We calculate nuclear matrix elements of neutrinoless double beta decay ($0\nu \beta \beta$) in four different candidate nuclei (${}^{76}\mathrm{Ge}$, ${}^{82}\mathrm{Se}$, ${}^{100}\mathrm{Mo}$, ${}^{130}\mathrm{Te}$) within the quasiparticle random phase approximation and its uncertainties. We assume (up to) four coexisting mechanisms for $0\nu 2\beta$ decay, mediated by light Majorana neutrino exchange ($\nu$), heavy Majorana neutrino exchange ($N$), $R$-parity breaking supersymmetry ($\cancel{R}$), and squark-neutrino $(\tilde{q})$, interfering either constructively or destructively with each other. We find that, unfortunately, current nuclear matrix element uncertainties appear to prevent a robust determination of the relative contribution of each mechanism to the decay amplitude, even assuming accurate measurements of decay lifetimes. The near-degeneracy of $0\nu \beta \beta$ mechanisms is analyzed with simple algebraic techniques, which do not involve assumptions about the statistical distribution of errors. We discuss implications of such degeneracy on prospective searches for absolute neutrino masses.

The multiple scattering formalism is used to extract irreducible $N$-body parts of Green’s functions and Casimir energies describing the interaction of $N$ objects that are not necessarily mutually disjoint. The irreducible $N$-body scattering matrix is expressed in terms of single-body transition matrices. The irreducible $N$-body Casimir energy is the trace of the corresponding irreducible $N$-body part of the Green’s function. This formalism requires the solution of a set of linear integral equations. The irreducible three-body Green’s function and the corresponding Casimir energy of a massless scalar field interacting with potentials are obtained and evaluated for three parallel semitransparent plates. When Dirichlet boundary conditions are imposed on a plate the Green’s function and Casimir energy decouple into contributions from two disjoint regions. We also consider weakly interacting triangular and parabolic wedges placed atop a Dirichlet plate. The irreducible three-body Casimir energy of a triangular and parabolic wedge is minimal when the shorter side of the wedge is perpendicular to the Dirichlet plate. The irreducible three-body contribution to the vacuum energy is finite and positive in all the cases studied.

We investigate the possibility that dark matter is a mixture of two noninteracting perfect fluids, with different four-velocities and thermodynamic parameters. The two-fluid model can be described as an effective single anisotropic fluid, with distinct radial and tangential pressures. The basic equations describing the equilibrium structure of the two-fluid dark matter model, and of the tangential velocity of test particles in stable circular orbits, are obtained for the case of a spherically symmetric static geometry. By assuming a nonrelativistic kinetic model for the dark matter particles, the density profile and the tangential velocity of the dark matter mixture are obtained by numerically integrating the gravitational field equations. The cosmological implications of the model are also briefly considered, and it is shown that the anisotropic two-fluid model isotropizes in the large-time limit.

We constrain a stochastic background of a primordial magnetic field (PMF) by its contribution to the angular power spectrum of cosmic microwave background anisotropies. We parametrize such a stochastic background by a power-law spectrum with index $n_B$ and by its Gaussian smoothed amplitude $B_{\lambda }$ on a comoving length $\lambda$. We give an approximation for the spectra of the relevant correlators of the energy-momentum of the stochastic background of PMF for any $n_B$. By using the WMAP 7 yr data in combination with ACBAR, BICEP, and QUaD, we obtain the constraint $B_{1\mathrm{Mpc}}<5.0\mathrm{nG}$ at the 95% confidence level for a stochastic background of a nonhelical PMF. We discuss the relative importance of the scalar and vector contributions to CMB anisotropies in obtaining these constraints. We then forecast Planck capabilities in constraining $B_{1\mathrm{Mpc}}$.

We analyze the decay $B^0\to K^{+}{\pi }^{-}{\pi }^0$ with a sample of $4.54\times {10}^8$ $B\overline{B}$ events collected by the BABAR detector at the PEP-II asymmetric-energy $B$ factory at SLAC, and extract the complex amplitudes of seven interfering resonances over the Dalitz plot. These results are combined with amplitudes measured in $B^0\to K_S^0{\pi }^{+}{\pi }^{-}$ decays to construct isospin amplitudes from $B^0\to K^{*}\pi$ and $B^0\to \rho K$ decays. We measure the phase of the isospin amplitude ${\Phi }_{3/2}$, useful in constraining the Cabibbo-Kobayashi-Maskawa unitarity triangle angle $\gamma$ and evaluate a $CP$ rate asymmetry sum rule sensitive to the presence of new physics operators. We measure direct $CP$ violation in $B^0\to K^{*+}{\pi }^{-}$ decays at the level of $3\sigma$ when measurements from both $B^0\to K^{+}{\pi }^{-}{\pi }^0$ and $B^0\to K_S^0{\pi }^{+}{\pi }^{-}$ decays are combined.

