It has been argued that, starting with a slightly subextremal Kerr black hole instead of an extremal one, it is possible to overspin a black hole past the extremal limit and turn it into a naked singularity by sending test bodies, if one neglects radiative and self-force effects. In this work we show that (i) an extremal Kerr black hole cannot be overspun as a result of the interaction with massless integer-spin test fields (scalar, electromagnetic, or gravitational), (ii) overspinning can be achieved if we start with a nearly extremal black hole instead, and (iii) for the scalar field, the argument applies to more general black holes, and also allows use of a more general field configuration. Our analysis also neglects radiative and self-force effects.

The Kerr metric is one of the most important solutions to Einstein’s field equations describing the gravitational field outside a rotating black hole. We thoroughly analyze the curvature scalar invariants to study the Kerr spacetime by examining and visualizing their covariant gradient fields. We discover that the part of the Kerr geometry outside the black hole horizon changes qualitatively depending on the spin parameter, a fact previously unknown. The number of observable critical points of the curvature invariants’ gradient fields along the axis of rotation changes at several transitional values of the spin parameter. These transitional values are a fundamental property of the Kerr metric. They are physically important since in general relativity these curvature invariants represent the cumulative tidal and frame-dragging effects of rotating black holes in an observer-independent way.

We carry out a comprehensive analysis of the possible constraints on cosmological and astrophysical parameters achievable with measurements of the thermal Sunyaev-Zel’dovich (tSZ) power spectrum from upcoming full-sky cosmic microwave background observations, with a particular focus on one-parameter extensions to the $\Lambda \mathrm{CDM}$ standard model involving local primordial non-Gaussianity (described by $f_{\mathrm{NL}}$) and massive neutrinos (described by $M_{\nu }$). We include all of the relevant physical effects due to these additional parameters, including the change to the halo mass function and the scale-dependent halo bias induced by local primordial non-Gaussianity. We use the halo model to compute the tSZ power spectrum and provide a pedagogical derivation of the one- and two-halo terms in an Appendix. We model the pressure profile of the intracluster medium (ICM) using a parametrized fit that agrees well with existing observations, and include uncertainty in the ICM modeling by including the overall normalization and outer logarithmic slope of the profile as free parameters. We compute forecasts for Planck, Primordial Inflation Explorer (PIXIE), and a cosmic variance (CV)-limited experiment, using multifrequency subtraction to remove foregrounds and implementing two masking criteria based on the ROSAT and eROSITA cluster catalogs to reduce the significant CV errors at low multipoles. We find that Planck can detect the tSZ power spectrum with $>30\sigma$ significance, regardless of the masking scenario. However, neither Planck or PIXIE is likely to provide competitive constraints on $f_{\mathrm{NL}}$ from the tSZ power spectrum due to CV noise at low $\ell$ overwhelming the unique signature of the scale-dependent bias. A future CV-limited experiment could provide a $3\sigma$ detection of $f_{\mathrm{NL}}\simeq 37$, which is the WMAP9 maximum-likelihood result. The outlook for neutrino masses is more optimistic: Planck can reach levels comparable to the current upper bounds $\lesssim 0.3\mathrm{eV}$ with conservative assumptions about the ICM; stronger ICM priors could allow Planck to provide $1\sigma –2\sigma$ evidence for massive neutrinos from the tSZ power spectrum, depending on the true value of the sum of the neutrino masses. We also forecast a $<10\%$ constraint on the outer slope of the ICM pressure profile using the unmasked Planck tSZ power spectrum.

The recent uncovering of the Fermi bubbles/haze in the Fermi $\gamma$-ray data has generated theoretical work to explain such a signal of hard $\gamma$ rays in combination with the WMAP haze signal. Many of these theoretical models can have distinctively different implications with regards to the production of high-energy neutrinos. We discuss the neutrino signals from different models proposed for the explanation of the Fermi bubbles/haze, more explicitly, from dark matter annihilation in the galactic halo with conditions of preferential cosmic ray diffusion, from recent active galactic nucleus jet activity, from periodic diffusive shock acceleration, from stochastic second order Fermi acceleration and from long time-scale star formation in the galactic center in combination with strong galactic winds. We find that some of these models will be probed by the IceCube DeepCore detector. Moreover, with a ${\mathrm{km}}^3$ telescope located in the Northern Hemisphere, we will be able to discriminate between the hadronic, leptonic and the dark matter models. Additionally using the reconstructed neutrino spectra we will probe annihilation of TeV scale dark matter towards the galactic center.

