape and amplitude of the inflaton potential. We discuss how relaxing the simple reionization restriction affects the reconstruction of the potential through the changes in the constraints on the spectral index, the tensor-to-scalar ratio and the running of the spectral index. We also find that the inclusion of other Cosmic Microwave Background data in addition to the Wilkinson Microwave Anisotropy probe data excludes the very flat potentials typical of models in which the inflationary evolution reaches a late-time attractor, as a consequence of the fact that the running of the spectral index is constrained to be different from zero at 99% confidence level.

We give an explicit, rigorous framework for calculating quantum probabilities in a model theory of quantum gravity. Specifically, we construct the decoherence functional for the Wheeler-DeWitt quantization of a flat Friedmann-Robertson-Walker cosmology with a free, massless, minimally coupled scalar field, thus providing a complete decoherent histories formulation for this quantum cosmological model. The decoherence functional is applied to study predictions concerning the model’s Dirac (relational) observables; the behavior of semiclassical states and superpositions of such states; and to study the singular behavior of quantum Wheeler-DeWitt universes. Within this framework, rigorous formulas are given for calculating the corresponding probabilities from the wave function when those probabilities may be consistently defined, thus replacing earlier heuristics for interpreting the wave function of the universe with explicit constructions. It is shown according to a rigorously formulated standard, and in a quantum-mechanically consistent way, that in this quantization these models are generically singular. Independent of the choice of state we show that the probability for these Wheeler-DeWitt quantum universes to ever encounter a singularity is unity. In addition, the relation between histories formulations of quantum theory and relational Dirac observables is clarified.