Second-generation interferometric gravitational-wave detectors, such as Advanced LIGO and Advanced Virgo, are expected to begin operation by 2015. Such instruments plan to reach sensitivities that will offer the unique possibility to test general relativity in the dynamical, strong-field regime and investigate departures from its predictions, in particular, using the signal from coalescing binary systems. We introduce a statistical framework based on Bayesian model selection in which the Bayes factor between two competing hypotheses measures which theory is favored by the data. Probability density functions of the model parameters are then used to quantify the inference on individual parameters. We also develop a method to combine the information coming from multiple independent observations of gravitational waves, and show how much stronger inference could be. As an introduction and illustration of this framework—and a practical numerical implementation through the Monte Carlo integration technique of nested sampling—we apply it to gravitational waves from the inspiral phase of coalescing binary systems as predicted by general relativity and a very simple alternative theory in which the graviton has a nonzero mass. This method can (and should) be extended to more realistic and physically motivated theories.

We develop a numerical formulation to calculate the classical motion of charges in strong electromagnetic fields, such as those occurring in high-intensity laser beams. By reformulating the dynamics in terms of $SL(2,\mathbb{C})$ matrices representing the Lorentz group, our formulation maintains explicit covariance, in particular, the mass-shell condition. Considering an electromagnetic plane wave field where the analytic solution is known as a test case, we demonstrate the effectiveness of the method for solving both the Lorentz force and the Landau-Lifshitz equations. The latter, a second order reduction of the Lorentz-Abraham-Dirac equation, describes radiation reaction without the usual pathologies.

The quark-lepton complementarity (QLC) relations indicate a deep structure that interrelates quarks and leptons. We propose new scenarios, in a seesaw framework with discrete $A_4$ flavor symmetry, which can accommodate the QLC relations and the nonzero neutrino mixing angle ${\theta }_{13}$ together with all the available neutrino experimental data, in a consistent way to generate the Cabibbo-Kobayashi-Maskawa (CKM) matrix for the quark mixing. Certain effective dimension-5 operators are introduced, which induce a deviation of the lepton mixing matrix from the tribimaximal mixing pattern and lead the quark mixing matrix to the CKM one in form. We explicitly demonstrate three different possibilities of constructing the charged-lepton mixing matrix and point out that the phases of its elements play a crucial role to satisfy the QLC relations. We find that for the reactor mixing angle ${\theta }_{13}$ its possible values can vary around the center value $\sin {\theta }_{13}\simeq \lambda /\sqrt{2}$ ($\lambda \simeq 0.22$ being the Cabbibo angle) and have the lower bound ${\theta }_{13}\gtrsim 3.5°$. We also show that sizable leptonic $CP$ violation characterized by the Jarlskog invariant $|J_{CP}|\sim \mathcal{O}({10}^{-2})$ is allowed, which is expected to be tested in future experiments such as the upcoming long baseline neutrino oscillation ones.

The Lee-Wick (LW) standard model (SM) offers a new solution to the hierarchy problem. We discuss, using effective potential techniques, its peculiar UV behavior. We show how quadratic divergences in the Higgs mass $M_h$ cancel as a result of the unusual dependence of LW fields on the Higgs background (in a manner reminiscent of little Higgses). We then extract from the effective potential the renormalization group evolution of the Higgs quartic coupling $\lambda$ above the LW scale. After clarifying an apparent discrepancy with previous results for the LW Abelian Higgs model, we focus on the LWSM. In contrast with the SM case, for any $M_h$, $\lambda$ grows monotonically and hits a Landau pole at a fixed trans-Planckian scale (never turning negative in the UV). Then, the perturbativity and stability bounds on $M_h$ disappear. We identify a cutoff $\sim {10}^{16}\mathrm{GeV}$ for the LWSM due to the hypercharge gauge coupling hitting a Landau pole. Finally, we also discuss briefly the possible impact of the UV properties of the LW models on their behavior at finite temperature, in particular, regarding symmetry nonrestoration.

