We present a study of the branching fraction of the decay $B^0\to {\rho }^0{\rho }^0$ and the fraction of longitudinally polarized ${\rho }^0$ mesons in this decay. The results are obtained from the final data sample containing $772\times 10^6$ $B\overline{B}$ pairs collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We find $166\pm 59$ $B^0\to {\rho }^0{\rho }^0$ events (including systematic uncertainties), corresponding to a branching fraction of $\mathcal{B}(B^0\to {\rho }^0{\rho }^0)=(1.02\pm 0.30(\text{stat})\pm 0.15(\text{syst}))\times 10^{-6}$ with a significance of 3.4 standard deviations and a longitudinal polarization fraction $f_L=0.21_{-0.22}^{+0.18}(\text{stat})\pm 0.15(\text{syst})$. We use the longitudinal polarization fraction to determine the Cabibbo-Kobayashi-Maskawa matrix angle ${\varphi }_2=(84.9\pm 13.5)°$ through an isospin analysis in the $B\to \rho \rho$ system. We furthermore find $125\pm 41$ $B^0\to f_0{\rho }^0$ events, corresponding to $\mathcal{B}(B^0\to f_0{\rho }^0)\times \mathcal{B}(f_0\to {\pi }^{+}{\pi }^{-})=(0.78\pm 0.22(\text{stat})\pm 0.11(\text{syst}))\times 10^{-6}$, with a significance of 3.1 standard deviations. We find no other significant contribution with the same final state, and set upper limits at 90% confidence level on the (product) branching fractions, $\mathcal{B}(B^0\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-})<11.2\times 10^{-6}$, $\mathcal{B}(B^0\to {\rho }^0{\pi }^{+}{\pi }^{-})<12.0\times 10^{-6}$, $\mathcal{B}(B^0\to f_0{\pi }^{+}{\pi }^{-})\times \mathcal{B}(f_0\to {\pi }^{+}{\pi }^{-})<3.0\times 10^{-6}$ and $\mathcal{B}(B^0\to f_0{f}_0)\times \mathcal{B}(f_0\to {\pi }^{+}{\pi }^{-}{)}^2<0.2\times 10^{-6}$.

The neutral current $e^{\pm }p$ cross section has been measured up to values of Bjorken $x\cong 1$ with the ZEUS detector at HERA using an integrated luminosity of $187{\mathrm{pb}}^{-1}$ of $e^{-}p$ and $142{\mathrm{pb}}^{-1}$ of $e^{+}p$ collisions at $\sqrt{s}=318\mathrm{GeV}$. Differential cross sections in $x$ and $Q^2$, the exchanged boson virtuality, are presented for $Q^2\ge 725{\mathrm{GeV}}^2$. An improved reconstruction method and greatly increased amount of data allows a finer binning in the high-$x$ region of the neutral current cross section and leads to a measurement with much improved precision compared to a similar earlier analysis. The measurements are compared to Standard Model expectations based on a variety of recent parton distribution functions.

We determine the fraction of events with double parton (DP) scattering in a single $p\overline{p}$ collision at $\sqrt{s}=1.96\mathrm{TeV}$ in samples of $\gamma +3$ jet and $\gamma +b/c\text{jet}+2$ jet events collected with the D0 detector and corresponding to an integrated luminosity of about $8.7{\mathrm{fb}}^{-1}$. The DP fractions and effective cross sections (${\sigma }_{\text{eff}}$) are measured for both event samples using the same kinematic selections. The measured DP fractions range from 0.21 to 0.17, with effective cross sections in the $\gamma +3$ jet and $\gamma +b/c\text{jet}+2$ jet samples of ${\sigma }_{\text{eff}}^{\text{incl}}=12.7\pm 0.2(\text{stat})\pm 1.3(\text{syst})\mathrm{mb}$ and ${\sigma }_{\text{eff}}^{\text{HF}}=14.6\pm 0.6(\text{stat})\pm 3.2(\text{syst})\mathrm{mb}$, respectively.

