The Newman-Janis algorithm has been widely used to construct rotating black hole solutions from nonrotating counterparts. While this algorithm was developed within general relativity (GR), it has more recently been applied to nonrotating solutions in modified gravity theories. We find that the application of the Newman-Janis algorithm to an arbitrary non-GR spherically symmetric solution introduces pathologies in the resulting axially symmetric metric. This then establishes that, in general, the Newman-Janis algorithm should not be used to construct rotating black hole solutions outside of General Relativity.

We constrain the neutrino properties in $f(R)$ gravity using the latest observations from cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements. We first constrain separately the total mass of neutrinos $\sum _{}^{}{m}_{\nu }$ and the effective number of neutrino species $N_{\mathrm{eff}}$. Then we constrain $N_{\mathrm{eff}}$ and $\sum _{}^{}{m}_{\nu }$ simultaneously. We find $\sum _{}^{}{m}_{\nu }<0.462\mathrm{eV}$ at a 95% confidence level for the combination of Planck CMB data, WMAP CMB polarization data, BAO data, and high-$l$ data from the Atacama Cosmology Telescope and the South Pole Telescope. We also find $N_{\mathrm{eff}}={3.32}_{-0.51}^{+0.54}$ at a 95% confidence level for the same data set. When constraining $N_{\mathrm{eff}}$ and $\sum _{}^{}{m}_{\nu }$ simultaneously, we find $N_{\mathrm{eff}}={3.58}_{-0.69}^{+0.72}$ and $\sum _{}^{}{m}_{\nu }<0.860\mathrm{eV}$ at a 95% confidence level, respectively.

We show that the typical 3-3-1 models are only self-consistent if they contain interactions that explicitly violate the lepton number. The 3-3-1 model with right-handed neutrinos can by itself work as an economical 3-3-1 model as a natural recognition of the above criteria, while it also produces an inert scalar triplet ($\eta$) responsible for dark matter. This is ensured by a $Z_2$ symmetry (assigned so that only $\eta$ is odd while all other multiplets which perform the economical 3-3-1 model are even), which is not broken by the vacuum. The minimal 3-3-1 model can provide dark matter by a similar realization. Taking the former into account, we show that the dark matter candidate ($H_{\eta }$) contained in $\eta$ transforms as a singlet in the effective limit under the standard model symmetry and is naturally heavy. The $H_{\eta }$ relic density and direct detection cross section will have the correct values when the mass of $H_{\eta }$ is in TeV range, as expected. The model predicts the $H_{\eta }$ mass $m_{H_{\eta }}={\lambda }_5\times 2\mathrm{TeV}$ and the $H_{\eta }$-nucleon scattering cross section ${\sigma }_{H_{\eta }-N}=1.56\times {10}^{-44}{\mathrm{cm}}^2$, provided that the new neutral Higgs boson is much heavier than the dark matter.

Using the pre-LHC and LHC data for $\pi p$ and $pp$ diffractive collisions, we study the ultrahigh-energy asymptotic regime in the framework of the black disk picture. The black disk picture, being constrained by the $s$-channel unitarity condition and the $t$-channel analyticity, gives rather definite predictions for diffractive processes increasing with the energy. To deal with the data, we consider the Dakhno-Nikonov eikonal model, which predicts a growth of the ${ln}^{2}s$ type for total and elastic cross sections and ($\tau ={\mathbf{q}}_{\perp }^2{ln}^{2}s$) scaling for diffractive scattering and diffractive dissociation of hadrons. According to the calculations, ultrahigh-energy asymptotic characteristics of diffractive and total cross sections are universal, and this results in the asymptotic equality of cross sections for all types of hadrons. We estimate the energy scale of the asymptotics in different processes. The manifestation of the asymptotic regime in hadron fragmentation reactions is discussed.

We consider the possible production of the Higgs boson in association with a top-quark pair and its subsequent decay into a tau-lepton pair or a $W$-boson pair. This process can give rise to many signatures of the Higgs boson. These signatures can have electrons, muons, tau jets, bottom jets and/or light flavor jets. We analyze the viability of some of these signatures. We will look at those signatures where the background is minimal. In particular, we explore the viability of the signatures “isolated 4 electron/muon” and “isolated $3\mathrm{\text{electron}}/\mathrm{\text{muon}}+\mathrm{\text{a jet}}$.” The jet can be due to a light flavor quark/gluon, a bottom quark, or a tau lepton. Of all these signatures, we find that “isolated $3\mathrm{\text{electron}}/\mathrm{\text{muon}}+\mathrm{\text{a tau jet}}$,” with an extra bottom jet, can be an excellent signature of this mode of the Higgs boson production. We show that this signature may be visible within a year, once the Large Hadron Collider (LHC) restarts. Some of the other signatures would also be observable after the Large Hadron Collider accumulates sufficient luminosity.

