We present the results of a study of Higgs triplet boson production arising in the littlest Higgs, left-right symmetric, and Georgi-Machacek models in the $W^{\pm }{W}^{\pm }$, $W^{\pm }Z$, $W^{+}{W}^{-}$, and $ZZ$ channels at the LHC. We focus on the “gold-plated” purely leptonic decay modes and consider the irreducible electroweak, QCD, and $t$-quark backgrounds, applying a combination of forward-jet tagging, central-jet vetoing, and stringent leptonic cuts to suppress the backgrounds. We find that, given the constraints on the triplet vacuum expectation value (vev), considerable luminosity is required to observe Higgs triplet bosons in vector boson scattering. Observing a Higgs triplet at the LHC is most promising in the Georgi-Machacek model due to a weaker constraint on the triplet vev. In this model, we find that a Higgs triplet boson with a mass of 1.0(1.5) TeV can be observed at the LHC with an integrated luminosity as low as $41(119){\mathrm{fb}}^{-1}$ in the $W^{\pm }{W}^{\pm }$ channel and as low as $171(474){\mathrm{fb}}^{-1}$ in the $W^{\pm }Z$ channel. Observation of Higgs triplet bosons in these channels would help identify the underlying theory.

We study the evolution of the plasma instabilities induced by two jets of particles propagating in opposite directions and crossing a thermally equilibrated non-Abelian plasma. In order to simplify the analysis we assume that the two jets of partons can be described with uniform distribution functions in coordinate space and by Gaussian distribution functions in momentum space. We find that while crossing the quark-gluon plasma, the jets of particles excite unstable chromomagnetic and chromoelectric modes. These fields interact with the particles (or hard modes) of the plasma inducing the production of currents; thus, the energy lost by the jets is absorbed by both the gauge fields and the hard modes of the plasma. We compare the outcome of the numerical simulations with the analytical calculation performed assuming that the jets of particles can be described by a tsunamilike distribution function. We find qualitative and semiquantitative agreement between the results obtained with the two methods.

The low energy neutrino factory has been proposed as a very sensitive setup for future searches for $CP$ violation and matter effects. Here we study how its performance is affected when the experimental specifications of the setup are varied. Most notably, we have considered the addition of the “platinum” ${\nu }_{\mu }\to {\nu }_e$ channel. We find that, while theoretically the extra channel provides very useful complementary information and helps to lift degeneracies, its practical usefulness is lost when considering realistic background levels. Conversely, an increase in statistics in the “golden” ${\nu }_e\to {\nu }_{\mu }$ channel and, to some extent, an improvement in the energy resolution, lead to an important increase in the performance of the facility, given the rich energy dependence of the “golden” channel at these energies. We show that a low energy neutrino factory with a baseline of 1300 km, muon energy of 4.5 GeV, and either a 20 kton totally active scintillating detector or 100 kton liquid argon detector, can have outstanding sensitivity to the neutrino oscillation parameters ${\theta }_{13}$, $\delta$, and the mass hierarchy. For our estimated exposure of $2.8\times {10}^{23}\mathrm{kton}\times \mathrm{\text{decays per muon polarity}}$, the low energy neutrino factory has sensitivity to ${\theta }_{13}$ and $\delta$ for ${sin}^2(2{\theta }_{13})>{10}^{-4}$ and to the mass hierarchy for ${sin}^2(2{\theta }_{13})>{10}^{-3}$.

Soft-wall models in AdS/QCD generally have dilaton and scalar fields that vary with the fifth-dimension coordinate. These fields can be parametrized to yield hadron mass spectra with linear radial trajectories and to incorporate spontaneous breaking of chiral symmetry. We show how to construct scalar potentials which lead to such solutions.

This paper explores the moduli-dependent coefficients of higher-derivative interactions that appear in the low-energy expansion of the four-supergraviton amplitude of maximally supersymmetric string theory compactified on a $d$ torus. These automorphic functions are determined for terms up to order ${\partial }^6{\mathcal{R}}^4$ and various values of $d$ by imposing a variety of consistency conditions. They satisfy Laplace eigenvalue equations with or without source terms, whose solutions are given in terms of Eisenstein series, or more general automorphic functions, for certain parabolic subgroups of the relevant $U$-duality groups. The ultraviolet divergences of the corresponding supergravity field theory limits are encoded in various logarithms, although the string theory expressions are finite. This analysis includes intriguing representations of $SL(d)$ and $SO(d,d)$ Eisenstein series in terms of toroidally compactified one and two-loop string and supergravity amplitudes.

