The rotational energy of a black hole can be extracted via the Blandford-Znajek mechanism and numerical simulations suggest a strong dependence of the power of the produced jet on the black-hole spin. A recent study has found no evidence for a correlation between the spin and the power of steady jets. If the measurements of the spin and of the jet power are correct, it leads one to conclude that steady jets are not powered by the black-hole spin. In this paper, I explore another possibility: I assume that steady jets are powered by the spin and I check if current observations can be explained if astrophysical black hole candidates are not the Kerr black hole predicted by general relativity. It turns out that this scenario might indeed be possible. While such a possibility is surely quite speculative, it is definitively intriguing and can be seriously tested when future, more accurate measurements will be available.

It has become common understanding that the recession of galaxies and the corresponding redshift of light received from them can only be explained by an expansion of the space between them and us. In this paper, for the presently favored case of a universe without spatial curvature, it is shown that this interpretation is restricted to comoving coordinates. It is proven by construction that within the framework of general relativity other coordinates exist in relation to which these phenomena can be explained by a motion of the cosmic substrate across space, caused by an explosionlike big bang or by inflation preceding an almost big bang. At the place of an observer, this motion occurs without any spatial expansion. It is shown that in these “explosion coordinates” the usual redshift comes about by a Doppler shift and a subsequent gravitational shift. Making use of this interpretation, it can easily be understood why in comoving coordinates light rays of short spatial extension expand and thus constitute an exemption from the rule that small objects up to the size of the solar system or even galaxies do not participate in the expansion of the universe. It is also discussed how the two interpretations can be reconciled with each other.

In gravitational-wave interferometers, test masses are suspended on thin fibers which experience considerable tension stress. Sudden microscopic stress release in a suspension fiber, which I call a “creep event,” would excite motion of the test mass that would be coupled to the interferometer’s readout. The random test-mass motion due to a time sequence of creep events is referred to as “creep noise.” In this paper I present an elastodynamic calculation for the test-mass motion due to a creep event. I show that within a simple suspension model, the main coupling to the optical readout occurs via a combination of a “dc” horizontal displacement of the test mass and excitation of the violin and pendulum modes, and not, as was thought previously, via lengthening of the fiber. When the creep events occur sufficiently frequently and their statistics is time independent, the creep noise can be well approximated by a stationary Gaussian random process. I derive the functional form of the creep noise spectral density in this limit, with the restrictive assumption that the creep events are statistically independent from each other.

A new and novel idea for a predictive neutrino mass matrix is presented, using the non-Abelian discrete symmetry $A_4$ and the seesaw mechanism with only two heavy neutral fermion singlets. Given the components of the one necessarily massless neutrino eigenstate, the other two massive states are automatically generated. A realistic example is discussed with predictions of a normal hierarchy of neutrino masses and maximal $CP$ violation.

The antisymmetry requirement of rishon bound state wave functions suggests a new rishon quantum number called $M$ spin. From $M$ spin conservation and the Nussinov-Weingarten-Witten theorem we predict the existence of a stable pseudoscalar dirishonic meson $\zeta$ that is lighter than the lightest neutrino. Its mass is estimated as $m_{\zeta }={10}^{-9}\mathrm{eV}$. This particle could make up the major part of cold dark matter in the Universe.

In this paper we first calculate the form factors of $B\to (\pi ,K)$ and $B_s\to K$ transitions by employing the perturbative QCD (pQCD) factorization approach with the inclusion of the next-to-leading-order (NLO) corrections, and then we calculate the branching ratios of the corresponding semileptonic decays $B/B_s\to (\pi ,K)(l^{+}{l}^{-},l\nu ,\nu \overline{\nu })$ (here $l$ denotes $e$, $\mu$, and $\tau$). Based on the numerical calculations and phenomenological analysis, we find the following results: (a) For $B\to (\pi ,K)$ and $B_s\to K$ transition form factors $F_{0,+,\mathrm{T}}(q^2)$, the NLO pQCD predictions for the values of $F_{0,+,\mathrm{T}}(0)$ and their $q^2$ dependence agree well with those obtained from other methods; (b) for ${\overline{B}}^0\to {\pi }^{+}{l}^{-}{\overline{\nu }}_l$, ${\overline{K}}^0{l}^{+}{l}^{-}$ and $B^{-}\to {\pi }^0{l}^{-}{\overline{\nu }}_l$, $K^{-}{l}^{+}{l}^{-}$ decay modes, the NLO pQCD predictions for their branching ratios agree very well with the measured values; (c) by comparing the pQCD predictions for $\mathrm{Br}({\overline{B}}^0\to {\pi }^{+}{l}^{-}{\overline{\nu }}_l)$ with the measured decay rate, we extract out the magnitude of $V_{ub}$: $|V_{ub}|=({3.80}_{-0.60}^{+0.66}(\mathrm{theor})\pm 0.13)\times {10}^{-3}$; (d) we also define several ratios of the branching ratios, $R_{\nu }$, $R_C$ and $R_{N1,N2,N3}$, and present the corresponding pQCD predictions, which will be tested by LHCb and the forthcoming Super-B experiments.