We investigate the collision of a point particle and an infinitely thin planar domain wall interacting gravitationally within linearized gravity in a Minkowski space-time of arbitrary dimension. In this setting we are able to describe analytically the perforation of the wall by an impinging particle, showing that it is accompanied by an excitation of the spherical branon shock wave propagating outwards with the speed of light. Formally, the shock wave is a free solution of the branon wave equation which has to be added to ensure the validity of the retarded solution at the perforation point. Physically, the domain wall gets excited due to the shake caused by an instantaneous change of sign of the repulsive gravitational force. This effect is shown to hold, in particular, in four space-time dimensions, which is applicable to the problem of cosmological domain walls.

The structure of singularities in perturbative massless gauge theories is investigated in coordinate space. The pinch singularities in coordinate-space integrals occur at configurations of vertices which have a direct interpretation in terms of the physical scattering of particles in real space-time in the same way as for the loop momenta in the case of momentum-space singularities. In the analysis of vertex functions in coordinate space, the well-known factorization into hard, soft, and jet functions is found. By power-counting arguments, it is found that coordinate-space integrals of vertex functions have logarithmic divergences at worst.

Using the renormalization group framework we classify different extensions of the standard model according to their degree of naturality. A new relevant class of perturbative models involving elementary scalars is the one in which the theory simultaneously satisfies the Veltman conditions and is conformal at the classical level. We term these extensions perturbative natural conformal (PNC) theories. We show that PNC models are very constrained and thus highly predictive. Among the several PNC examples that we exhibit, we discover a remarkably simple PNC extension of the standard model in which the Higgs is predicted to have the experimental value of the mass equal to 126 GeV. This model also predicts the existence of one more standard model singlet scalar boson with a mass of 541 GeV and the Higgs self-coupling to emerge radiatively. We study several other PNC examples that generally predict a somewhat smaller mass of the Higgs to the perturbative order we have investigated them. Our results can be a useful guide when building extensions of the standard model featuring fundamental scalars.

Photon quantization is implemented in the standard model extension (SME) using the Gupta-Bleuler method and Becchi-Rouet-Stora-Tyutin concepts. The quantization prescription applies to both the birefringent and nonbirefringent $CPT$-even couplings. A curious incompatibility is found between the presence of the Lorentz-violating terms and the existence of a nontrivial conjugate momentum ${\mathrm{\Pi }}^0$ yielding problems with covariant quantization procedure. An introduction of a mass regulator term can avoid the vanishing of ${\mathrm{\Pi }}^0$ and allows for the implementation of a covariant quantization procedure. Field-theoretic calculations involving the SME photons can then be performed using the mass regulator, similar to the conventional procedure used in electrodynamics for infrared-divergence regulation.

In the current paper the properties of a birefringent Lorentz-violating extension of quantum electrodynamics is considered. The theory results from coupling modified Maxwell theory, which is a $CPT$-even Lorentz-violating extension of the photon sector, to a Dirac theory of standard spin-$1/2$ particles. It is then restricted to a special birefringent case with one nonzero Lorentz-violating coefficient. The modified dispersion laws of electromagnetic waves are obtained plus their phase and group velocities are considered. After deriving the photon propagator and the polarization vectors for a special momentum configuration we prove both unitarity at tree level and microcausality for the quantum field theory based on this Lorentz-violating modification. These analytical proofs are done for a spatial momentum with two vanishing components and the proof of unitarity is supported by numerical investigations in case all components are nonvanishing. The upshot is that the theory is well behaved within the framework of our assumptions where there is a possible issue for negative Lorentz-violating coefficients. The paper shall provide a basis for the future analysis of alternative birefringent quantum field theories.

