Recently, the vacuum energy of the QCD ghost field in a time-dependent background was proposed as a kind of dark energy candidate called the ghost dark energy model (GDE) to explain the acceleration of the Universe. In this model, the energy density of the dark energy is proportional to the Hubble parameter $H$, which is also regarded as the Hawking temperature on the Hubble horizon of the Friedmann-Robertson-Walker Universe. In this paper, the statefinder and $Om$ diagnostics are applied to the GDE models, and the differences among them are significant during the time of transition. And at that time, the viscosity plays an important role. Furthermore, we find that once the viscosity is taken into account, the age problem of Universe could be alleviated. We also perform a constraint on the GDE models with and without bulk viscosity by using the Markov Chain Monte Carlo method and the combined latest observational data from the type Ia supernova compilations including Union2.1(580) and Union2(557), cosmic microwave background, baryon acoustic oscillation, and the observational Hubble parameter data.

We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a $(20,20){\mathrm{M}}_{\odot }$ coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for nonspinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with nonspinning components of mass between 19 and $28{\mathrm{M}}_{\odot }$ of $3.3\times {10}^{-7}$ mergers ${\mathrm{Mpc}}^{-3}{\mathrm{yr}}^{-1}$.

The aim of this paper is to investigate an efficient strategy that allows one to obtain $\pi \pi$ phase shifts and $\rho$ meson properties from QCD lattice data with high precision. For this purpose we evaluate the levels of the $\pi \pi$ system in the $\rho$ channel in finite volume using chiral unitary theory. We investigate the dependence on the $\pi$ mass and compare this with other approaches which use QCD lattice calculations and effective theories. We also illustrate the errors induced by using the conventional Lüscher approach instead of a more accurate one that was recently developed that takes into account exactly the relativistic two-meson propagators. Finally, we make use of this latter approach to solve the inverse problem, getting $\pi \pi$ phase shifts from “synthetic” lattice data, providing an optimal strategy and showing which accuracy is needed in these data to obtain the $\rho$ properties with a desired accuracy.

In the absence of interaction, it is well known that the Kogut-Susskind regularizations of fermions in the spin and flavor basis are equivalent to each other. In this paper, we clarify the difference between the two formulations in the presence of interaction with gauge fields. We then derive an explicit expression of the transfer matrix in the spin basis by a unitary transformation on that one in the flavor basis which is known. The essential key ingredient is the explicit construction of the fermion Fock space for variables which live on blocks. Therefore, the transfer matrix generates time translations of two lattice units.

Because at the tree level $B_s\to K^{+}{K}^{-}$ is Cabibbo triple suppressed, so its branching ratio should be smaller than that of $B_s\to {\pi }^{+}{K}^{-}$. The measurements present a reversed ratio as $R=\mathcal{B}(B_s\to {\pi }^{+}{K}^{-})/\mathcal{B}(B_s\to K^{+}{K}^{-})\sim 4.9/33$. Therefore, it has been suggested that the transition $B_s\to K^{+}{K}^{-}$ is dominated by the penguin mechanism, which is proportional to $V_{cb}{V}_{cs}^{*}$. In this work, we show that an extra contribution from the final state interaction to $B_s\to K^{+}{K}^{-}$ via sequential processes $B_s\to D_{(s)}^{(*)}{\overline{D}}_s^{(*)}\to K^{+}{K}^{-}$ is also substantial and should be superposed on the penguin contribution. Indeed, taking into account the final state interaction effects, the theoretical prediction on $R$ is well consistent with the data.

We study a supersymmetric version of the type-III seesaw mechanism considering two variants of the model: a minimal version for explaining neutrino data with only two copies of $\mathbf{24}$ superfields and a model with three generations of $\mathbf{24}$-plets. The latter predicts, in general, rates for $\mu \to e\gamma$ inconsistent with experimental data. However, this bound can be evaded if certain special conditions within the neutrino sector are fulfilled. In the case of two $\mathbf{24}$-plets, lepton flavor violation constraints can be satisfied much more easily. After specifying the corresponding regions in the minimal supergravity parameter space, we show that under favorable conditions one can test the corresponding flavor structures in the leptonic sector at the LHC. For this we perform Monte Carlo studies for the signals, also taking into account the supersymmetry background. We find that it is only of minor importance for the scenarios studied here.

