Current searches for gravitational waves from compact-object binaries with the LIGO and Virgo observatories employ waveform models with spins aligned (or antialigned) with the orbital angular momentum. Here, we derive a new statistic to search for compact objects carrying generic (precessing) spins. Applying this statistic, we construct banks of both aligned- and generic-spin templates for binary black holes and neutron star–black hole binaries, and compare the effectualness of these banks towards simulated populations of generic-spin systems. We then use these banks in a pipeline analysis of Gaussian noise to measure the increase in background incurred by using generic- instead of aligned-spin banks. Although the generic-spin banks have roughly a factor of ten more templates than the aligned-spin banks, we find an overall improvement in signal recovery at a fixed false-alarm rate for systems with high-mass ratio and highly precessing spins. This gain in sensitivity comes at a small loss of sensitivity ($\lesssim 4\%$) for systems that are already well covered by aligned-spin templates. Since the observation of even a single binary merger with misaligned spins could provide unique astrophysical insights into the formation of these sources, we recommend that the method described here be developed further to mount a viable search for generic-spin binary mergers in LIGO/Virgo data.

We obtain a large class of Lorentzian wormhole spacetimes in scalar-tensor gravity, for which the matter stress energy does satisfy the weak energy condition. Our constructions have zero Ricci scalar and an everywhere finite, nonzero scalar field profile. Interpreting the scalar-tensor gravity as an effective on-brane theory resulting from a two-brane Randall-Sundrum model of warped extra dimensions, it is possible to link wormhole existence with that of extra dimensions. We study the geometry, matter content, gravitational redshift and circular orbits in such wormholes and argue that our examples are perhaps among those which may have some observational relevance in astrophysics in the future. We also study traversability and find that our wormholes are indeed traversable for values of the metric parameters satisfying the weak energy condition.

We study the evolution of the rotation rate of a proto-neutron star, born in a core-collapse supernova, in the first seconds of its life. During this phase, the star evolution can be described as a sequence of stationary configurations, which we determine by solving the neutrino transport and the stellar structure equations in general relativity. We include in our model the angular momentum loss due to neutrino emission. We find that the requirement of a rotation rate not exceeding the mass-shedding limit at the beginning of the evolution implies a strict bound on the rotation rate at later times. Moreover, assuming that the proto-neutron star is born with a finite ellipticity, we determine the emitted gravitational wave signal and estimate its detectability by present and future ground-based interferometric detectors.

A central feature of the most elementary rotating black hole (BH) solution in general relativity is the Kerr bound which, for vacuum Kerr BHs, can be expressed either in terms of the Arnowitt-Deser-Misner (ADM) or horizon “charges.” However, this bound is not a fundamental property of general relativity and stationary, asymptotically flat, and regular (on and outside an event horizon) BHs are known to violate the Kerr bound, in terms of both their ADM and horizon quantities. Examples include the recently discovered Kerr BHs with scalar [C. A. R. Herdeiro and E. Radu, Phys. Rev. Lett. 112, 221101 (2014)] or Proca hair [C. Herdeiro, E. Radu, and H. Runarsson, arXiv:1603.02687]. Here, we point out the fact that the Kerr bound in terms of horizon quantities is also violated by well-known rotating and charged solutions which are known in closed form, such as the Kerr-Newman and Kerr-Sen BHs. Moreover, for the former we observe that the Reissner-Nordström (RN) bound is also violated in terms of horizon quantities, even in the static (i.e., RN) limit. By contrast, for the latter the existence of charged matter outside the horizon allows for a curious invariance of the charge-to-mass ratio between the ADM and horizon quantities. Regardless of the Kerr bound violation, we show that in all cases the event horizon linear velocity [C. A. R. Herdeiro and E. Radu, Int. J. Mod. Phys. D 24, 1544022 (2015)] never exceeds the speed of light. Finally, we suggest a new type of informative parametrization for BH spacetimes where part of the asymptotic charge is supported outside the horizon.