In gauge theories the presence of constraints can obstruct expressing the global Hilbert space as a tensor product of the Hilbert spaces corresponding to degrees of freedom localized in complementary regions. In algebraic terms, this is due to the presence of a center—a set of operators which commute with all others—in the gauge invariant operator algebra corresponding to a finite region. A unique entropy can be assigned to algebras with a center, giving a place to a local entropy in lattice gauge theories. However, ambiguities arise on the correspondence between algebras and regions. In particular, it is always possible to choose (in many different ways) local algebras with a trivial center, and hence a genuine entanglement entropy, for any region. These choices are in correspondence with maximal trees of links on the boundary, which can be interpreted as partial gauge fixings. This interpretation entails a gauge fixing dependence of the entanglement entropy. In the continuum limit, however, ambiguities in the entropy are given by terms local on the boundary of the region, in such a way relative entropy and mutual information are finite, universal, and gauge independent quantities.

Two-point correlators and self-correlators of primordial perturbations in quasi–de Sitter spacetime backgrounds are considered. For large separations two-point correlators exhibit nearly scale invariance, while for short distances self-correlators need standard renormalization. We study the deformation of two-point correlators to smoothly match the self-correlators at coincidence. The corresponding angular power spectrum is evaluated in the Sachs-Wolfe regime of low multipoles. Scale invariance is maintained, but the amplitude of $C_{\ell }$ could change in a nontrivial way.

Transient orbital resonances have recently been identified as potentially important to the inspiral of small bodies into large black holes. These resonances occur as the inspiral evolves through moments in which two fundamental orbital frequencies, ${\mathrm{\Omega }}_{\theta }$ and ${\mathrm{\Omega }}_r$, are in a small integer ratio to one another. Previous work has demonstrated that a binary’s parameters are “kicked” each time the inspiral passes through a resonance, changing the orbit’s characteristics relative to a model that neglects resonant effects. In this paper, we use exact Kerr geodesics coupled to an accurate but approximate model of inspiral to survey orbital parameter space and estimate how commonly one encounters long-lived orbital resonances. We find that the most important resonances last for a few hundred orbital cycles at mass ratio ${10}^{-6}$, and that resonances are almost certain to occur during the time that a large-mass-ratio binary would be a target of gravitational wave observations. Resonances appear to be ubiquitous in large-mass-ratio inspiral, and to last long enough that they are likely to affect binary evolution in observationally important ways.

Motivations for the existence of a fundamental preferred frame range from pure phenomenology to attempts to solve the nonrenormalizability of quantum gravity, the problem of time (and scale), and the cosmological constant problem(s). In many explicit constructions, such as Einstein-Aether or gravitational aether theories, $k$-essence, cuscuton theory, shape dynamics, or (nonprojectable) Hořava-Lifshitz gravity, the low-energy theory contains a fluid (which defines a preferred frame) with superluminal or incompressible excitations. We study here the formation of black holes in the presence of such a fluid. In particular, we focus on the incompressible limit of the fluid (or constant mean curvature foliation) in the spacetime of a spherically collapsing shell within an asymptotically cosmological spacetime. In this case, ignoring the fluid backreaction, we can analytically show that an observer inside $3/4$ of the Schwarzschild radius cannot send a signal outside, after a stage in collapse, even using signals that propagate infinitely fast in the preferred frame. This confirms the dynamical emergence of universal horizons that have been previously found in static solutions. We argue that this universal horizon should be considered as the future boundary of the classical spacetime.

The inspiral of a stellar mass ($1-100M_{\odot }$) compact body into a massive ($10^5-10^7{M}_{\odot }$) black hole has been a focus of much effort, both for the promise of such systems as astrophysical sources of gravitational waves, and because they are a clean limit of the general relativistic two-body problem. Our understanding of this problem has advanced significantly in recent years, with much progress in modeling the “self-force” arising from the small body’s interaction with its own spacetime deformation. Recent work has shown that this self-interaction is especially interesting when the frequencies associated with the orbit’s $\theta$ and $r$ motions are in an integer ratio: ${\mathrm{\Omega }}_{\theta }/{\mathrm{\Omega }}_r={\beta }_{\theta }/{\beta }_r$, with ${\beta }_{\theta }$ and ${\beta }_r$ both integers. In this paper, we show that key aspects of the self-interaction for such “resonant” orbits can be understood with a relatively simple Teukolsky-equation-based calculation of gravitational-wave fluxes. We show that fluxes from resonant orbits depend on the relative phase of radial and angular motions. The purpose of this paper is to illustrate in simple terms how this phase dependence arises using tools that are good for strong-field orbits, and to present a first study of how strongly the fluxes vary as a function of this phase and other orbital parameters. Future work will use the full dissipative self-force to examine resonant and near resonant strong-field effects in greater depth, which will be needed to characterize how a binary evolves through orbital resonances.