We present a measurement of the charge-parity ($CP$) violating parameters in $B^0\to {\pi }^{+}{\pi }^{-}$ decays. The results are obtained from the final data sample containing $772\times {10}^6$ $B\overline{B}$ pairs collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We obtain the $CP$ violation parameters $${\mathcal{A}}_{CP}(B^0\to {\pi }^{+}{\pi }^{-})=+0.33\pm 0.06(\mathrm{stat})\pm 0.03(\mathrm{syst}),{\mathcal{S}}_{CP}(B^0\to {\pi }^{+}{\pi }^{-})=-0.64\pm 0.08(\mathrm{stat})\pm 0.03(\mathrm{syst}),$$where ${\mathcal{A}}_{CP}$ and ${\mathcal{S}}_{CP}$ represent the direct and mixing-induced $CP$ asymmetries in $B^0\to {\pi }^{+}{\pi }^{-}$ decays, respectively. Using an isospin analysis including results from other Belle measurements, we find $23.8°<{\varphi }_2<66.8°$ is disfavored at the $1\sigma$ level, where ${\varphi }_2$ is one of the three interior angles of the Cabibbo-Kobayashi-Maskawa unitarity triangle related to $B_{u,d}$ decays.

The dilaton-limit fixed point and the scaling properties of hadrons in the close vicinity of the fixed point in dense baryonic matter uncovered in hidden local symmetry implemented with spontaneously broken scale symmetry are shown to reveal a surprisingly intricate interplay, hitherto unsuspected, between the origin of the bulk of proton mass and the renormalization-group flow of the $\omega$-nuclear interactions. This rends theoretical support to the previous (phenomenologically) observed correlation between the dropping nucleon mass and the behavior of the $\omega$-nuclear interactions in dense matter described in terms of half Skyrmions that appear at a density denoted $n_{1/2}$ in Skyrmion crystals. The role of the $\omega$-meson degree of freedom in the source for nucleon mass observed in this paper is highly reminiscent of its important role in the Skyrmion description of nucleon mass in hidden local symmetric theory. One of the most notable novel results found in this paper is that the nucleon mass in a dense baryonic medium undergoes a drop roughly linear in density up to a density (denoted $\tilde{n}$) slightly above the nuclear matter density ($n_0$) and then stays more or less constant up to the dilaton-limit fixed point. The possibility that we entertain is that $\tilde{n}$ coincides with or is at least close to $n_{1/2}$. We note that this feature can be economically captured by the parity-doublet model for nucleons with the chiral-invariant mass $m_0\sim (0.7–0.8)m_N$. It is found in one-loop renormalization-group analysis with the Lagrangian adopted that, while the $\rho \mathrm{\text{−}}NN$ coupling “runs” in density, the $\omega \mathrm{\text{−}}NN$ coupling does not scale: It will scale at two-loop or higher-loop order, but at a slower pace, so it is more appropriate to say it “walks” rather than runs. The former implies a drastic change in the nuclear tensor forces, affecting, among others, the nuclear symmetry energy and the latter generating the stiffness of the equation of state at density higher than that of normal nuclear matter.

Hybrid metric-Palatini gravity is a recent and novel approach to modified theories of gravity, which consists of adding to the metric Einstein-Hilbert Lagrangian an $f(\mathcal{R})$ term constructed à la Palatini. It was shown that the theory passes local tests even if the scalar field is very light, and thus implies the existence of a long-range scalar field, which is able to modify the dynamics in galactic and cosmological scales, but leaves the Solar System unaffected. In this work, motivated by the possibility that the Universe may have started out in an asymptotically Einstein static state in the inflationary universe context, we analyze the stability of the Einstein static universe by considering linear perturbations in the respective dynamically equivalent scalar-tensor representation of hybrid metric-Palatini gravity. Considering linear homogeneous and inhomogeneous perturbations, the stability regions of the Einstein static universe are parametrized by the first and second derivatives of the scalar potential, and it is explicitly shown that a large class of stable solutions exists in the respective parameter space, in the context of hybrid metric-Palatini gravity.