In general, charged Higgs bosons $H^{\pm }$ appear in nonminimal Higgs models. The $H^{\pm }{W}^{\mp }Z$ vertex is known to be related to the violation of the global symmetry (custodial symmetry) in the Higgs sector. Its magnitude strongly depends on the structure of the exotic Higgs models which contain higher isospin $SU(2{)}_L$ representations such as triplet Higgs bosons. We study the possibility of measuring the $H^{\pm }{W}^{\mp }Z$ vertex via single charged Higgs boson production associated with the $W^{\pm }$ boson at the International Linear Collider (ILC) by using the recoil method. The feasibility of the signal $e^{+}{e}^{-}\to H^{\pm }{W}^{\mp }\to \ell \nu jj$ is analyzed assuming the polarized electron and positron beams and the expected detector performance for the resolution of the two-jet system at the ILC. The background events can be reduced to a considerable extent by imposing the kinematic cuts even if we take into account the initial state radiation. For a relatively light charged Higgs boson whose mass $m_{H^{\pm }}$ is in the region of 120–130 GeV $<m_{H^{\pm }}<m_W+m_Z$, the $H^{\pm }{W}^{\mp }Z$ vertex would be precisely testable especially when the decay of $H^{\pm }$ is lepton specific. The exoticness of the extended Higgs sector can be explored by using combined information for this vertex and the rho parameter.

A method is proposed for distinguishing highly boosted hadronically-decaying $W$’s ($W$ jets) from QCD-jets using jet substructure. Previous methods, such as the filtering/mass-drop method, can give a factor of $\sim 2$ improvement in $S/\sqrt{B}$ for jet $p_T\gtrsim 200\mathrm{GeV}$. In contrast, a multivariate approach including new discriminants such as $R$ cores, which characterize the shape of the $W$ jet, subjet planar flow, and grooming-sensitivities is shown to provide a much larger factor of $\sim 5$ improvement in $S/\sqrt{B}$. For longitudinally polarized $W$’s, such as those coming from many new physics models, the discrimination is even better. Comparing different Monte Carlo simulations, we observe a sensitivity of some variables to the underlying event; however, even with a conservative estimates, the multivariate approach is very powerful. Applications to semileptonic $WW$ resonance searches and all-hadronic $W+\mathrm{\text{jet}}$ searches at the LHC are also discussed. Code implementing our $W$-jet tagging algorithm is publicly available at http://jets.physics.harvard.edu/wtag.

In the scenario with four quark generations, we perform a fit using flavor-physics data and determine the allowed values—preferred central values and errors—of all of the elements of the $4\times 4$ quark-mixing matrix. In addition to the direct measurements of some of the elements, we include in the fit the present measurements of several flavor-changing observables in the $K$ and $B$ systems that have small hadronic uncertainties, and also consider the constraints from the vertex corrections to $Z\to b\overline{b}$. The values taken for the masses of the fourth-generation quarks are consistent with the measurements of the oblique parameters and perturbativity of the Yukawa couplings. We find that $|{\tilde{V}}_{tb}|\ge 0.98$ at $3\sigma$, so that a fourth generation cannot account for any large deviation of $|V_{tb}|$ from unity. The fit also indicates that all the new-physics parameters are consistent with zero, and the mixing of the fourth generation with the other three is constrained to be small: we obtain $|{\tilde{V}}_{u{b}^{\prime }}|<0.06$, $|{\tilde{V}}_{c{b}^{\prime }}|<0.027$, and $|{\tilde{V}}_{t{b}^{\prime }}|<0.31$ at $3\sigma$. Still, this does allow for the possibility of new-physics signals in $B_d$, $B_s$ and rare $K$ decays.

We revisit the Higgs sector of the left-right supersymmetric model. We study the scalar potential in a version of the model in which the minimum is the charge-conserving vacuum state, without $R$-parity violation or additional nonrenormalizable terms in the Lagrangian. We analyze the dependence of the potential and of the Higgs mass spectrum on the various parameters of the model, pinpointing the most sensitive ones. We also show that the model can predict light neutral flavor-conserving Higgs bosons, while the flavor-violating ones are heavy and within the limits from $K^0-{\overline{K}}^0$, $D^0-{\overline{D}}^0$, and $B_{d,s}^0-{\overline{B}}_{d,s}^0$ mixings. We study variants of the model in which at least one doubly charged Higgs boson is light and show that the parameter space for such Higgs masses and mixings is very restrictive, thus making the model more predictive.