We present a spinning hairy black hole in gravity minimally coupled to a self-interacting real scalar field in three spacetime dimensions. The black hole is characterized by having a single horizon that encloses a curvature singularity and the scalar field is regular everywhere. The mass and angular momentum are shown to be finite. The presence of a scalar field with a slower falloff at infinity leads an anti–de Sitter asymptotic behavior that differs from the one found by Brown and Henneaux but has the same symmetry group as in pure gravity. A scalar soliton, which is a finite mass regular solution devoid of integration constants, plays the role of the ground state. The existence of this soliton is the key to deriving the semiclassical entropy of the rotating hairy black hole using the counting of microscopic states provided by the Cardy formula.

We obtain Bogomolny-Prasad-Sommerfield ${\mathbb{Z}}_2$ monopole solutions in Yang-Mills-Higgs theories with the gauge group $SU(n)$ broken to $\mathrm{Spin}(n)/{\mathbb{Z}}_2$ by a scalar field in the $n\otimes n$ representation. We show that the magnetic weights of the so-called fundamental ${\mathbb{Z}}_2$ monopoles correspond to the weights of the defining representation of the dual algebra $so(n{)}^{\vee }$, and the masses of the nonfundamental Bogomolny-Prasad-Sommerfield ${\mathbb{Z}}_2$ monopoles are equal to the sum of the masses of the constituent fundamental monopoles. We also show that the vacua responsible for the existence of these ${\mathbb{Z}}_2$ monopoles are present in the Higgs branch of a class of $\mathcal{N}=2$ $SU(n)$ superconformal field theories. We analyze some dualities these monopoles may satisfy.

We study lepton asymmetry evolution in plasma of the early Universe before the electroweak phase transition (EWPT) accounting for chirality flip processes via Higgs decays (inverse decays) entering equilibrium at temperatures below $T_{\mathrm{RL}}\simeq 10\mathrm{TeV}$, $T_{\mathrm{EW}}<T<T_{\mathrm{RL}}$. We solve appropriate kinetic equations for leptons and Higgs bosons taking into account the lepton number violation due to Abelian anomalies for right and left electrons and neutrinos in the self-consistent hypercharge field obeying Maxwell equations modified by the contribution of the Standard Model of electroweak interactions. The violation of left lepton numbers and the corresponding violation of the baryon number due to sphaleron processes in symmetric phase is taken into account as well. Assuming the Chern-Simons wave configuration of the seed hypercharge field, we get the estimates of baryon and lepton asymmetries evolved from the primordial right electron asymmetry existing alone as partial asymmetry at $T\ge T_{\mathrm{RL}}$. One finds a strong dependence of the asymmetries on the Chern-Simons wave number. We predict a nonzero chiral asymmetry $\Delta \mu ={\mu }_{e_{\mathrm{R}}}-{\mu }_{e_{\mathrm{L}}}\ne 0$ in this scenario evolved down to the EWPT moment that can be used as an initial value for the Maxwellian field evolution after EWPT.

We show that magnetic fields have the potential to significantly enhance a recently proposed light-shining-through-walls scenario in quantum-field theories with photons coupling to minicharged particles. Suggesting a dedicated laboratory experiment, we demonstrate that this particular tunneling scenario could provide access to a parameter regime competitive with the currently best direct laboratory limits on minicharged fermions below the meV regime. With present day technology, such an experiment has the potential to even overcome the best model-independent cosmological bounds on minicharged fermions with masses below $\mathcal{O}({10}^{-4})\mathrm{eV}$.