Detecting a stochastic gravitational wave background, particularly radiation from individually unresolvable supermassive black hole binary systems, is one of the primary targets for pulsar timing arrays. Increasingly more stringent upper limits are being set on these signals under the assumption that the background radiation is isotropic. However, some level of anisotropy may be present and the characterization of the gravitational wave energy density at different angular scales carries important information. We show that the standard analysis for isotropic backgrounds can be generalized in a conceptually straightforward way to the case of generic anisotropic background radiation by decomposing the angular distribution of the gravitational wave energy density on the sky into multipole moments. We introduce the concept of generalized overlap reduction functions which characterize the effect of the anisotropy multipoles on the correlation of the timing residuals from the pulsars timed by a pulsar timing array. In a search for a signal characterized by a generic anisotropy, the generalized overlap reduction functions play the role of the so-called Hellings and Downs curve used for isotropic radiation. We compute the generalized overlap reduction functions for a generic level of anisotropy and pulsar timing array configuration. We also provide an order of magnitude estimate of the level of anisotropy that can be expected in the background generated by supermassive black hole binary systems.

A folded resonant Fabry-Perot cavity has the potential to significantly reduce the impact of coating thermal noise on the performance of kilometer scale gravitational wave detectors. When constructed using only spherical mirror surfaces it is possible to utilize the extremely robust ${\mathrm{TEM}}_{00}$ mode optical mode. In this paper we investigate the potential thermal noise improvements that can be achieved for third generation gravitational wave detectors using realistic constraints. Comparing the previously proposed beam configurations such as e.g. higher order Laguerre-Gauss modes, we find that similar or better thermal noise improvement factors can be achieved, while avoiding degeneracy issues associated with those beams.

The sensitivity of searches for astrophysical transients in data from the Laser Interferometer Gravitational-wave Observatory (LIGO) is generally limited by the presence of transient, non-Gaussian noise artifacts, which occur at a high enough rate such that accidental coincidence across multiple detectors is non-negligible. These “glitches” can easily be mistaken for transient gravitational-wave signals, and their robust identification and removal will help any search for astrophysical gravitational waves. We apply machine-learning algorithms (MLAs) to the problem, using data from auxiliary channels within the LIGO detectors that monitor degrees of freedom unaffected by astrophysical signals. Noise sources may produce artifacts in these auxiliary channels as well as the gravitational-wave channel. The number of auxiliary-channel parameters describing these disturbances may also be extremely large; high dimensionality is an area where MLAs are particularly well suited. We demonstrate the feasibility and applicability of three different MLAs: artificial neural networks, support vector machines, and random forests. These classifiers identify and remove a substantial fraction of the glitches present in two different data sets: four weeks of LIGO’s fourth science run and one week of LIGO’s sixth science run. We observe that all three algorithms agree on which events are glitches to within 10% for the sixth-science-run data, and support this by showing that the different optimization criteria used by each classifier generate the same decision surface, based on a likelihood-ratio statistic. Furthermore, we find that all classifiers obtain similar performance to the benchmark algorithm, the ordered veto list, which is optimized to detect pairwise correlations between transients in LIGO auxiliary channels and glitches in the gravitational-wave data. This suggests that most of the useful information currently extracted from the auxiliary channels is already described by this model. Future performance gains are thus likely to involve additional sources of information, rather than improvements in the classification algorithms themselves. We discuss several plausible sources of such new information as well as the ways of propagating it through the classifiers into gravitational-wave searches.

The classical energy conditions are known to not be fundamental physics—they are typically violated by semiclassical quantum effects. Consequently, some effort has gone into finding possible semiclassical replacements for the classical energy conditions—the most well developed being the nonlocal time-integrated Ford-Roman quantum inequalities. In the current article we shall instead develop classical and quantum versions of a local “flux energy condition” (FEC and QFEC) based on the notion of constraining the possible fluxes measured by timelike observers. The naive classical FEC will be seen to be satisfied in some situations, and even for some quantum vacuum states, while its quantum analogue (the QFEC) is satisfied (for naturally defined quantum vacuum states) under a rather wide range of conditions. The situation for completely general (nonvacuum) quantum states is less clear.