We propose a way to introduce the currents responsible for the chiral magnetic effect, and similar phenomena, into the AdS/CFT description. Such currents are thought to occur in heavy ion collisions due to topologically nontrivial field configurations and in dense stars due to beta decay. They may be responsible for the $\mathcal{P}$ and $\mathcal{C}\mathcal{P}$ odd effects seen at RHIC and the anomalously large velocities observed in some pulsars. We discuss the boundary conditions that allow the phenomenon to exist in real systems and show how one would introduce similar boundary conditions into a holographic model of QCD such that the current is reproduced.

One of the popular modifications to the theory of general relativity is nondynamical Chern-Simons (CS) gravity, in which the metric is coupled to an externally prescribed scalar field. Setting accurate constraints to the parameters of the theory is important owing to their implications for the scalar field and/or the underlying fundamental theory. The current best constraints rely on measurements of the periastron precession rate in the double-binary-pulsar system and place a very tight bound on the characteristic CS length scale $k_{\mathrm{cs}}^{-1}\lesssim 3\times {10}^{-9}\mathrm{km}$. This paper considers several effects that were not accounted for when deriving this bound and lead to a substantial suppression of the predicted rate of periastron precession. It is shown, in particular, that the point-mass approximation for extended test bodies does not apply in this case. The constraint to the characteristic CS length scale is revised to $k_{\mathrm{cs}}^{-1}\lesssim 0.4\mathrm{km}$, 8 orders of magnitude weaker than what was previously found.

A de Sitter (dS) brane on the boundary between two five-dimensional spacetimes is determined. We consider asymmetric scenarios with ${\mathrm{AdS}}_5$ (anti-de Sitter) vacua at each side of the dS brane; and as a result, a resonant mode inside of the spectrum of the gravitational fluctuations is found. We analyze the deviations to the Newtonian potential generated by the gravitational excitations, finding that, for scenarios with large values of the cosmological constants, the contribution of the resonant mode is exponentially suppressed. However, when one of the vacua is null, the resonant mode belongs to the light states set of the gravitational fluctuations and five-dimensional gravity is recovered on the dS brane.

We study the classical second law of black hole thermodynamics, for Lovelock theories (other than general relativity), in arbitrary dimensions. Using the standard formula for black hole entropy, we construct scenarios involving the merger of two black holes in which the entropy instantaneously decreases. Our construction involves a Kaluza-Klein compactification down to a dimension in which one of the Lovelock terms is topological. We discuss some open issues in the definition of the second law which might be used to remove this entropy decrease.

We study spherical black hole solutions in Einstein-aether theory, a Lorentz-violating gravitational theory consisting of general relativity with a dynamical unit timelike vector (the “aether”) that defines a preferred timelike direction. These are also solutions to the infrared limit of Hořava-Lifshitz gravity. We explore parameter values of the two theories where all presently known experimental constraints are satisfied, and find that spherical black hole solutions of the type expected to form by gravitational collapse exist for all those parameters. Outside the metric horizon, the deviations away from the Schwarzschild metric are typically no more than a few percent for most of the explored parameter regions, which makes them difficult to observe with electromagnetic probes, but in principle within reach of future gravitational-wave detectors. Remarkably, we find that the solutions possess a universal horizon, not far inside the metric horizon, that traps waves of any speed relative to the aether. A notion of a black hole thus persists in these theories, even in the presence of arbitrarily high propagation speeds.

Cosmological observations on the largest scales exhibit a solid record of unexpected anomalies and alignments, apparently pointing towards a large-scale violation of statistical isotropy. These include a variety of CMB measurements, as well as alignments of quasar polarization vectors. In this paper we explore the possibility that several of the aforementioned largescale correlations are in fact not independent, and can be understood in a coherent way within the framework of a parityodd local Universe, and ultimately related to the nature of dark energy and its interactions with light.

Cosmological evolution of axionic string network is analyzed in terms of field-theoretic simulations in a box of ${512}^3$ grids, which are the largest ever, using a new and more efficient identification scheme of global strings. The scaling parameter is found to be $\xi =0.87\pm 0.14$ in agreement with previous results. The energy spectrum is calculated precisely using a pseudo power spectrum estimator which significantly reduces the error in the mean reciprocal comoving momentum. The resultant constraint on the axion decay constant leads to $f_a\le 3\times {10}^{11}\mathrm{GeV}$. We also discuss implications for the early Universe.

One of the experimental tests of Lorentz invariance violation is to measure the helicity dependence of the propagation velocity of photons originating in distant cosmological obejcts. Using a recent determination of the distance of the gamma-ray burst GRB 041219A, for which a high degree of polarization is observed in the prompt emission, we are able to improve by four orders of magnitude the existing constraint on Lorentz invariance violation, arising from the phenomenon of vacuum birefringence.