Recently, we have demonstrated that for a certain class of Casimir-type systems (“devices”) the energy of zero-point vacuum fluctuations reaches its global minimum when the device rotates about a certain axis rather than remains static. This rotational vacuum effect may lead to the emergence of permanently rotating objects provided the negative rotational energy of zero-point fluctuations cancels the positive rotational energy of the device itself. In this paper, we show that for massless electrically charged particles the rotational vacuum effect should be drastically (astronomically) enhanced in the presence of a magnetic field. As an illustration, we show that in a background of experimentally available magnetic fields the zero-point energy of massless excitations in rotating torus-shaped doped carbon nanotubes may indeed overwhelm the classical energy of rotation for certain angular frequencies so that the permanently rotating state is energetically favored. The suggested “zero-point-driven” devices—which have no internally moving parts—correspond to a perpetuum mobile of a new, fourth kind: They do not produce any work despite the fact that their equilibrium (ground) state corresponds to a permanent rotation even in the presence of an external environment. We show that our proposal is consistent with the laws of thermodynamics.

The weak cosmic censorship conjecture asserts that spacetime singularities that arise in gravitational collapse are always hidden inside of black holes, invisible to distant observers. This conjecture, put forward by Penrose more than four decades ago, is widely believed to be one of the basic principles of nature. However, a complete proof of this hypothesis is still lacking and the validity of the conjecture has therefore remained one of the most important open questions in general relativity. In this study we analyze a gedanken experiment that is designed to challenge cosmic censorship by trying to overcharge a Reissner-Nordström black hole: a charged shell is lowered adiabatically into the charged black hole. The mass energy delivered to the black hole can be redshifted by letting the dropping point of the shell approach the black-hole horizon. On the other hand, the electric charge of the shell is not redshifted by the gravitational field of the black hole. It therefore seems, at first sight, that the charged shell is not hindered from entering the black hole, overcharging it and removing its horizon. However, in the present study we prove that the exposure of a naked singularity to distant observers is actually excluded due to the formation of a new (and larger) horizon around the original black hole. Moreover, we shall prove that this new horizon is already formed before the charged shell crosses the original black-hole horizon. This result, which seems to have been previously overlooked, guarantees the validity of the weak cosmic censorship conjecture in this type of gedanken experiments.

A simple black-hole-ring system is proposed as a toy model for the two-body problem in general relativity. This toy-model yields the fractional shift $\Delta {\Omega }_{\mathrm{isco}}/{\Omega }_{\mathrm{isco}}=\frac{29}{81\sqrt{2}}\eta$ in the Schwarzschild ISCO (innermost stable circular orbit) frequency, where $\eta \equiv m/M_{\mathrm{ir}}\ll 1$ is the dimensionless ratio between the mass of the particle and the irreducible mass of the black hole. Our model suggests that the second-order spin-orbit interaction between the black hole and the orbiting particle (the dragging of inertial frames) is the main element determining the observed value of the ISCO shift.

We explore the degeneracy between mass and spin in gravitational waveforms emitted by black-hole-binary coalescences. We focus on spin-aligned waveforms and obtain our results using phenomenological models that were tuned to numerical-relativity simulations. A degeneracy is known for low-mass binaries (particularly neutron-star binaries), where gravitational-wave detectors are sensitive to only the inspiral phase, and the waveform can be modeled by post-Newtonian theory. Here, we consider black-hole binaries, where detectors will also be sensitive to the merger and ringdown, and demonstrate that the degeneracy persists across a broad mass range. At low masses, the degeneracy is between mass ratio and the black-hole spins, with chirp mass accurately determined. At higher masses, the degeneracy persists but is not so clearly characterized by constant chirp mass as the merger and ringdown become more significant. We consider the importance of this degeneracy both for performing searches (including searches where only nonspinning templates are used) and in parameter extraction from observed systems. We compare observational capabilities between the early ($\sim 2015$) and final (2018 onwards) versions of the Advanced LIGO detector.