The large forward-backward asymmetry of top quark pair production measured by hadron colliders sheds light on new physics signals beyond the Standard Model. In the warped extra dimension model with an additional $SU(3)$ group in the strong sector, we compare the cross section and forward-backward asymmetry of top quark pair production with recent data obtained by CDF and D0. Our numerical analysis shows that the parameter $c_q\ge 0.5$, $c_t\sim -0.6$, $\tan \varphi \ge 20$, and the first excitation of an axial gluon with a mass of about 5–6 TeV can accommodate this large anomaly without violating other experimental constraints. We show that a large ratio of strong couplings $g^D/g^S$ sets a strong limit on the parameter space of this model.

We explore the connection between pair production of dark matter particles at collider experiments and annihilation of dark matter in the early and late universe, with a focus on the correlation between the two time-reversed processes. We consider both a model-independent effective theory framework, where the initial and final states are assumed to not change under time reversal and concrete UV-complete models within the framework of supersymmetric extensions to the Standard Model. Even within the effective theory framework (where crossing symmetry is in some sense assumed), we find that the predictions of that symmetry can vary by orders of magnitude depending on the details of the selected effective interaction. Within the supersymmetric models we consider, we find that there is an even wilder variation in the expectations one can derive for collider observables based on cross-symmetric processes such as having a thermal relic or given indirect dark matter detection rates. We also explore additional “pitfalls” where naïve crossing symmetry badly fails, including models with very light mediators leading to Sommerfeld enhancements and/or dark matter bound states.

We consider a classically scale-invariant extension of the standard model in which a dark, non-Abelian gauge symmetry is spontaneously broken via the Coleman-Weinberg mechanism. Higgs portal couplings between the dark and standard model sectors provide an origin for the Higgs mass squared parameter and, hence, the electroweak scale. We find that choices for model parameters exist in which the dark gauge multiplet is viable as dark matter.

We investigate the effects of electroweak bremsstrahlung on binolike neutralino dark matter pair annihilations in the minimal supersymmetric standard model. We calculate the nonrelativistic pair annihilation cross sections via $W$-strahlung from leptonic final states, $\chi \chi \to W\ell \overline{\nu }$, and compare them with the contributions of the relevant two-body final states. We explore the case that sleptons lie below the TeV scale, while squarks are extremely heavy. It is found that the electroweak bremsstrahlung can give a dominant contribution to the cross section for some parameter regions which include slepton coannihilation regions with the observed relic abundance. We also evaluate the neutrino spectra at injection in the Sun. It is shown that energetic neutrinos via weak bremsstrahlung processes can be dominant over contributions of the two-body final states.

We study the production of the lightest neutralinos in the process $e^{+}{e}^{-}\to {\chi }_1^0{\chi }_1^0\gamma$ in supersymmetric grand unified models for the International Linear Collider energies with longitudinally polarized beams. We consider cases where the standard model gauge group is unified into the grand unified gauge groups $SU(5)$, or $SO(10)$. We have carried out a comprehensive study of this process in the $SU(5)$ and $SO(10)$ grand unified theories which includes the QED radiative corrections. We compare and contrast the dependence of the signal cross section on the grand unified gauge group, and on the different representations of the grand unified gauge group, when the electron and positron beams are longitudinally polarized. To assess the feasibility of experimentally observing the radiative production process, we have also considered in detail the background to this process coming from the radiative neutrino production process $e^{+}{e}^{-}\to \nu \overline{\nu }\gamma$ with longitudinally polarized electron and positron beams. In addition we have also considered the supersymmetric background coming from the radiative production of scalar neutrinos in the process $e^{+}{e}^{-}\to \tilde{\nu }{\tilde{\nu }}^{*}\gamma$ with longitudinally polarized beams. The process can be a major background to the radiative production of neutralinos when the scalar neutrinos decay invisibly.

We propose an experimental test of a scenario in the next-to-minimal supersymmetric standard model in which both the lightest scalar and the lightest pseudoscalar Higgs bosons have masses around 125 GeV. The pseudoscalar can contribute significantly to the $\gamma \gamma$ rate at the LHC due to light Higgsino-like charginos in its effective one-loop coupling to two photons. Such charginos are obtained for small values of the ${\mu }_{\mathrm{eff}}$ parameter, which also results in enhanced $b\overline{b}$ and ${\tau }^{+}{\tau }^{-}$ rates compared to those expected for a standard model (SM) Higgs boson. This scenario should result in a clear discrepancy between the observed rates in these three decay channels and those in the $WW$ and $ZZ$ channels, since the pseudoscalar does not couple to the $W$ and $Z$ bosons. However, in the dominant gluon fusion production mode, the pseudoscalar will stay hidden behind the SM-like scalar Higgs boson, and in order for it to be observable, the associated $b\overline{b}h$ production mode has to be considered, the cross section for which is tiny in the SM but $\tan \beta$-enhanced in supersymmetry. We analyze the constrained next-to-minimal supersymmetric standard model with nonuniversal Higgs sector parameters and identify regions of its parameter space where the lightest pseudoscalar with mass around 125 GeV and strongly enhanced $\gamma \gamma$ (up to 60%), $b\overline{b}$ and ${\tau }^{+}{\tau }^{-}$ rates in the $b\overline{b}h$ mode can be obtained.