Recently, new reactor antineutrino spectra have been provided for ${}^{235}\mathrm{U}$, ${}^{239}\mathrm{Pu}$, ${}^{241}\mathrm{Pu}$, and ${}^{238}\mathrm{U}$, increasing the mean flux by about 3%. To a good approximation, this reevaluation applies to all reactor neutrino experiments. The synthesis of published experiments at reactor-detector distances $<100\mathrm{m}$ leads to a ratio of observed event rate to predicted rate of $0.976\pm 0.024$. With our new flux evaluation, this ratio shifts to $0.943\pm 0.023$, leading to a deviation from unity at 98.6% C.L. which we call the reactor antineutrino anomaly. The compatibility of our results with the existence of a fourth nonstandard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments, and MiniBooNE-$\nu$ data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that $|\Delta m_{\mathrm{new}}^2|>1.5{\mathrm{eV}}^2$ (95%) and ${sin}^2(2{\theta }_{\mathrm{new}})=0.14\pm 0.08$ (95%). Constraints on the ${\theta }_{13}$ neutrino mixing angle are revised.

We study Einstein gravity in dimensions $D\ge 4$ modified by curvature squared at critical point where the theory contains only massless gravitons. We show that at the critical point a new mode appears leading to a logarithmic gravity in the theory. The corresponding logarithmic solution may provide a gravity description of logarithmic conformal field theories (CFT) in higher dimensions. We note also that for special values of the parameters of the theory, the model admits solutions with nonrelativistic isometries.

The gravitational wave signal from an inspiralling binary neutron star system will contain detailed information about tidal coupling in the system, and thus, about the internal physics of the neutron stars. To extract this information will require highly accurate models for the gravitational waveform. We present here a calculation of the gravitational wave signal from a binary with quadrupolar tidal interactions which includes all post-1-Newtonian–order effects in both the conservative dynamics and wave generation. We consider stars with adiabatically induced quadrupoles moving in circular orbits, and work to linear order in the stars’ quadrupole moments. We find that post-1-Newtonian corrections increase the tidal signal by approximately 20% at gravitational wave frequencies of 400 Hz.

We apply a hybrid approach which combines loop and Fock quantizations to fully quantize the linearly polarized Gowdy $T^3$ model in the presence of a massless scalar field with the same symmetries as the metric. Like in the absence of matter content, the application of loop techniques leads to a quantum resolution of the classical cosmological singularity. Most importantly, thanks to the inclusion of matter, the homogeneous sector of the model contains flat Friedmann-Robertson-Walker solutions, which are not allowed in vacuo. Therefore, this model provides a simple setting to study at the quantum level interesting physical phenomena such as the effect of the anisotropies and inhomogeneities on flat Friedmann-Robertson-Walker cosmologies.

We use dimensional regularization to evaluate the one loop contribution to the graviton self-energy from a massless, minimally coupled scalar on a locally de Sitter background. For noncoincident points our result agrees with the stress tensor correlators obtained recently by Perez-Nadal, Roura, and Verdaguer. We absorb the ultraviolet divergences using the $R^2$ and $C^2$ counterterms first derived by ’t Hooft and Veltman, and we take the $D=4$ limit of the finite remainder. The renormalized result is expressed as the sum of two transverse, fourth order differential operators acting on nonlocal, de Sitter invariant structure functions. In this form it can be used to quantum correct the linearized Einstein equations so that one can study how the inflationary production of infrared scalars affects the propagation of dynamical gravitons and the force of gravity.

