Using data corresponding to $6.0{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the CDF II detector, we present a cross section measurement of top-quark pair production with an additional radiated photon in the central region with 10 GeV or more of transverse energy $t\overline{t}\gamma$. The events are selected by looking for a lepton ($\ell$ or $\mu$), a photon ($\gamma$), significant transverse momentum imbalance (${\mathrm{E̸}}_T$), large total transverse energy, and three or more jets, with at least one identified as containing a $b$ quark ($b$). Using an event selection optimized for the $t\overline{t}\gamma$ candidate sample, we also measure the cross section of $t\overline{t}$ (${\sigma }_{t\overline{t}}$). We measure the $t\overline{t}\gamma$ cross section (${\sigma }_{t\overline{t}\gamma }$) to be $0.18\pm 0.08\mathrm{pb}$, and the ratio of ${\sigma }_{t\overline{t}\gamma }$ to ${\sigma }_{t\overline{t}}$ to be $0.024\pm 0.009$. We observe a probability of 0.0015 (3.0 standard deviations) of the background (non-$t\overline{t}\gamma$ events alone producing 30 events or more.

The four-dimensional helicity regularization scheme is often used in one-loop QCD computations. It was recently argued in by [W. B. Kilgore, Phys. Rev. D 83, 114005 (2011)] that this scheme is inconsistent beyond the one-loop order in perturbation theory. In this paper, we clarify the reason for this inconsistency by studying the perturbative expansion of the vector current correlator in one-flavor QED through three-loop order. We develop a simple, practical way to fix the four-dimensional helicity scheme using the idea of dimensional reconstruction and demonstrate its application in several illustrative examples.

We search for $CP$ violation in a sample of 20 000 Cabibbo-suppressed decays, $D^{+}\to K^{+}{K}_S^0{\pi }^{+}{\pi }^{-}$, and 30 000 Cabibbo-favored decays, $D_s^{+}\to K^{+}{K}_S^0{\pi }^{+}{\pi }^{-}$. We use $520{\mathrm{fb}}^{-1}$ of data recorded by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider operating at center of mass energies near 10.6 GeV. We search for $CP$ violation in the difference between the $T$-odd asymmetries obtained using triple product correlations of the $D^{+}$ ($D_s^{+}$) and $D^{-}$ ($D_s^{-}$) decays, respectively. The $T$ violation parameter values obtained are ${\mathcal{A}}_T(D^{+})=(-12.0\pm {10.0}_{\mathrm{stat}}\pm {4.6}_{\mathrm{syst}})\times {10}^{-3}$ and ${\mathcal{A}}_T(D_s^{+})=(-13.6\pm {7.7}_{\mathrm{stat}}\pm {3.4}_{\mathrm{syst}})\times {10}^{-3}$, which are consistent with the standard model expectations.

It is known that the Maxwell theory in $D$ dimensions can be written in a first-order form (in derivatives) by introducing a totally antisymmetric field which leads to a ($D-3$)-form dual theory. Remarkably, one can replace the antisymmetric field by a symmetric rank-two tensor ($W_{\mu \nu }=W_{\nu \mu }$). Such master action establishes the duality between the Maxwell theory and a fourth-order higher-rank model in a $D$-dimensional flat space-time. A naive generalization to the curved space shows a connection between the recently found $D=4$ critical gravity and the Maxwell-theory plus a coupling term to the Ricci tensor ($R_{\mu \nu }{A}^{\mu }{A}^{\nu }$). The mass of the spin-1 particle which appears in the $D=4$ critical gravity linearized around anti-de Sitter space is the same one obtained from the Ricci coupling term. We also work out, in flat space-time, the explicitly massive case (Maxwell-Proca) which is dual to a second-order theory for $W_{\mu \nu }$.

In this paper we investigate gauged Wess-Zumino-Witten models for space-time groups as gravitational theories, following the trend of recent work by Anabalon, Willison, and Zanelli. We discuss the field equations in any dimension and study in detail the simplest case of two space-time dimensions and gauge group SO(2,1). For this model we study black hole solutions and we calculate their mass and entropy which resulted in a null value for both.

We develop and calibrate a characteristic waveform extraction tool whose major improvements and corrections of prior versions allow satisfaction of the accuracy standards required for advanced LIGO data analysis. The extraction tool uses a characteristic evolution code to propagate numerical data on an inner worldtube supplied by a $3+1$ Cauchy evolution to obtain the gravitational waveform at null infinity. With the new extraction tool, high accuracy and convergence of the numerical error can be demonstrated for an inspiral and merger of mass $M$ binary black holes even for an extraction worldtube radius as small as $R=20M$. The tool provides a means for unambiguous comparison between waveforms generated by evolution codes based upon different formulations of the Einstein equations and based upon different numerical approximations.