We use a description based on differential forms to systematically explore the space of scalar-tensor theories of gravity. Within this formalism, we propose a basis for the scalar sector at the lowest order in derivatives of the field and in any number of dimensions. This minimal basis is used to construct a finite and closed set of Lagrangians describing general scalar-tensor theories invariant under local Lorentz transformations in a pseudo-Riemannian manifold, which contains ten physically distinct elements in four spacetime dimensions. Subsequently, we compute their corresponding equations of motion and find which combinations are at most second order in derivatives in four as well as an arbitrary number of dimensions. By studying the possible exact forms (total derivatives) and algebraic relations between the basis components, we discover that there are only four Lagrangian combinations producing second-order equations, which can be associated with Horndeski’s theory. In this process, we identify a new second-order Lagrangian, named kinetic Gauss-Bonnet, that was not previously considered in the literature. However, we show that its dynamics is already contained in Horndeski’s theory. Finally, we provide a full classification of the relations between different second-order theories. This allows us to clarify, for instance, the connection between different covariantizations of Galileons theory. In conclusion, our formulation affords great computational simplicity with a systematic structure. As a first step, we focus on theories with second-order equations of motion. However, this new formalism aims to facilitate advances towards unveiling the most general scalar-tensor theories.

In this work, we investigate localized and extended objects for gravitating, self-interacting phantom fields. The phantom fields come from two scalar fields with a “wrong-sign” (negative) kinetic energy term in the Lagrangian. This study covers several solutions supported by these phantom fields: phantom balls, traversable wormholes, phantom cosmic strings, and “phantom” domain walls. These four systems are solved numerically, and we try to draw out general, interesting features in each case.

We study the simplest two-body problem in asymptotically anti-de Sitter spacetime: two, infinitely thin, concentric spherical shells of matter. We include only gravitational interaction between the two shells, but we show that the dynamics of this system is highly nontrivial. We observe prompt collapse to a black hole, delayed collapse and even perpetual oscillatory motion, depending on the initial location of the shells (or their energy content). The system exhibits critical behavior, and we show strong hints that it is also chaotic.

In the context of ($2+1$)–dimensional $SL(N,\mathbb{R})\times SL(N,\mathbb{R})$ Chern-Simons theory we explore issues related to regularity and asymptotics on the solid torus, for stationary and circularly symmetric solutions. We display and solve all necessary conditions to ensure a regular metric and metriclike higher spin fields. We prove that holonomy conditions are necessary but not sufficient conditions to ensure regularity, and that Hawking conditions do not necessarily follow from them. Finally we give a general proof that once the chemical potentials are turned on—as demanded by regularity—the asymptotics cannot be that of Brown-Henneaux.

Current constraints on spatial curvature show that it is dynamically negligible: $|{\mathrm{\Omega }}_{\mathrm{K}}|\lesssim 5\times {10}^{-3}$ (95% C.L.). Neglecting it as a cosmological parameter would be premature however, as more stringent constraints on ${\mathrm{\Omega }}_{\mathrm{K}}$ at around the ${10}^{-4}$ level would offer valuable tests of eternal inflation models and probe novel large-scale structure phenomena. This precision also represents the “curvature floor,” beyond which constraints cannot be meaningfully improved due to the cosmic variance of horizon-scale perturbations. In this paper, we discuss what future experiments will need to do in order to measure spatial curvature to this maximum accuracy. Our conservative forecasts show that the curvature floor is unreachable—by an order of magnitude—even with Stage IV experiments, unless strong assumptions are made about dark energy evolution and the $\mathrm{\Lambda }\mathrm{CDM}$ parameter values. We also discuss some of the novel problems that arise when attempting to constrain a global cosmological parameter like ${\mathrm{\Omega }}_{\mathrm{K}}$ with such high precision. Measuring curvature down to this level would be an important validation of systematics characterization in high-precision cosmological analyses.

The cosmic microwave background (CMB) is one of the finest probes of cosmology. Its all-sky temperature and linear polarization fluctuations have been measured precisely at a level of $\delta T/T_{\mathrm{CMB}}\sim {10}^{-6}$. In contrast, circular polarization ($CP$) of the CMB has not been precisely explored. The current upper limit on the $CP$ of the CMB is at a level of $\delta V/T_{\mathrm{CMB}}\sim {10}^{-4}$ and is limited on large scales. Some of the cosmologically important sources which can induce a $CP$ in the CMB include early Universe symmetry breaking, a primordial magnetic field, galaxy clusters, and Pop III stars (also known as the first stars). Among these sources, Pop III stars are expected to induce the strongest signal with levels strongly dependent on the frequency of observation and on the number, $N_p$, of the Pop III stars per halo. Optimistically, a $CP$ signal in the CMB resulting from the Pop III stars could be at a level of $\delta V/T_{\mathrm{CMB}}\sim 2\times {10}^{-7}$ in scales of 1° at 10 GHz, which is much smaller than the currently existing upper limits on the $CP$ measurements. Primary foregrounds in the cosmological $CP$ detection will come from the galactic synchrotron emission, which is naturally (intrinsically) circularly polarized. We use data-driven models of the galactic magnetic field, thermal electron density, and relativistic electron density to simulate all-sky maps of the galactic $CP$. This work also points out that the galactic $CP$ levels are important below 50 GHz and is an important factor for telescopes aiming to detect primordial B modes using $CP$ as a systematic rejection channel. In this paper, we focus on a SNR evaluation for the detectability of the Pop III induced $CP$ signal in the CMB. We find that a SNR higher than unity is achievable, for example, with a 10 m telescope and an observation time of 20 months at 10 GHz, if $N_p\ge 100$. We also find that, if frequency of observation and resolution of the beam is appropriately chosen, a SNR higher than unity is possible with $N_p\ge 10$ and resolution per pixel $\sim 1\mu \mathrm{K}$ at an observation time of 60 months.