The recent observations of muon charge ratio up to about 10 TeV and of atmospheric neutrinos up to energies of about 400 TeV have triggered a renewed interest into the high-energy interaction models and cosmic-ray primary composition. A reviewed calculation of lepton spectra produced in cosmic-ray-induced extensive air showers is carried out with a primary cosmic-ray spectrum that fits the latest direct measurements below the knee. In order to achieve this, we used a full Monte Carlo method to derive the inclusive differential spectra (yields) of muons, muon neutrinos and electron neutrinos at the surface for energies between 80 GeV and hundreds of PeV. Using these results, the differential flux and the flavor ratios of leptons were calculated. The air shower simulator CORSIKA 6.990 was used for showering and propagation of the secondary particles through the atmosphere, employing the established high-energy hadronic interaction models SIBYLL 2.1, QGSJet-01 and QGSJet-II-03. We show that the performance of the interaction models makes it possible to predict the spectra within experimental uncertainties, while SIBYLL generally yields a higher flux at the surface than the QGSJet models. The calculation of the flavor and charge ratios has lead to inconsistent results, mainly influenced by the different representations of the $K/\pi$ ratio within the models. The influence of the knee of cosmic rays is reflected in the secondary spectra at energies between 100 and 200 TeV. Furthermore, we could quantify systematic uncertainties of atmospheric muon and neutrino fluxes, associated to the models of the primary cosmic-ray spectrum and the interaction models. For most recent parametrizations of the cosmic-ray primary spectrum, atmospheric muons can be determined with an uncertainty smaller than $\genfrac{}{}{0ex}{}{+15}{-13}\%$ of the average flux. Uncertainties of the muon and electron neutrino fluxes can be calculated within an average error of $\genfrac{}{}{0ex}{}{+32}{-22}\%$ and $\genfrac{}{}{0ex}{}{+25}{-19}\%$, respectively.

We propose formulas for computing the phase space integrals of $1\to 3$ and $1\to 4$ processes with massive particles in final states. As an application of these formulas, we study the final state mass effects in some interesting phenomenological cases, giving fully integrated analytic results for the corresponding phase spaces. We consider also the $B_s-{\overline{B}}_s$ process at next-to-next-to-leading order and calculate one of the most complicated master integrals, which contributes to the $\Delta {\Gamma }_{B_s}$ at $O({\alpha }_s^2)$.

The observation of a new boson of mass $\sim 125\mathrm{GeV}$ at the CERN LHC may finally have revealed the existence of a Higgs boson. Now we have the opportunity to scrutinize its properties, determining its quantum numbers and couplings to the standard model particles, in order to confirm or not its discovery. We show that by the end of the 8 TeV run, combining the entire data sets of ATLAS and CMS, it will be possible to discriminate between the following discovery alternatives: a narrow scalar $J^P=0^{+}$ or a tensor $J^P=2^{+}$ particle with minimal couplings to photons, at a $5\sigma$ statistical confidence level at least, using only diphoton events. Our results are based on the calculation of a center-edge asymmetry measure of the reconstructed sPlot scattering polar angle of the diphotons. The results based on asymmetries are shown to be robust against systematic uncertainties on signal and backgrounds normalizations with comparable discrimination power to a log likelihood ratio statistic.

We argue that $\Delta L=2$ neutrino spin flavor precession, induced by the primordial magnetic fields, could have a significant impact on the leptogenesis process that accounts for the baryon asymmetry of the Universe. Although the extragalactic magnetic field is extremely weak at the present time (about ${10}^{-9}\mathrm{Gauss}$), the primordial magnetic field at the electroweak scale could be quite strong (of order ${10}^{17}\mathrm{Gauss}$). Therefore, at this scale, the effects of the spin flavor precession are not negligible. We show that the lepton asymmetry may be reduced by 50% due to the spin flavor precession. In addition, the leptogenesis will have different features from the standard scenario of leptogenesis, where the lepton asymmetry continues to oscillate even after the electroweak phase transition.

