We report the first complete calculation of QCD corrections to the production of a massive color-octet vector boson. Our next-to-leading-order (NLO) calculation includes both virtual corrections as well as corrections arising from the emission of gluons and light quarks, and we demonstrate the reduction in factorization-scale dependence relative to the leading-order approximation used in previous hadron collider studies. We show that the QCD NLO corrections to coloron production are as large as 30%, and that the residual factorization scale-dependence is reduced to of order 2%. We also calculate the $K$-factor and the $p_T$ spectrum for coloron production, since these are valuable for comparison with experiment. Our results apply directly to the production of the massive color-octet vector bosons in axigluon, topcolor, and coloron models, and approximately to the production of KK gluons in extra-dimensional models or color-octet technivector mesons in technicolor models.

We propose two 3-3-1 models (with either neutral fermions or right-handed neutrinos) based on $S_3$ flavor symmetry responsible for fermion masses and mixings. The models can be distinguished upon the new charge embedding ($\mathcal{L}$) relevant to lepton number. The neutrino small masses can be given via a cooperation of type I and type II seesaw mechanisms. The latest data on neutrino oscillation can be fitted provided that the flavor symmetry is broken via two different directions $S_3\to Z_2$ and $S_3\to Z_3$ (or equivalently in the sequel $S_3\to Z_2\to \{\mathrm{\text{Identity}}\}$), in which the second direction is due to a scalar triplet and another antisextet as small perturbation. In addition, breaking of either lepton parity in the model with neutral fermions or lepton number in the model with right-handed neutrinos must be happened due to the $\mathcal{L}$-violating scalar potential. The TeV seesaw scale can be naturally recognized in the former model. The degenerate masses of fermion pairs $(\mu ,\tau )$, $(c,t)$ and $(s,b)$ are, respectively, separated due to the $S_3\to Z_3$ breaking.

We present a search for the standard model Higgs boson production in association with a $W$ boson in proton-antiproton collisions ($p\overline{p}\to W^{\pm }H\to \ell \nu b\overline{b}$) at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately $2.7{\mathrm{fb}}^{-1}$. We recorded this data with two kinds of triggers. The first kind required high-${\mathrm{p}}_T$ charged leptons and the second required both missing transverse energy and jets. The search selects events consistent with a signature of a single lepton ($e^{\pm }/{\mu }^{\pm }$), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a jet probability tagging method. Kinematic information is fed in an artificial neural network to improve discrimination between signal and background. The search finds that both the observed number of events and the neural network output distributions are consistent with the standard model background expectations, and sets 95% confidence level upper limits on the production cross section times branching ratio. The limits are expressed as a ratio to the standard model production rate. The limits range from 3.6 (4.3 expected) to 61.1 (43.2 expected) for Higgs masses from 100 to $150\mathrm{GeV}/c^2$, respectively.

Galileon models arise in certain braneworld scenarios as modifications to general relativity, and are also interesting as field theories in their own right. We show how the Galileon model can be naturally generalized to include local gauge symmetries, by allowing for couplings to Yang-Mills fields. The resulting theories have at most second order spacetime derivatives in any representation of the gauge group, thereby avoiding Ostrogradski ghosts. We also extend the models to include curved space and show how, in that case we, need to include nonminimal couplings between the Galileons and the curvature tensors for the theory to retain its second order nature.

We attempt a critical reconsideration of “detailed balance” as a principle that can be used to restrict the proliferation of couplings in Hořava-Lifshitz gravity. We reexamine the shortcomings that have been usually associated with it in the literature and we argue that easy remedies can be found for all of them within the framework of detailed balance, and that the most persistent of them are actually related to projectability. We show that, once projectability is abandoned, detailed balance reduces the number of independent couplings by roughly an order of magnitude and imposes only one restriction that constitutes a phenomenological concern: the size of the (bare) cosmological constant is unacceptably large. Remarkably, this restriction (which is present in the projectable version as well) has been so far underappreciated in the literature. Optimists might prefer to interpret it as a potential blessing in disguise, as it allows one to entertain the idea of a miraculous cancellation between the bare cosmological constant and the (still poorly understood) vacuum energy contribution.