Oscillons are extremely long lived, oscillatory, spatially localized field configurations that arise from generic initial conditions in a large number of nonlinear field theories. With an eye towards their cosmological implications, we investigate their properties in an expanding universe. We (1) provide an analytic solution for one-dimensional oscillons (for the models under consideration) and discuss their generalization to three dimensions, (2) discuss their stability against long wavelength perturbations, and (3) estimate the effects of expansion on their shapes and lifetimes. In particular, we discuss a new, extended class of oscillons with surprisingly flat tops. We show that these flat-topped oscillons are more robust against collapse instabilities in ($3+1$) dimensions than their usual counterparts. Unlike the solutions found in the small amplitude analysis, the width of these configurations is a nonmonotonic function of their amplitudes.

Building up on previous work, we present a new calculation of the gravitational wave emission generated during the transition from quasicircular inspiral to plunge, merger, and ringdown by a binary system of nonspinning black holes, of masses $m_1$ and $m_2$, in the extreme mass ratio limit, $m_1{m}_2\ll (m_1+m_2{)}^2$. The relative dynamics of the system is computed without making any adiabatic approximation by using an effective one body (EOB) description, namely, by representing the binary by an effective particle of mass $\mu =m_1{m}_2/(m_1+m_2)$ moving in a (quasi-)Schwarzschild background of mass $M=m_1+m_2$ and submitted to an $\mathcal{O}(\nu )$ 5PN-resummed analytical radiation reaction force, with $\nu =\mu /M$. The gravitational wave emission is calculated via a multipolar Regge-Wheeler-Zerilli-type perturbative approach (valid in the limit $\nu \ll 1$). We consider three mass ratios, $\nu =\{{10}^{-2},{10}^{-3},{10}^{-4}\}$, and we compute the multipolar waveform up to $\ell =8$. We estimate energy and angular momentum losses during the quasiuniversal and quasigeodesic part of the plunge phase and we analyze the structure of the ringdown. We calculate the gravitational recoil, or “kick,” imparted to the merger remnant by the gravitational wave emission and we emphasize the importance of higher multipoles to get a final value of the recoil $v/(c{\nu }^2)=0.0446$. We finally show that there is an excellent fractional agreement ($\sim {10}^{-3}$) (even during the plunge) between the 5PN EOB analytically resummed radiation reaction flux and the numerically computed gravitational wave angular momentum flux. This is a further confirmation of the aptitude of the EOB formalism to accurately model extreme-mass-ratio inspirals, as needed for the future space-based LISA gravitational wave detector.

Rapidly rotating neutron stars can be unstable to the gravitational-wave-driven Chandrasekhar-Friedman-Schutz (CFS) mechanism if they have a neutral point in the spectrum of nonaxisymmetric $f$-modes. We investigate the frequencies of these modes in two sequences of uniformly rotating polytropes using nonlinear simulations in full general relativity, determine the approximate locations of the neutral points, and derive limits on the observable frequency band available to the instability in these sequences. We find that general relativity enhances the detectability of a CFS-unstable neutron star substantially, both by widening the instability window and enlarging the band into the optimal range for interferometric detectors like LIGO, VIRGO, and GEO-600.

The inspiral of binary black holes is governed by gravitational radiation reaction at binary separations $r\lesssim 1000M$, yet it is too computationally expensive to begin numerical-relativity simulations with initial separations $r\gtrsim 10M$. Fortunately, binary evolution between these separations is well described by post-Newtonian equations of motion. We examine how this post-Newtonian evolution affects the distribution of spin orientations at separations $r\simeq 10M$ where numerical-relativity simulations typically begin. Although isotropic spin distributions at $r\simeq 1000M$ remain isotropic at $r\simeq 10M$, distributions that are initially partially aligned with the orbital angular momentum can be significantly distorted during the post-Newtonian inspiral. Spin precession tends to align (antialign) the binary black hole spins with each other if the spin of the more massive black hole is initially partially aligned (antialigned) with the orbital angular momentum, thus increasing (decreasing) the average final spin. Spin precession is stronger for comparable-mass binaries and could produce significant spin alignment before merger for both supermassive and stellar-mass black hole binaries. We also point out that precession induces an intrinsic accuracy limitation ($\lesssim 0.03$ in the dimensionless spin magnitude, $\lesssim 20°$ in the direction) in predicting the final spin resulting from the merger of widely separated binaries.

We investigate the linear cosmological perturbations in Hořava-Lifshitz gravity with a scalar field. Starting from the most general expressions of the metric perturbations as well as that of a canonical scalar field, we decompose the scalar, vector, and tensor parts of the perturbed action. By reducing the Hamiltonian, we find that there are two independent degrees of freedom for the tensor perturbations while none for the vector perturbations. For the scalar perturbations, the remaining number of degrees of freedom, which are all gauge invariant, depends on whether the projectable condition is applied or not: two when applied, with one of them being possibly a ghost, and one when not applied. For both cases, we lose the time reparametrization symmetry of any kind.