The separate universe technique provides a means of establishing consistency relations between short-wavelength observables and the long-wavelength matter density fluctuations within which they evolve by absorbing the latter into the cosmological background. We extend it to cases where nongravitational forces introduce a Jeans scale in other species like dynamical dark energy or massive neutrinos. The technique matches the synchronous gauge matter density fluctuations to the local expansion using the acceleration equation and accounts for the temporal nonlocality and scale dependence of the long-wavelength response of small scale matter observables, e.g., the nonlinear power spectrum, halo abundance and the implied halo bias, and $N$-point correlation functions. Above the Jeans scale, the local Friedmann equation relates the expansion to real energy densities and a curvature that is constant in comoving coordinates. Below the Jeans scale, the curvature evolves and acts like a fake density component. In all cases, the matter evolution on small scales is correctly modeled as we illustrate using scalar field dark energy with adiabatic or isocurvature initial conditions across the Jeans scale set by its finite sound speed.

Direct detection of black hole-neutron star pairs is anticipated with the advent of aLIGO. Electromagnetic counterparts may be crucial for a confident gravitational-wave detection as well as for extraction of astronomical information. Yet black hole-neutron star pairs are notoriously dark and so inaccessible to telescopes. Contrary to this expectation, a bright electromagnetic transient can occur in the final moments before merger as long as the neutron star is highly magnetized. The orbital motion of the neutron star magnet creates a Faraday flux and corresponding power available for luminosity. A spectrum of curvature radiation ramps up until the rapid injection of energy ignites a fireball, which would appear as an energetic blackbody peaking in the x ray to $\gamma$ rays for neutron star field strengths ranging from ${10}^{12}$ to ${10}^{16}\mathrm{G}$ respectively and a $10M_{\odot }$ black hole. The fireball event may last from a few milliseconds to a few seconds depending on the neutron star magnetic-field strength, and may be observable with the Fermi Gamma-Ray Burst Monitor with a rate up to a few per year for neutron star field strengths $\gtrsim {10}^{14}\mathrm{G}$. We also discuss a possible decaying post-merger event which could accompany this signal. As an electromagnetic counterpart to these otherwise dark pairs, the black-hole battery should be of great value to the development of multi-messenger astronomy in the era of aLIGO.

We derive the gravitational waveform from the collapse of a rapidly rotating supermassive star (SMS) core leading directly to a seed of a supermassive black hole (SMBH) in axisymmetric numerical-relativity simulations. We find that the peak strain amplitude of gravitational waves emitted during the black hole formation is $\approx 5\times {10}^{-21}$ at the frequency $f\approx 5\mathrm{mHz}$ for an event at the cosmological redshift $z=3$, if the collapsing SMS core is in the hydrogen-burning phase. Such gravitational waves will be detectable by space laser interferometric detectors like eLISA with signal-to-noise ratio $\approx 10$, if the sensitivity is as high as LISA for $f=1–10\mathrm{mHz}$. The detection of the gravitational wave signal will provide a potential opportunity for testing the direct-collapse scenario for the formation of a seed of SMBHs.

Probing the Higgs potential and new physics behind the electroweak symmetry breaking is one of the most important issues of particle physics. In particular, the nature of the electroweak phase transition is essential for understanding the physics of the early Universe, such that the strongly first-order phase transition is required for a successful scenario of electroweak baryogenesis. The strongly first-order phase transition is expected to be tested by precisely measuring the triple Higgs boson coupling at future colliders like the International Linear Collider. It can also be explored via the spectrum of stochastic gravitational waves to be measured at future space-based interferometers such as eLISA and DECIGO. We discuss the complementarity of both the methods in testing the strongly first-order phase transition of the electroweak symmetry in models with additional isospin singlet scalar fields with and without classical scale invariance. We find that they are synergetic in identifying specific models of electroweak symmetry breaking in more detail.