We develop the suggestion that dark matter could be a Bose-Einstein condensate. We determine the mass-radius relation of a Newtonian self-gravitating Bose-Einstein condensate with short-range interactions described by the Gross-Pitaevskii-Poisson system. We numerically solve the equation of hydrostatic equilibrium describing the balance between the gravitational attraction and the pressure due to quantum effects (Heisenberg’s uncertainty principle) and short-range interactions (scattering). We connect the noninteracting limit to the Thomas-Fermi limit. We also consider the case of attractive self-interaction. We compare the exact mass-radius relation obtained numerically with the approximate analytical relation obtained with a Gaussian ansatz. An overall good agreement is found.

We provide an approximate analytical expression of the mass-radius relation of a Newtonian self-gravitating Bose-Einstein condensate (BEC) with short-range interactions described by the Gross-Pitaevskii-Poisson system. These equations model astrophysical objects such as boson stars and, presumably, dark matter galactic halos. Our study connects the noninteracting case studied by Ruffini and Bonazzola (1969) to the Thomas-Fermi limit studied by Böhmer and Harko (2007). For repulsive short-range interactions (positive scattering lengths), there exists configurations of arbitrary mass but their radius is always larger than a minimum value. For attractive short-range interactions (negative scattering lengths), equilibrium configurations only exist below a maximum mass. Above that mass, the system is expected to collapse and form a black hole. We also study the radius versus scattering length relation for a given mass. We find that equilibrium configurations only exist above a (negative) minimum scattering length. Our approximate analytical solution, based on a Gaussian ansatz, provides a very good agreement with the exact solution obtained by numerically solving a nonlinear differential equation representing hydrostatic equilibrium. Our analytical treatment is, however, easier to handle and permits one to study the stability problem, and derive an expression of the pulsation period, by developing an analogy with a simple mechanical problem.

Faraday rotation induced B modes can provide a distinctive signature of primordial magnetic fields because of their characteristic frequency dependence and because they are only weakly damped on small scales, allowing them to dominate B modes from other sources. By numerically solving the full cosmic microwave background radiative transport equations, we study the B-mode power spectrum induced by stochastic magnetic fields that have significant power on scales smaller than the thickness of the last scattering surface. Constraints on the magnetic field energy density and inertial scale are derived from WMAP 7-year data, and are stronger than the big bang nucleosynthesis bound for a range of parameters. Observations of the cosmic microwave background polarization at smaller angular scales are crucial to provide tighter constraints or a detection.

A nonperturbative construction of the 3-point fermion-boson vertex which obeys its Ward-Takahashi or Slavnov-Taylor identity, ensures the massless fermion and boson propagators transform according to their local gauge covariance relations, reproduces perturbation theory in the weak coupling regime and provides a gauge independent description for dynamical chiral symmetry breaking and confinement has been a long-standing goal in physically relevant gauge theories such as quantum electrodynamics (QED) and quantum chromodynamics. In this paper, we demonstrate that the same simple and practical form of the vertex can achieve these objectives not only in 4-dimensional quenched QED but also in its 3-dimensional counterpart. Employing this convenient form of the vertex ansatz into the Schwinger-Dyson equation for the fermion propagator, we observe that it renders the critical coupling in 4-dimensional quenched QED markedly gauge independent in contrast with the bare vertex and improves on the well-known Curtis-Pennington construction. Furthermore, our proposal yields gauge independent order parameters for confinement and dynamical chiral symmetry breaking in 3-dimensional quenched QED.

We study the distance between symmetry-violating quantum field theories and the surface of symmetric theories. We use this notion to quantify how precise Lorentz symmetry is today, according to experimental data. The metric in parameter space is defined à la Zamolodchikov, from the two-point function of the Lagrangian perturbation. The distance is obtained minimizing the length of paths connecting the Lorentz-violating theory to the Lorentz surface. This definition depends on the Lagrangian used to formulate the theory, including total derivatives and the choice of coordinate frame. We eliminate such dependencies minimizing with respect to them. We derive a number of general formulas and evaluate the distance in the $CPT$-invariant, QED subsectors of the standard model extension and the renormalizable high-energy-Lorentz-violating standard model. We study the properties of the distance and address a number of applications.

We explore a novel method of mass reconstruction in events with missing energy at hadron colliders. In events with sizeable boost factors in the final steps of dual multistage decay chains, the missing energy particles may each be approximately collinear with a visible standard model particle, spanning a narrow “MET-cone.” We exploit this collinear approximation, when applicable, to reconstruct the masses of exotica.