The fermion-sign problem at finite density is a persisting challenge for Monte Carlo simulations. Theories that do not have a sign problem can provide valuable guidance and insight for physically more relevant ones that do. Replacing the gauge group SU(3) of QCD by the exceptional group ${\mathrm{G}}_2$, for example, leads to such a theory. It has mesons as well as bosonic and fermionic baryons, and shares many features with QCD. This makes the ${\mathrm{G}}_2$ gauge theory ideally suited to study general properties of dense, strongly interacting matter, including baryonic and nuclear Fermi pressure effects. Here we present the first-ever results from lattice simulations of ${\mathrm{G}}_2$ QCD with dynamical fermions, providing a first explorative look at the phase diagram of this QCD-like theory at finite temperature and baryon chemical potential.

Recently, a modified theory of gravity was presented, which consists of the superposition of the metric Einstein-Hilbert Lagrangian with an $f(\mathcal{R})$ term constructed à la Palatini. The theory possesses extremely interesting features such as predicting the existence of a long-range scalar field, that explains the late-time cosmic acceleration and passes the local tests, even in the presence of a light scalar field. In this brief report, we consider the possibility that wormholes are supported by this hybrid metric-Palatini gravitational theory. We present here the general conditions for wormhole solutions according to the null energy conditions at the throat and find specific examples. In the first solution, we specify the redshift function, the scalar field and choose the potential that simplifies the modified Klein-Gordon equation. This solution is not asymptotically flat and needs to be matched to a vacuum solution. In the second example, by adequately specifying the metric functions and choosing the scalar field, we find an asymptotically flat spacetime.

We present a formulation of naturalness made in the framework of Bayesian statistics, which unravels the conceptual problems related to previous approaches. Among other things, the relative interpretation of the measure of naturalness turns out to be unambiguously established by Jeffreys’ scale. Also, the usual sensitivity formulation (the so-called Barbieri-Giudice measure) appears to be embedded in our formulation under an extended form. We derive the general sensitivity formula applicable to an arbitrary number of observables. Several consequences and developments are further discussed. As a final illustration, we work out the map of combined fine-tuning associated with the gauge hierarchy problem and neutralino dark matter in a classic supersymmetric model.

We find the first nonlinear correction to the field produced by a static charge at rest in a background constant magnetic field. It is quadratic in the charge and purely magnetic. The third-rank polarization tensor—the nonlinear response function—is written within the local approximation of the effective action in an otherwise model- and approximation-independent way within any $P$-invariant nonlinear electrodynamics, QED included.

The interest of part of the quantum-gravity community in the possibility of Planck-scale-deformed Lorentz symmetry is also fueled by the opportunities for testing the relevant scenarios with analyses, from a signal-propagation perspective, of observations of bursts of particles from cosmological distances. In this respect the fact that so far the implications of deformed Lorentz symmetry have been investigated only for flat (Minkowskian) spacetimes represents a very significant limitation, since for propagation over cosmological distances the curvature/expansion of spacetime is evidently tangible. We here provide a significant step toward filling this gap by exhibiting an explicit example of Planck-scale-deformed relativistic symmetries of a spacetime with constant rate of expansion (de Sitterian). Technically, we obtain the first ever example of a relativistic theory of worldlines of particles with 3 nontrivial relativistic invariants: a large speed scale (“speed-of-light scale”), a large distance scale (inverse of the “expansion-rate scale”), and a large momentum scale (“Planck scale”). We address some of the challenges that had obstructed success for previous attempts by exploiting the recent understanding of the connection between deformed Lorentz symmetry and relativity of spacetime locality. We also offer a preliminary analysis of the differences between the scenario we here propose and the most studied scenario for broken (rather than deformed) Lorentz symmetry in expanding spacetimes.

The geodesic deviation equation, describing the relative accelerations of nearby particles, and the Raychaudhury equation, giving the evolution of the kinematical quantities associated with deformations (expansion, shear, and rotation) are considered in the framework of modified theories of gravity with an arbitrary curvature-matter coupling, by taking into account the effects of the extra force. As a physical application of the geodesic deviation equation, the modifications of the tidal forces due to the supplementary curvature-matter coupling are obtained in the weak-field approximation. The tidal motion of test particles is directly influenced not only by the gradient of the extra force, which is basically determined by the gradient of the Ricci scalar, but also by an explicit coupling between the velocity and the Riemann curvature tensor. As a specific example, the expression of the Roche limit (the orbital distance at which a satellite will begin to be tidally torn apart by the body it is orbiting) is also obtained for this class of models.