Models of compositeness can successfully address the origin of the Higgs boson, as a pseudo-Nambu-Goldstone boson (pNGB) of a spontaneously broken global symmetry, and flavor physics via the partial compositeness mechanism. If the dynamics is generated by a confining gauge group with fermionic matter content, there exists only a finite set of models that have the correct properties to account for the Higgs and top partners at the same time. In this paper, we explore the theory space of this class of models; remarkably, all of them contain—beyond the pNGB Higgs—a pNGB singlet, $a$, which couples to Standard Model gauge bosons via Wess-Zumino-Witten interactions, thus providing naturally a resonance in the diboson at the LHC. With the assumption that the recently reported diphoton excess at 750 GeV at the LHC arises from the $a$ resonance, we propose a generic approach on how to delineate the best candidate for composite Higgs models with top partners. We find that constraints from other diboson searches severely reduce the theory space of the models under consideration. For the models which can explain the diphoton excess, we make precise and testable predictions for the width and other diboson resonance searches.

We investigate the phenomenology of a model based on the $SU(3{)}_c\times SU(3{)}_L\times U(1{)}_X$ gauge theory, the so-called 331 model. In particular, we focus on the Higgs sector of the model which is composed of three $SU(3{)}_L$ triplet Higgs fields and is the minimal form for realizing a phenomenologically acceptable scenario. After the spontaneous symmetry breaking $SU(3{)}_L\times U(1{)}_X\to SU(2{)}_L\times U(1{)}_Y$, our Higgs sector effectively becomes that with two $SU(2{)}_L$ doublet scalar fields, in which the first- and the second-generation quarks couple to a different Higgs doublet from that which couples to the third-generation quarks. This structure causes the flavor-changing neutral current mediated by Higgs bosons at the tree level. By taking an alignment limit of the mass matrix for the $CP$-even Higgs bosons, which is naturally realized in the case with the breaking scale of $SU(3{)}_L\times U(1{)}_X$ much larger than that of $SU(2{)}_L\times U(1{)}_Y$, we can avoid current constraints from flavor experiments such as the $B^0\text{−}{\overline{B}}^0$ mixing even for the Higgs bosons masses that are $\mathcal{O}(100)\mathrm{GeV}$. In this allowed parameter space, we clarify that a characteristic deviation in quark Yukawa couplings of the Standard Model–like Higgs boson is predicted, which has a different pattern from that seen in two Higgs doublet models with a softly broken $Z_2$ symmetry. We also find that the flavor-violating decay modes of the extra Higgs boson, e.g., $H/A\to tc$ and $H^{\pm }\to ts$, can be dominant, and they yield the important signature to distinguish our model from the two Higgs doublet models.

We follow up on a suggestion by Adams and construct explicit domain wall fermion operators with staggered kernels. We compare different domain wall formulations, namely the standard construction as well as Boriçi’s modified and Chiu’s optimal construction, utilizing both Wilson and staggered kernels. In the process, we generalize the staggered kernels to arbitrary even dimensions and introduce both truncated and optimal staggered domain wall fermions. Some numerical investigations are carried out in the ($1+1$)-dimensional setting of the Schwinger model, where we explore spectral properties of the bulk, effective and overlap Dirac operators in the free-field case, on quenched thermalized gauge configurations and on smooth topological configurations. We compare different formulations using the effective mass, deviations from normality and violations of the Ginsparg-Wilson relation as measures of chirality.

The strength of the amplitudes for the coupling between the bottomonium $\mathrm{\Upsilon }(nS)$ states, the bottomonium-like isovector resonances $Z_b$ and a pion, $\mathrm{\Upsilon }(nS)Z_b\pi$, is considered. These amplitudes describe the decays $Z_b\to \mathrm{\Upsilon }(nS)\pi$ for $n=1$, 2, 3, and the processes $\mathrm{\Upsilon }(nS)\to Z_b\pi$ for $n=5,6,\dots$ with either $Z_b(10610)$ or $Z_b(10650)$. It is pointed out that analyticity and unitarity impose a sum rule for these couplings to each of the $Z_b$ resonances. With the currently available data it appears to be difficult or impossible to simultaneously satisfy the sum rules for the $Z_b(10610)$ and $Z_b(10650)$ resonances. This difficulty can be resolved if there is a considerable dissimilarity in the yield of the states $Z_b(10610)\pi$ and $Z_b(10650)\pi$ in the $e^{+}{e}^{-}$ annihilation at energies above the $\mathrm{\Upsilon }(5S)$ resonance.