The numerical evolution of Einstein’s field equations in a generic background has the potential to answer a variety of important questions in physics: from applications to the gauge-gravity duality, to modeling black hole production in TeV gravity scenarios, to analysis of the stability of exact solutions, and to tests of cosmic censorship. In order to investigate these questions, we extend numerical relativity to more general space-times than those investigated hitherto, by developing a framework to study the numerical evolution of $D$ dimensional vacuum space-times with an $SO(D-2)$ isometry group for $D\ge 5$, or $SO(D-3)$ for $D\ge 6$. Performing a dimensional reduction on a ($D-4$) sphere, the $D$ dimensional vacuum Einstein equations are rewritten as a $3+1$ dimensional system with source terms, and presented in the Baumgarte, Shapiro, Shibata, and Nakamura formulation. This allows the use of existing $3+1$ dimensional numerical codes with small adaptations. Brill-Lindquist initial data are constructed in $D$ dimensions and a procedure to match them to our $3+1$ dimensional evolution equations is given. We have implemented our framework by adapting the Lean code and perform a variety of simulations of nonspinning black hole space-times. Specifically, we present a modified moving puncture gauge, which facilitates long-term stable simulations in $D=5$. We further demonstrate the internal consistency of the code by studying convergence and comparing numerical versus analytic results in the case of geodesic slicing for $D=5$, 6.

A possible process to destroy a black hole consists on throwing point particles with sufficiently large angular momentum into the black hole. In the case of Kerr black holes, it was shown by Wald that particles with dangerously large angular momentum are simply not captured by the hole, and thus the event horizon is not destroyed. Here, we reconsider this gedanken experiment for a variety of black hole geometries, from black holes in higher dimensions to black rings. We show that this particular way of destroying a black hole does not succeed and that cosmic censorship is preserved.

Inflation is studied in the context of asymptotically safe theories of gravitation. Conditions are explored under which it is possible to have a long period of nearly exponential expansion that eventually comes to an end.

We present constraints on the cosmic growth history with recent cosmological data, allowing for deviations from $\Lambda \mathrm{CDM}$ as might arise if cosmic acceleration is due to modifications to general relativity or inhomogeneous dark energy. We combine measures of the cosmic expansion history, from Type 1a supernovae, baryon acoustic oscillations, and the cosmic microwave background (CMB), with constraints on the growth of structure from recent galaxy, CMB, and weak lensing surveys along with integated Sachs Wolfe-galaxy cross correlations. Deviations from $\Lambda \mathrm{CDM}$ are parameterized by phenomenological modifications to the Poisson equation and the relationship between the two Newtonian potentials. We find modifications that are present at the time the CMB is formed are tightly constrained through their impact on the well-measured CMB acoustic peaks. By contrast, constraints on late-time modifications to the growth history, as might arise if modifications are related to the onset of cosmic acceleration, are far weaker, but remain consistent with $\Lambda \mathrm{CDM}$ at the 95% confidence level. For these late-time modifications we find that differences in the evolution on large and small scales could provide an interesting signature by which to search for modified growth histories with future wide angular coverage, large scale structure surveys.

It has been proposed that the gamma-ray burst–supernova connection may manifest itself in a significant fraction of core collapse supernovae possessing mildly relativistic jets with wide opening angles that do not break out of the stellar envelope. Neutrinos would provide proof of the existence of these jets. In the present paper we calculate the event rate of $\gtrsim 100\mathrm{GeV}$ neutrino-induced cascades in ${\mathrm{km}}^3$ detectors. We also calculate the event rate for $\gtrsim 10\mathrm{GeV}$ neutrinos of all flavors with the DeepCore low energy extension of IceCube. The added event rate significantly improves the ability of ${\mathrm{km}}^3$ detectors to search for these gamma-ray dark bursts. For a core collapse supernova at 10 Mpc we find $\sim 4$ events expected in DeepCore and $\sim 6$ neutrino-induced cascades in IceCube/KM3Net. Observations at $\gtrsim 10\mathrm{GeV}$ are mostly sensitive to the pion component of the neutrino production in the choked jet, while the $\gtrsim 100\mathrm{GeV}$ depends on the kaon component. Finally we discuss extensions of the ongoing optical follow-up programs by IceCube and Antares to include neutrinos of all flavors at $\gtrsim 10\mathrm{GeV}$ and neutrino-induced cascades at $\gtrsim 100\mathrm{GeV}$ energies.

As a test of the standard inflationary cosmology, which generically predicts a nearly scale-invariant spectrum of primordial curvature fluctuations, we perform a Markov-Chain Monte-Carlo analysis to search for possible modulations in the power spectrum and determine its shape together with the cosmological parameters using cosmic microwave background radiation data. By incorporating various three-parameter features on the simple power-law spectrum, we find an oscillatory modulation localized around the comoving wave number $k\simeq 0.009{\mathrm{Mpc}}^{-1}$ at 99.995% confidence level which improves the log-likelihood as much as $-\Delta 2\ln \mathcal{L}\equiv \Delta {\chi }_{\mathrm{eff}}^2=-22$. This feature can be detected even if we use only the cross correlation between the temperature and the E-mode polarization anisotropies.