We present exact spherically symmetric null dust solutions in the third-order Lovelock gravity with a string cloud background in arbitrary $N$ dimensions. This represents radiating black holes and generalizes the well-known Vaidya solution to Lovelock gravity with a string cloud in the background. We also discuss the energy conditions and horizon structures and explicitly bring out the effect of the string clouds on the horizon structure of black hole solutions for the higher-dimensional general relativity and Einstein-Gauss-Bonnet theories. It turns out that the presence of the coupling constant of the Gauss-Bonnet terms and/or background string clouds completely changes the structure of the horizon and this may lead to a naked singularity. We recover known spherically symmetric radiating models as well as static black holes in the appropriate limits.

We discuss how dynamical dark energy universes with exotic singularities may be distinguished from the standard $\mathrm{\Lambda }\mathrm{CDM}$ model on the basis of their redshift drift signal, for which measurements both in the acceleration phase and in the deep matter era will be provided by forthcoming astrophysical facilities. Two specific classes of exotic singularity models are studied: sudden future singularity models and finite scale factor singularity models. In each class we identify the models which can mimic $\mathrm{\Lambda }\mathrm{CDM}$ and play the role of dark energy as well as models for which redshift drift signals are significantly different from $\mathrm{\Lambda }\mathrm{CDM}$ and the test can differentiate between them.

We discuss a number of experimental constraints on Weinberg’s Higgs portal model. In this framework, the standard model (SM) particle spectrum is extended to include one complex scalar field $S$ and one Dirac fermion $\psi$. These new fields are singlets under the SM gauge group and are charged under a global $U(1)$ symmetry. Breaking of this $U(1)$ symmetry results in a massless Goldstone boson $\alpha$ and a massive $CP$-even scalar $r$ and splits the Dirac fermion into two new mass-eigenstates ${\psi }_{\pm }$, corresponding to Majorana fermions. The interest on such a minimal SM extension is twofold. On the one hand, if the Goldstone bosons are in thermal equilibrium with SM particles until the era of muon annihilation, their contribution to the effective number of neutrino species can explain the hints from cosmological observations of extra relativistic degrees of freedom at the epoch of last scattering. On the other hand, the lightest Majorana fermion ${\psi }_{-}$ provides a plausible dark matter candidate. Mixing of $r$ with the Higgs doublet $\varphi$ is characterized by the mass of hidden scalar $m_h$ and the mixing angle $\theta$. We constrain this parameter space using a variety of experimental data, including heavy meson decays with missing energy, the invisible Higgs width, and direct dark matter searches. We show that different experimental results compress the allowed parameter space in complementary ways, covering a large range of ${\psi }_{-}$ masses ($5\lesssim m_{-}\lesssim 100\mathrm{GeV}$). Though current results narrow the parameter space significantly (for the mass range of interest, $\theta \lesssim {10}^{-3}$ to ${10}^{-4}$), there is still room for discovery ($\alpha$ decoupling at the muon annihilation era requires $\theta \gtrsim {10}^{-5}$ to ${10}^{-4}$). In the near future, measurements from ATLAS, CMS, LHCb, NA62, XENON1T, LUX, and CDMSlite will probe nearly the full parameter space.