The Dirac Lagrangian is minimally coupled to the most general $R+T+T^2$-type Lagrangian in ($1+2$)-dimensions. The field equations are obtained from the total Lagrangian by a variational principle. The space-time torsion is calculated algebraically in terms of the Dirac condensate plus coupling coefficients. A family of circularly symmetric rotating exact solutions which is asymptotically three-dimensional anti–de Sitter is obtained. Finally, Banados-Teitelboim-Zanelli-like solutions are discussed.

Theoretical studies in gravitational wave astronomy have mostly focused on the information that can be extracted from individual detections, such as the mass of a binary system and its location in space. Here we consider how the information from multiple detections can be used to constrain astrophysical population models. This seemingly simple problem is made challenging by the high dimensionality and high degree of correlation in the parameter spaces that describe the signals, and by the complexity of the astrophysical models, which can also depend on a large number of parameters, some of which might not be directly constrained by the observations. We present a method for constraining population models using a hierarchical Bayesian modeling approach which simultaneously infers the source parameters and population model and provides the joint probability distributions for both. We illustrate this approach by considering the constraints that can be placed on population models for galactic white dwarf binaries using a future space-based gravitational wave detector. We find that a mission that is able to resolve $\sim 5000$ of the shortest period binaries will be able to constrain the population model parameters, including the chirp mass distribution and a characteristic galaxy disk radius to within a few percent. This compares favorably to existing bounds, where electromagnetic observations of stars in the galaxy constrain disk radii to within 20%.

We perform a Fisher matrix analysis to forecast the capability of ongoing and future Sunyaev-Zeldovich cluster surveys in constraining the deviations from Gaussian distribution of primordial density perturbations. We use the constraining power of the cluster number counts and clustering properties to forecast limits on the $f_{\mathrm{NL}}$ parameter. The primordial non-Gaussianity (NG) effects on the mass function and halo bias are considered. We adopt self-calibration for the mass-observable scaling relation and evaluate constraints for the South Pole Telescope, Planck, CCAT-like, South Pole Telescope polarization survey, and Atacama Cosmology Telescope polarization survey. We show that the scale dependence of the halo bias induced by the local NG provides strong constraints on $f_{\mathrm{NL}}$, while the results from number count are two orders of magnitude worse. When combining information from number counts and the power spectrum, the Planck cluster catalog provides the tightest constraint with ${\sigma }_{f_{\mathrm{NL}}}=7$ (68% C.L.) even for relatively conservative assumptions on the expected cluster yields and systematics. This value is a factor of 2 smaller than the $1\sigma$ error as measured by WMAP cosmic microwave background measurements and comparable to what is expected from Planck. We find that the results are mildly sensitive to the mass threshold of the surveys but strongly depend on the survey coverage; a full-sky survey like Planck is more favorable because it can probe longer wavelength modes that are most sensitive to NG effects. In addition, the constraints are largely insensitive to priors on nuisance parameters as they are mainly driven by the power spectrum probe, which has a mild dependence on the mass-observable relations.

Recently, studies of the gravitational collapse of a scalar field within spherically symmetric anti–de Sitter (AdS) spacetimes presented by Bizon and Rostroworoski [Phys. Rev. Lett. 107, 031102 (2011)], Jalmuzna et al. [Phys. Rev. D 84, 085021 (2011).] showed an instability of pure AdS to black hole formation. In particular, the work showed that arbitrarily small initial configurations of a scalar field evolved through some number of reflections off the AdS boundary until a black hole forms. We consider this same system, extended to include a complex scalar field, and reproduce this phenomena. We present tests of our numerical code that demonstrate convergence and consistency. We study the properties of the evolution as the scalar pulse becomes more compact by examining the asymptotic behavior of the scalar field, an observable in the corresponding boundary conformal field theory. We demonstrate that such black hole formation occurs even when one places a reflecting boundary at finite radius, indicating that the sharpening is a property of gravity in a bounded domain and not of AdS itself. We examine how the initial energy is transferred to higher frequencies—which leads to black hole formation—and uncover interesting features of this transfer.