We study the symplectic reduction of the phase space of two twistors to the cotangent bundle of the Lorentz group. We provide expressions for the Lorentz generators and group elements in terms of the spinors defining the twistors. We use this to define twistor networks as a graph carrying the phase space of two twistors on each edge. We also introduce simple twistor networks, which provide a classical version of the simple projected spin networks living on the boundary Hilbert space of Engle, Pereira, Rovelli, Livine and Freidel, Krasnov spin foam models. Finally, we give an expression for the Haar measure in terms of spinors.

The eta-photon transition form factor is evaluated in a formalism based on a phenomenological description at low values of the photon virtuality, and a QCD-based description at high photon virtualities, matching at a scale $Q_0^2$. The high photon virtuality description makes use of a distribution amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars regularization at the matching scale $Q_0^2$, and QCD evolution from $Q_0^2$ to higher values of $Q^2$. A good description of the available data is obtained. The analysis indicates that the recent data from the BABAR collaboration on pion and eta transition form factor can be well reproduced, if a small contribution of higher twist is added to the dominant twist-two contribution at the matching scale $Q_0^2$.

In the era of the next generation of gravitational wave experiments a stochastic background from cusps of cosmic (super)strings is expected to be probed and, if not detected, to be significantly constrained. A popcornlike background can be, for part of the parameter space, as pronounced as the (Gaussian) continuous contribution from unresolved sources that overlap in frequency and time. We study both contributions from unresolved cosmic string cusps over a range of frequencies relevant to ground based interferometers, such as the LIGO/Virgo second generation and Einstein Telescope third generation detectors, the space antenna LISA, and pulsar timing arrays. We compute the sensitivity (at the $2\sigma$ level) in the parameter space for the LIGO/Virgo second generation detector, the Einstein Telescope detector, LISA, and pulsar timing arrays. We conclude that the popcorn regime is complementary to the continuous background. Its detection could therefore enhance confidence in a stochastic background detection and possibly help determine fundamental string parameters such as the string tension and the reconnection probability.

We discover the origin of the pathologies of the disorder parameter used in previous papers to detect dual superconductivity of QCD vacuum, and we remove them by defining an improved disorder parameter. A check of the approach is made by numerical simulations of $SU(2)$ gauge theory, which demonstrate that the approach is consistent and, with it, that deconfinement is a transition from dual superconductor to normal.

The $k=0$ Friedmann-Lemaitre-Robertson-Walker model with a positive cosmological constant and a massless scalar field is analyzed in detail. If one uses the scalar field as relational time, new features arise already in the Hamiltonian framework of classical general relativity: In a finite interval of relational time, the universe expands out to infinite proper time and zero matter density. In the deparametrized quantum theory, the true Hamiltonian now fails to be essentially self-adjoint both in the Wheeler-DeWitt approach and in loop quantum cosmology. Irrespective of the choice of the self-adjoint extension, the big-bang singularity persists in the Wheeler-DeWitt theory while it is resolved and replaced by a big bounce in loop quantum cosmology. Furthermore, the quantum evolution is surprisingly insensitive to the choice of the self-adjoint extension. This may be a special case of a yet-to-be discovered general property of a certain class of symmetric operators that fail to be essentially self-adjoint.

We have recently proposed a Lorentz-violating energy-momentum relation entailing an exact momentum cutoff and studied various physical applications of that dispersion law. By a simple phenomenological approach we study Lorentz violation effects on early Universe and pre-Planckian cosmological radiation. In particular, we predict an effective infinite speed of light soon after the big bang, leading to a possible solution of the horizon and flatness problems without recourse to inflation, cosmological scalar fields, or other ad hoc energy sources.