Black hole quasinormal frequencies are complex numbers that encode information on how a black hole relaxes after it has been perturbed and depend on the features of the geometry and on the type of perturbations. On the one hand, the examples studied so far in the literature focused on the case of black hole geometries with singularities in their interior. On the other hand, it is expected that quantum or classical modifications of general relativity may correct the pathological singular behavior of classical black hole solutions. Despite the fact that we do not have at hand a complete theory of quantum gravity, regular black hole solutions can be constructed by coupling gravity to an external form of matter, sometimes modeled by one form or another of nonlinear electrodynamics. It is therefore relevant to compute quasinormal frequencies for these regular solutions and see how differently, from the ordinary ones, regular black holes ring. In this paper, we take a step in this direction and, by computing the quasinormal frequencies, study the quasinormal modes of neutral and charged scalar field perturbations on regular black hole backgrounds in a variety of models.

We describe the implementation of a search for gravitational waves from compact binary coalescences in LIGO and Virgo data. This all-sky, all-time, multidetector search for binary coalescence has been used to search data taken in recent LIGO and Virgo runs. The search is built around a matched filter analysis of the data, augmented by numerous signal consistency tests designed to distinguish artifacts of non-Gaussian detector noise from potential detections. We demonstrate the search performance using Gaussian noise and data from the fifth LIGO science run and demonstrate that the signal consistency tests are capable of mitigating the effect of non-Gaussian noise and providing a sensitivity comparable to that achieved in Gaussian noise.

The Affleck-Dine mechanism, which is one of the most attractive candidates for baryogenesis in supersymmetric theories, often predicts the existence of baryonic $Q$-balls in the early universe. In this scenario, there is a possibility to explain the observed baryon-to-dark-matter ratio because $Q$-balls decay into supersymmetric particles as well as quarks. If the gravitino mass is small compared to the typical interaction energy, the longitudinal component of the gravitino behaves like the massless goldstino. We numerically calculate the goldstino production rates from $Q$-balls in the leading semiclassical approximation without using the large-radius limit or effective coupling. We also calculate the quark production rates from $Q$-balls in the Yukawa theory with a massive fermion. In deriving the decay rate we also take into account the scalar field configuration of the $Q$-ball. These results are applied to a realistic model in the gauge-mediated supersymmetry breaking and yield the branching ratio of the $Q$-ball decay into the gravitino. We obtain a branching ratio much smaller than the one estimated in the previous analysis.

Gravitational particle production naturally occurs during the transition from the inflationary phase to the noninflationary phase. If the particles are stable and very weakly interacting, they are natural nonthermal dark matter candidates. We show that such nonthermal dark matter particles can produce local non-Gaussianities large enough to be observed by ongoing and near future experiments without being in conflict with the existing isocurvature bounds. Of particular interest is the fact that these particles can be observable through local non-Gaussianities even when they form a very small fraction of the total dark matter content.

A very interesting generalization of the running vacuum energy density has been recently advanced [S. Basilakos, D. Polarski, and J. Sola, Phys. Rev. D 86, 043010 (2012)]. The Friedmann equation of this model looks pretty much similar to that of a homogeneous and isotropic universe filled with an holographic Ricci dark energy (HRDE) component. Despite the analogy between these two models, it turns out that one of them, generalization of the running vacuum energy, is singularity-free in the future while the other, HRDE, is not. Indeed, a universe filled with an HRDE component can hit, for example, a big rip singularity. We clarify this issue by solving analytically the Friedmann equation for both models and analyzing the role played by the local conservation of the energy density of the different components when filling the universe. In addition, not everything is bad news about the HRDE. In fact, we point out that in some particular cases the HRDE, when endowed with a negative cosmological constant and in the absence of an explicit dark matter component, can mimic dark matter and explain the late-time cosmic acceleration of the universe through an asymptotically de Sitter universe.

Ultra slow-roll inflation has recently been used to challenge the non-Gaussianity consistency relation. We show that this inflationary scenario belongs to a one-parameter class of models, and we study its properties and observational predictions. We demonstrate that the power spectrum remains scale invariant and that the bispectrum is of the local type with $f_{\mathrm{NL}}=5(3-n_{\mathrm{s}})/4$, which indeed represents a modification of the consistency relation. However, we also show that the system is unstable and suffers from many physical problems among which is the difficulty in correctly WMAP normalizing the model. We conclude that ultra slow-roll inflation remains a very peculiar case, the physical relevance of which is probably not sufficient to call into question the validity of the consistency relation.