We study here the r-modes in the Cowling approximation of a slowly rotating and magnetized neutron star with a poloidal magnetic field, where we neglect any deformations of the spherical symmetry of the star. We were able to quantify the influence of the magnetic field in both the oscillation frequency ${\sigma }_r$ of the r-modes and the growth time $t_{gw}$ of the gravitational radiation emission. We conclude that magnetic fields of the order ${10}^{15}\mathrm{G}$ at the center of the star are necessary to produce any changes. Our results for ${\sigma }_r$ show a decrease of up to $\sim 5\%$ in the frequency with increasing magnetic field, with a $B^2$ dependence for rotation rates $\Omega /{\Omega }_K\gtrsim 0.07$ and $B^4$ for $\Omega /{\Omega }_K\lesssim 0.07$. (These results should be trusted only within the slow rotation approximation, and we kept $\Omega /{\Omega }_K<0.3$.) For $t_{gw}$, we find that it is approximately 30% smaller than previous Newtonian results for nonmagnetized stars, which would mean a faster growth of the emission of gravitational radiation. The effect of the magnetic field in $t_{gw}$ causes a nonmonotonic effect that first slightly increases $t_{gw}$ and then decreases it further by another $\sim 5\%$. (The value of the magnetic field for which $t_{gw}$ starts to decrease depends on the rotational frequency, but it is generally around ${10}^{15}\mathrm{G}$.) Future work should be dedicated to the study of the effect of viscosity in the presence of magnetic fields, in order to establish the magnetic correction to the instability window.

We study the stability of a rotating (Kerr) black hole in viable $f(R)$ gravity. The linearized-Ricci scalar equation shows a superradiant instability, leading to the instability of the Kerr black hole in $f(R)$ gravity.

We assume cold dark matter to possess a small bulk-viscous pressure which typically attenuates the growth of inhomogeneities. Explicit calculations, based on Eckart’s theory of dissipative processes, reveal that for viscous cold dark matter the usual Newtonian approximation for perturbation scales smaller than the Hubble scale is no longer valid. We advocate the use of a neo-Newtonian approach which consistently incorporates pressure effects into the fluid dynamics and correctly reproduces the general relativistic dynamics. This result is of interest for numerical simulations of nonlinear structure formation involving nonstandard dark-matter fluids. We obtain upper limits on the magnitude of the viscous pressure by requiring that relevant perturbation amplitudes should grow sufficiently to enter the nonlinear stage.

The window is found in the space of the free parameters of the theory of viscoelastic matter for which the Friedmann singularity is stable. By stability we mean that in the presence of the shear stresses, a generic solution of the equations of relativistic gravity possessing an isotropic singularity exists.

Cosmological tests to distinguish between dark energy (DE) and modifications to gravity are a promising route to obtain clues on the origin of cosmic acceleration. We study here the robustness of these tests to the presence of DE density, velocity, and anisotropic stress perturbations. We find that the dispersion in the growth index parameter remains small enough to distinguish between extreme cases of DE models and some commonly used modified gravity models. The sign of the slope parameter for a redshift-dependent growth index was found to be inconsistent as an additional test in extreme cases of DE models with perturbations. Next, we studied the effect of DE perturbations on the modified growth (MG) parameters that enter the perturbed Einstein equations. We find that while the dark energy perturbations affect the MG parameters, the deviations remain smaller than those due to modified gravity models. Additionally, the deviations due to DE perturbations with a nonzero effective sound speed occur at scale ranges that are completely different than those due to some modified gravity models such as the $f(R)$ models. In the case of modified gravity models with zero anisotropic stress at late times, the simultaneous determination of the effective dark energy equation of state and the MG parameters can provide the distinction between these models and DE. The growth index test was found to be the most robust to these perturbations. The scale dependence of the MG parameters in some cases of modified gravity constitutes a clear-cut discriminant regardless of any DE perturbations. In summary, we find that the currently proposed cosmological tests to distinguish between DE and modified gravity are robust to DE perturbations even for extreme cases. This is certainly the case even for DE models with equations of state of DE that fall well outside of current cosmological constraints.

We study regular and asymptotically flat phantom black holes as gravitational lenses. We obtain the deflection angle in both the weak and the strong deflection limits, from which we calculate the positions, magnifications, and time delays of the images. We compare our results with those corresponding to the Schwarzschild solution and to the vacuum Brans-Dicke black hole.

We present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic center region, performed on two years of data from LIGO’s fifth science run from two LIGO detectors. The search uses a semicoherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequency-dependent range of first-order spindown values down to $-7.86\times {10}^{-8}\mathrm{Hz}/\mathrm{s}$ at the highest frequency. No gravitational waves were detected. The 90% confidence upper limits on the gravitational wave amplitude of sources at the Galactic center are $\sim 3.35\times {10}^{-25}$ for frequencies near 150 Hz. These upper limits are the most constraining to date for a large-parameter-space search for continuous gravitational wave signals.