We present the complete next-to-leading order (NLO) QCD corrections to $tZ$ associated production induced by the model-independent $tqg$ and $tqZ$ flavor-changing neutral-current couplings at hadron colliders, respectively. Our results show that, for the $tuZ$ coupling the NLO QCD corrections can enhance the total cross sections by about 60% and 42%, and for the $tcZ$ coupling by about 51% and 43% at the Tevatron and LHC, respectively. The NLO corrections, for the $tug$ couplings, can enhance the total cross sections by about 27%, and by about 42% for the $tcg$ coupling at the LHC. We also consider the mixing effects between the $tqg$ and $tqZ$ couplings for this process, which can either be large or small depending on the values of the anomalous couplings. Besides, the NLO corrections reduce the dependence of the total cross sections on the renormalization or factorization scale significantly, which lead to increased confidence on the theoretical predictions. And we also evaluate the NLO corrections to several important kinematic distributions.

We present a recursive method for super Yang-Mills color-ordered $n$-point tree amplitudes based on the cohomology of pure spinor superspace in ten space-time dimensions. The amplitudes are organized into BRST covariant building blocks with diagrammatic interpretation. Manifestly cyclic expressions (no longer than one line each) are explicitly given up to $n=10$ and higher leg generalizations are straightforward.

We show how to construct supersymmetric actions for higher-derivative scalar field theories of the form $P(X,\varphi )$, where $X\equiv -(\partial \varphi {)}^2/2m^4$, within the context of $d=4$, $\mathcal{N}=1$ supersymmetry. This construction is of general use, and is applied to write supersymmetric versions of the Dirac-Born-Infeld action. Our principal application of this formalism is to construct the supersymmetric extension of the ghost-condensate. This allows us to study the interplay between supersymmetry, time-dependent backgrounds and violations of the null energy condition.

The Weyl-Wigner-Groenewold-Moyal formalism of deformation quantization is applied to cosmological models in the minisuperspace. The quantization procedure is performed explicitly for quantum cosmology in a flat minisuperspace. The de Sitter cosmological model is worked out in detail and the computation of the Wigner functions for the Hartle-Hawking, Vilenkin and Linde wave functions are done numerically. The Wigner function is analytically calculated for the Kantowski-Sachs model in (non)commutative quantum cosmology and for string cosmology with dilaton exponential potential. Finally, baby universes solutions are described in this context and the Wigner function is obtained.

Once weakly-interacting massive particles (WIMPs) are unambiguously detected in direct-detection experiments, the challenge will be to determine what one may infer from the data. Here, I examine the prospects for reconstructing the local speed distribution of WIMPs in addition to WIMP particle-physics properties (mass, cross sections) from next-generation cryogenic and liquid-noble direct-detection experiments. I find that the common method of fixing the form of the velocity distribution when estimating constraints on WIMP mass and cross sections means losing out on the information on the speed distribution contained in the data and may lead to biases in the inferred values of the particle-physics parameters. I show that using a more general, empirical form of the speed distribution can lead to good constraints on the speed distribution. Moreover, one can use Bayesian model-selection criteria to determine if a theoretically-inspired functional form for the speed distribution (such as a Maxwell-Boltzmann distribution) fits better than an empirical model. The shape of the degeneracy between WIMP mass and cross sections and their offset from the true values of those parameters depends on the hypothesis for the speed distribution, which has significant implications for consistency checks between direct-detection and collider data. In addition, I find that the uncertainties on theoretical parameters depends sensitively on the upper end of the energy range used for WIMP searches. Better constraints on the WIMP particle-physics parameters and speed distribution are obtained if the WIMP search is extended to higher energy ($\sim 1\mathrm{MeV}$).

We present a complete study of the one graviton-two neutral gauge bosons vertex at 1-loop level in the electroweak theory. This vertex provides the leading contribution to the interaction between the standard model and gravity, mediated by the trace anomaly, at first order in the inverse Planck mass and at second order in the electroweak expansion. At the same time, these corrections are significant for precision studies of models with low scale gravity at the LHC. We show, in analogy with previous results in the QED and QCD cases, that the anomalous interaction between gravity and the gauge current of the standard model, due to the trace anomaly, is mediated, in each gauge-invariant sector, by effective massless scalar degrees of freedom. We derive the Ward and Slavnov-Taylor identities characterizing the vertex. Our analysis includes the contributions from the improvements of the scalar sector, induced by a conformally coupled Higgs sector in curved space.

In this paper we extend the hydrodynamic results of {A. Fabbri and C. Mayoral, Phys. Rev. D 83, 124016 (2011).} and study, analytically, the propagation of Bogoliubov phonons on top of Bose-Einstein condensates with steplike discontinuities in the speed of sound by taking into account dispersion effects. We focus on the Hawking signal in the density-density correlations in the formation of acoustic black-hole-like configurations.