The single spin asymmetry $A_N$, for large $P_T$ single inclusive particle production in $p^{\uparrow }p$ collisions, is considered within a generalized parton model and a transverse momentum dependent factorization scheme. The focus is on the Sivers effect and the study of its potential contribution to $A_N$, based on a careful analysis of the Sivers functions extracted from azimuthal asymmetries in semi-inclusive deep inelastic scattering processes. It is found that such Sivers functions could explain most features of the $A_N$ data, including some recent STAR results which show the persistence of a nonzero $A_N$ up to surprisingly large $P_T$ values.

We have studied the properties of quarkonium states in the presence of momentum anisotropy by correcting the full Cornell potential through the hard-loop resumed gluon propagator. The in-medium modification to the potential causes less screening, so quarkonium states become more tightly bound than in isotropic medium. In addition, the anisotropy in the momentum space introduces a characteristic angular dependence in the potential and as a result the quark pairs aligned in the direction of anisotropy are bound stronger than those of perpendicular alignment. Since the weak anisotropy represents a perturbation to the (isotropic) spherical potential, we use the quantum mechanical perturbation theory to obtain the first-order correction due to the small anisotropic contribution to the energy eigenvalues of spherically symmetric potential.

Higgs production in association with three jets via gluon fusion is an important channel for the measurement of the $\mathcal{C}\mathcal{P}$ properties of the Higgs particle at the LHC. In this paper, we go beyond the heavy top effective theory approximation and include at LO the full mass dependence of the top- and bottom-quark contributions. We consider the dominant subchannel $gg\to Hggg$ which involves the manipulation of massive rank-5 hexagon integrals. Furthermore, we present results for several differential distributions and show deviations from the effective theory as large as 100% at high $p_T$ for light Higgs masses.

We summarize and combine direct measurements of the mass of the $W$ boson in $\sqrt{s}=1.96\mathrm{TeV}$ proton-antiproton collision data collected by CDF and D0 experiments at the Fermilab Tevatron Collider. Earlier measurements from CDF and D0 are combined with the two latest, more precise measurements: a CDF measurement in the electron and muon channels using data corresponding to $2.2{\mathrm{fb}}^{-1}$ of integrated luminosity, and a D0 measurement in the electron channel using data corresponding to $4.3{\mathrm{fb}}^{-1}$ of integrated luminosity. The resulting Tevatron average for the mass of the $W$ boson is $M_W=80387\pm 16\mathrm{MeV}$. Including measurements obtained in electron-positron collisions at LEP yields the most precise value of $M_W=80385\pm 15\mathrm{MeV}$.

The results of searches for supersymmetry by the CMS experiment are interpreted in the framework of simplified models. The results are based on data corresponding to an integrated luminosity of 4.73 to $4.98{\mathrm{fb}}^{-1}$. The data were collected at the LHC in proton–proton collisions at a center-of-mass energy of 7 TeV. This paper describes the method of interpretation and provides upper limits on the product of the production cross section and branching fraction as a function of new particle masses for a number of simplified models. These limits and the corresponding experimental acceptance calculations can be used to constrain other theoretical models and to compare different supersymmetry-inspired analyses.

Gravitational waves with parallel rays are known to have remarkable properties: their orbit space of null rays possesses the structure of a nonrelativistic spacetime of codimension-1. Their geodesics are in one-to-one correspondence with dynamical trajectories of a nonrelativistic system. Similarly, the null dimensional reduction of Klein-Gordon’s equation on this class of gravitational waves leads to a Schrödinger equation on curved space. These properties are generalized to the class of gravitational waves with a null Killing vector field, of which we propose a new geometric definition, as conformally equivalent to the previous class and such that the Killing vector field is preserved. This definition is instrumental for performing this generalization, as well as various applications. In particular, results on geodesic completeness are extended in a similar way. Moreover, the classification of the subclass with constant scalar invariants is investigated.