Associated production of a baryonic $Z^{\prime }$ boson with the $W$ boson can account for the excess in $Wjj$ production observed by the CDF Collaboration at the Tevatron. We analyze other possible channels of this $Z^{\prime }$ at the Tevatron and at the LHC, including $\gamma Z^{\prime }$ and $Z{Z}^{\prime }$ with $Z^{\prime }\to jj$. We show that the chances of confirming this baryonic $Z^{\prime }$ are better at the Tevatron than at the LHC because of the faster growing backgrounds at the LHC. Unfortunately the current systematic uncertainties of the order of 10% cannot yield any significant excess in both the $\gamma Z^{\prime }$ and $Z{Z}^{\prime }$ channels at the Tevatron and also at the LHC. Nevertheless, the search using the $b\overline{b}$ decay mode of $Z^{\prime }$ is much more feasible at the LHC, provided that the branching ratio $B(Z^{\prime }\to b\overline{b})>0.1$. In particular, the $W{Z}^{\prime }\to \ell \nu b\overline{b}$ mode has a signal-to-background ratio larger than 1. Even with $1{\mathrm{fb}}^{-1}$ luminosity at the LHC, it can lead to a high significance level. The $W{Z}^{\prime }\to \ell \nu b\overline{b}$ and $\gamma Z^{\prime }\to \gamma b\overline{b}$ are also highly observable at the Tevatron.

The heavy quark spin symmetry implies that in addition to the recently observed $Z(10610)$ and $Z(10650)$ molecular resonances with $I^G=1^{+}$, there should exist two or four molecular bottomonium-like states with $I^G=1^{-}$. Properties of these $G$-odd states are considered, including their production in the radiative transitions from ${\rm Y}(5S)$, by applying the same symmetry to the ${\rm Y}(5S)$ resonance and the transition amplitudes. The considered radiative processes can provide a realistic option for observing the yet hypothetical states.

We propose, in a heuristic way, a relativistic modified gravity model as an alternative to particle dark matter at galactic scales. The model is based on a postulated preferred time foliation described by a dynamical scalar field called the Khronon. In coordinates adapted to the foliation, it appears as a modification of general relativity violating local Lorentz invariance in a regime of weak gravitational fields. The model is a particular case of noncanonical Einstein-æther theory, but in which the æther vector field is hypersurface-orthogonal. We show that this model recovers the phenomenology of the modified Newtonian dynamics (MOND) in the nonrelativistic limit, and predicts the same gravitational lensing as general relativity but with a modified Poisson-type potential.

We define the asymptotic flatness and discuss asymptotic symmetry at null infinity in arbitrary dimensions using the Bondi coordinates. To define the asymptotic flatness, we solve the Einstein equations and look at the asymptotic behavior of gravitational fields. Then we show the asymptotic symmetry and the Bondi mass loss law with the well-defined definition.

This paper presents results of an ongoing survey on the association between muon excesses at ground level, registered by the Tupi telescopes, and transient solar events, whose gamma-ray and x-ray emissions were reported by the Fermi Gamma Burst Monitor and the Geostationary Operational Environmental Satellite 14, respectively. We show that solar flares of small scale, those with prompt x-ray emission classified by the Geostationary Operational Environmental Satellite as C-Class with power ${10}^{-6}$ to ${10}^{-5}\mathrm{Watts}{\mathrm{m}}^{-2}$ at 1 AU, may give rise to muon excess probably associated with solar protons and ions emitted by the flare and arriving at the Earth as a coherent particle pulse. The Tupi telescopes are within the central region of the South Atlantic Anomaly, where the geomagnetic field intensity is the lowest on the Earth. Here we argue for the possibility of a “scale-free” power-law energy spectrum of particles accelerated by solar flares. For energies around and exceeding the pion production, large and small scale flares have the same power-law energy spectrum. The difference is only in the intensity. The Tupi events give support to this conjecture.

In this article we investigate the consequences of radiative flavor violation (RFV) in the minimal supersymmetric standard model. In this framework the small off-diagonal elements of the Cabibbo-Kobayashi-Maskawa (CKM) matrix and the small quark masses of the first two generations are generated from the trilinear supersymmetry-breaking terms. The impact of RFV on flavor-physics observables is studied in detail. We focus on the limiting cases in which the CKM matrix is either generated in the down sector, i.e. by the soft supersymmetry-breaking mass insertions ${\delta }_{i3}^{dLR}$ ($i=1$, 2), or in the up-quark sector, i.e. by the mass insertions ${\delta }_{i3}^{uLR}$. In the first case we find an enhancement of $b\to s\gamma$, which constrains the allowed range of sparticle masses (Fig. 3). In addition, neutral Higgs penguins significantly contribute to $B_{s,d}\to {\mu }^{+}{\mu }^{-}$ and, if also ${\delta }_{32}^{dLR}$ is different from zero, these Higgs effects are capable of explaining the observed $CP$ phase in the $B_s$ system. If, on the other hand, the CKM generation takes place in the up sector, $|{ϵ}_K|$ receives additional positive contributions enforcing large squark and gluino masses (see Fig. 8). In this case also the rare decay $K\to \pi \nu \overline{\nu }$ receives sizable contributions. In conclusion we find that for supersymmetry masses around 1 TeV RFV is an interesting alternative to minimal flavor violation.