The aim of this paper is to extend, clarify, and deepen the results of our previous work [D. M. Lucchesi and R. Peron, Phys. Rev. Lett. 105, 231103 (2010)], related to the precise measurement of LAGEOS (LAser GEOdynamics Satellite) II pericenter shift. A 13-year time span of LAGEOS satellites’ laser tracking data has been considered, obtaining a very precise orbit and correspondingly residuals time series from which to extract the relevant signals. A thorough description is provided of the data analysis strategy and the dynamical models employed, along with a detailed discussion of the known sources of error in the experiment, both statistical and systematic. From this analysis, a confirmation of the predictions of Einstein’s general relativity, as well as strong bounds on alternative theories of gravitation, clearly emerge. In particular, taking conservatively into account the stricter error bound due to systematic effects, general relativity has been confirmed in the Earth’s field at the 98% level (meaning the measurement of a suitable combination of $\beta$ and $\gamma$ PPN parameters in weak-field conditions). This bound has been used to constrain possible deviations from the inverse-square law parameterized by a Yukawa-like new long range interaction with strength $|\alpha |\lesssim 1\times {10}^{-10}$ at a characteristic range $\lambda \simeq 1$ Earth radius, a possible nonsymmetric gravitation theory with the interaction parameter ${\mathcal{C}}_{\oplus \text{LAGEOS II}}{\lesssim \text{(9 × 10}}^{-2}\mathrm{km}{)}^4$, and a possible spacetime torsion with a characteristic parameter combination $|2t_2+t_3|\lesssim 7\times 10^{-2}$. Conversely, if we consider the results obtained from our best fit of the LAGEOS II orbit, the constraints in fundamental physics improve by at least 2 orders of magnitude.

This paper presents new results on the combined sensitivity of the LHC and underground dark matter search experiments to the lightest neutralino as a weakly interacting massive particle candidate in the minimal supersymmetric extension of the standard model. We show that monojet searches significantly extend the sensitivity to the neutralino mass in scenarios where scalar quarks are nearly degenerate in mass with it. The inclusion of the latest bound by the LUX experiment on the neutralino-nucleon spin-independent scattering cross section expands this sensitivity further, highlighting the remarkable complementarity of $\text{jets}/\ell \mathrm{s}+$ missing transverse energy and monojets at the LHC, and dark matter searches in probing models of new physics with a dark matter candidate. The qualitative results of our study remain valid after accounting for theoretical uncertainties.

Although the Large Hadron Collider (LHC) has not observed supersymmetric (SUSY) partners of the Standard Model particles, their existence is not ruled out yet. One recently explored scenario in which there are light SUSY partners that have evaded current bounds from the LHC is that of a light long-lived stop quark. In this paper we consider light stop pair production at the LHC when the stop mass is between 200 and 400 GeV. If the stops are long-lived they can form a bound state, stoponium, which then undergoes two-body decays to Standard Model particles. By considering the near-threshold production of such a pair through the gluon-gluon fusion process and taking into account the strong Coulombic interactions responsible for the formation of this bound state, we obtain factorization theorems for the stop pair inclusive and differential production cross sections. We also perform a resummation of large threshold logarithms up to next-to-next-to-leading logarithmic accuracy using well-established renormalization group equations in an effective field theory methodology. These results are used to calculate the invariant mass distributions of two photons or two $Z$ bosons coming from the decay of the stoponium at the LHC. For our choices of SUSY model parameters, the stoponium is not detectable above Standard Model backgrounds in $\gamma \gamma$ or $ZZ$ at 8 TeV, but will be visible with $400{\mathrm{fb}}^{-1}$ of accumulated data if its mass is below 500 GeV when the LHC runs at 14 TeV.

The simplest extension of the two Higgs doublet model is the addition of a real scalar singlet, $S$. The effects of mixing between the singlet and the doublets can be manifested in two ways. It can modify the couplings of the 126 GeV Higgs boson, $h$, and it can lead to direct detection of the heavy Higgs at the LHC. In this paper, we show that in the type-I model, for heavy Higgs masses in the 200–600 GeV range, the latter effect will be detected earlier than the former for most of parameter space. Should no such Higgs be discovered in this mass range, then the upper limit on the mixing will be sufficiently strong such that there will be no significant effects on the couplings of the $h$ for most of parameter space. The reverse is true in the type-II model: the limits from measurements of the couplings of the $h$ will dominate over the limits from nonobservation of the heavy Higgs.