We study Drell-Yan production at the LHC in low-scale quantum gravity models with extra dimensions. Asymptotic safety implies that the ultraviolet behavior of gravity is dictated by a fixed point. We show how the energy dependence of Newton’s coupling regularizes the gravitational amplitude using a renormalization group improvement. We study LHC predictions and find that Kaluza-Klein graviton signals are well above standard model backgrounds. This leaves a significant sensitivity to the energy scale ${\Lambda }_T$ where the gravitational couplings crossover from classical to fixed point scaling.

The Standard Model (SM) plus a real gauge-singlet scalar field dubbed darkon ($\mathrm{SM}+D$) is the simplest model possessing a weakly interacting massive particle (WIMP) dark matter candidate. In this model, the parameters are constrained from dark matter relic density and direct searches. The fact that interaction between darkon and SM particles is only mediated by a Higgs boson exchange may lead to significant modifications to the Higgs boson properties. If the dark matter mass is smaller than half of the Higgs boson mass, then a Higgs boson can decay into a pair of darkons resulting in a large invisible branching ratio. The Higgs boson will be searched for at the LHC and may well be discovered in the near future. If a Higgs boson with a small invisible decay width will be found, the $\mathrm{SM}+D$ model with small dark matter mass will be in trouble. We find that by extending the $\mathrm{SM}+D$ to a two Higgs doublet model plus a darkon ($\mathrm{THDM}+D$) it is possible to have a Higgs boson with a small invisible branching ratio and at the same time the dark matter can have a low mass. We also comment on other implications of this model.

Growing neutrino quintessence solves the coincidence problem for dark energy by a growing cosmological value of the neutrino mass which emerges from a cosmon-neutrino interaction stronger than gravity. The cosmon-mediated attraction between neutrinos induces the formation of large-scale neutrino lumps in a recent cosmological epoch. We argue that the nonlinearities in the cosmon field equations stop the further increase of the neutrino mass within sufficiently dense and large lumps. As a result, we find the neutrino-induced gravitational potential to be substantially reduced when compared to linear extrapolations. We furthermore demonstrate that inside a lump the possible time variation of fundamental constants is much smaller than their cosmological evolution. This feature may reconcile current geophysical bounds with claimed cosmological variations of the fine structure constant.

We present the results of the estimation of parameters with LISA for nearly monochromatic gravitational waves in the low and high frequency regimes for the time-delay interferometry response. Angular resolution of the detector and the estimation errors of the signal’s parameters in the high frequency regimes are calculated as functions of the position in the sky and as functions of the frequency. For the long-wavelength domain we give compact formulas for the estimation errors valid on a wide range of the parameter space.

We consider two classes of supersymmetric flipped SU(5) models with gravity mediated supersymmetry breaking such that the thermal neutralino relic abundance provides the observed dark matter density in the universe. We estimate the muon flux induced by neutrinos that arise from neutralino annihilations in the Sun and discuss prospects for detecting this flux in the IceCube/Deep Core experiment. We also provide comparisons with the corresponding fluxes in the constrained minimal supersymmetric and nonuniversal Higgs models. Regions in the parameter space that can be explored by the IceCube/DeepCore experiment are identified.

We analyze the advantages of a linear-collider program for testing a recent theoretical proposal where the Higgs boson Yukawa couplings are radiatively generated, keeping unchanged the standard-model mechanism for electroweak-gauge-symmetry breaking. Fermion masses arise at a large energy scale through an unknown mechanism, and the standard model at the electroweak scale is regarded as an effective field theory. In this scenario, Higgs boson decays into photons and electroweak gauge-boson pairs are considerably enhanced for a light Higgs boson, which makes a signal observation at the LHC straightforward. On the other hand, the clean environment of a linear collider is required to directly probe the radiative fermionic sector of the Higgs boson couplings. Also, we show that the flavor-changing Higgs boson decays are dramatically enhanced with respect to the standard model. In particular, we find a measurable branching ratio in the range $({10}^{-4}–{10}^{-3})$ for the decay $H\to bs$ for a Higgs boson lighter than 140 GeV, depending on the high-energy scale where Yukawa couplings vanish. We present a detailed analysis of the Higgs boson production cross sections at linear colliders for interesting decay signatures, as well as branching-ratio correlations for different flavor-conserving/nonconserving fermionic decays.