The lack of evidence for superparticles at the CERN LHC, along with the rather high value of the Higgs boson mass, has sharpened the perception that what remains of supersymmetric model parameter space suffers a high degree of electroweak fine-tuning (EWFT). We compare three different measures of fine-tuning in supersymmetric models. First, ${\Delta }_{HS}$ measures a subset of terms containing large log contributions to $m_Z$ (and $m_h$) that are inevitable in models defined at scales much higher than the electroweak scale. Second, the traditional ${\Delta }_{BG}$ measures fractional variation in $m_Z$ against fractional variation of model parameters and allows for correlations among high scale parameters which are not included in ${\Delta }_{HS}$. Third, the model-independent ${\Delta }_{EW}$ measures how naturally a model can generate the measured value of $m_Z=91.2\mathrm{GeV}$ (or $m_h$) in terms of weak scale parameters alone. We hypothesize an overarching ultimate theory (UTH) wherein the high scale soft terms are all correlated. The UTH might be contained within the more general effective supersymmetry theories which are popular in the literature. In the case of ${\Delta }_{HS}$, EWFT can be grossly overestimated by neglecting additional nonindependent terms which lead to large cancellations. In the case of ${\Delta }_{BG}$, EWFT can be overestimated by applying the measure to the effective theories instead of to the UTH. The measure ${\Delta }_{EW}$ allows for the possibility of parameter correlations which should be present in the UTH and, since it is model independent, provides the same value of EWFT for the effective theories as should occur for the UTH. We find that the well-known minimal supergravity model/constrained minimal supersymmetric model is fine-tuned under all three measures so that it is unlikely to contain the UTH. The nonuniversal Higgs model NUHM2 appears fine-tuned with ${\Delta }_{HS,BG}\gtrsim {10}^3$. But since ${\Delta }_{EW}$ can be as small as 7 (corresponding to 14% fine-tuning), it may contain the UTH for parameter ranges which allow for low true EWFT.

The spectrum of a system with multiple channels composed of two hadrons with nonzero total momentum is determined in a finite cubic volume with periodic boundary conditions using effective field theory methods. The results presented are accurate up to exponentially suppressed corrections in the volume due to the finite range of hadronic interactions. The formalism allows one to determine the phase shifts and mixing parameters of $\pi \pi -KK$ isosinglet coupled channels directly from lattice quantum chromodynamics. We show that the extension to more than two channels is straightforward and present the result for three channels. From the energy quantization condition, the volume dependence of electroweak matrix elements of two-hadron processes is extracted. In the nonrelativistic case, we pay close attention to processes that mix the ${}^{1}S_0-{}^{3}S_1$ two-nucleon states, e.g. proton-proton fusion ($pp\to d+e^{+}+{\nu }_e$), and show how to determine the transition amplitude of such processes directly from lattice QCD.

We investigate the chiral properties of $\mathrm{SU}(2{)}_{\mathrm{C}}$ gauge theory with six flavors, i.e., six light Dirac fermions in the fundamental representations by lattice simulation, and point out that the spontaneous breakdown of chiral symmetry does not occur in this system. The quark mass dependence of the mesonic spectrum provides evidence for such a possibility. The decay constant tends to be increased by the finite size effect, which is opposite to the behavior predicted by chiral perturbation theory and indicates that the long distance dynamics in the six-flavor theory could be different from the theory with chiral symmetry breaking. The subtracted chiral condensate, whose utility is demonstrated by the simulation of two-flavor theory, is shown to vanish in the chiral limit within the precision of available data.

We report on the extraction of an excited spectrum of isoscalar mesons using lattice QCD. Calculations on several lattice volumes are performed with a range of light quark masses corresponding to pion masses down to $\sim 400\mathrm{MeV}$. The distillation method enables us to evaluate the required disconnected contributions with high statistical precision for a large number of meson interpolating fields. We find relatively little mixing between $\frac{1}{\sqrt{2}}(u\overline{u}+d\overline{d})$ and $s\overline{s}$ in most $J^{PC}$ channels; one notable exception is the pseudoscalar sector where the approximate $SU(3{)}_F$ octet, singlet structure of the $\eta$, ${\eta }^{\prime }$ is reproduced. We extract exotic $J^{PC}$ states, identified as hybrid mesons in which an excited gluonic field is coupled to a color-octet $q\overline{q}$ pair, along with nonexotic hybrid mesons embedded in a $q\overline{q}$-like spectrum.

In the exploration of viable models of dynamical electroweak symmetry breaking, it is essential to locate the lower end of the conformal window and know the mass anomalous dimensions there for a variety of gauge theories. We calculate, with the Schrödinger functional scheme, the running coupling constant and the mass anomalous dimension of SU(2) gauge theory with six massless Dirac fermions in the fundamental representation. The calculations are performed on $6^4–{24}^4$ lattices over a wide range of lattice bare couplings to take the continuum limit. The discretization errors for both quantities are removed perturbatively. We find that the running slows down and comes to a stop at $0.06\lesssim 1/g^2\lesssim 0.15$ where the mass anomalous dimension is estimated to be $0.26\lesssim {\gamma }_m^{*}\lesssim 0.74$.