Close to a spacelike singularity, pure gravity and supergravity in 4 to 11 spacetime dimensions admit a cosmological billiard description based on hyperbolic Kac-Moody groups. We investigate the quantum cosmological billiards of relativistic wavepackets towards the singularity, employing flat and hyperbolic space descriptions for the quantum billiards. We find that the strongly chaotic classical billiard motion of four-dimensional pure gravity corresponds to a spreading wavepacket subject to successive redshifts and tending to zero as the singularity is approached. We discuss the possible implications of these results in the context of singularity resolution and compare them with those of known semiclassical approaches. As an aside, we obtain exact solutions for the one-dimensional relativistic quantum billiards with moving walls.

We present a model with dark matter in an anomaly-mediated supersymmetry breaking hidden sector with a $\mathrm{U}(1)\times \mathrm{U}(1)$ gauge symmetry. The symmetries of the model stabilize the dark matter and forbid the introduction of new mass parameters. As a result, the thermal relic density is completely determined by the gravitino mass and dimensionless couplings. Assuming nonhierarchical couplings, the thermal relic density is ${\Omega }_X\sim 0.1$, independent of the dark matter’s mass and interaction strength, realizing the WIMPless miracle. The model has several striking features. For particle physics, stability of the dark matter is completely consistent with $R$-parity violation in the visible sector, with implications for superpartner collider signatures; also the thermal relic’s mass may be $\sim 10\mathrm{GeV}$ or lighter, which is of interest given recent direct detection results. Interesting astrophysical signatures are dark matter self-interactions through a long-range force, and massless hidden photons and fermions that contribute to the number of relativistic degrees of freedom at big bang nucleosynthesis and cosmic microwave background. The latter are particularly interesting, given current indications for extra degrees of freedom and near future results from the Planck observatory.

We study a Dirac neutrino mass model of Davidson and Logan. In the model, the smallness of the neutrino mass is originated from the small vacuum expectation value of the second Higgs of two Higgs doublets. We study the one-loop effective potential of the Higgs sector and examine how the small vacuum expectation is stable under the radiative correction. By deriving formulas of the radiative correction, we numerically study how large the one-loop correction is and show how it depends on the quadratic mass terms and quartic couplings of the Higgs potential. The correction changes depending on the various scenarios for extra Higgs mass spectrum.

The standard model Higgs searches using the first $1–2{\mathrm{fb}}^{-1}$ of LHC data can be used to put interesting constraints on new scalar particles other than the Higgs particle. We investigate one such scenario in which electroweak symmetry is broken via strongly coupled conformal dynamics. This scenario contains a neutral scalar dilaton—the Goldstone boson associated with spontaneously broken scale invariance—with a mass below the conformal symmetry breaking scale and couplings to standard model particles similar (but not identical) to those of the standard model Higgs boson. We translate the LEP and LHC Higgs limits to constrain the dilaton mass and conformal breaking scale. The conformal breaking scale $f$ is constrained to be above 1 TeV for dilaton masses between 145 and 600 GeV, though it can be as low as 400 GeV for dilaton masses below 110 GeV. We also show that (i) a dilaton $\chi$ with mass below 110 GeV and consistent with the LEP constraints can appear in $gg\to \chi \to \gamma \gamma$ with a rate up to $\sim 10$ times the corresponding standard model Higgs rate, and (ii) a dilaton with mass of several hundred GeV is much narrower than the corresponding standard model Higgs bosons, leading to improved search sensitivity in $\chi \to ZZ\to 4\ell$.

We determine the strangeness and light quark fractions of the nucleon mass by computing the quark line connected and disconnected contributions to the matrix elements $m_q⟨N|\overline{q}q|N⟩$ in lattice QCD, using the nonperturbatively improved Sheikholeslami-Wohlert Wilson fermionic action. We simulate $n_{\mathrm{F}}=2$ mass degenerate sea quarks with a pion mass of about 285 MeV and a lattice spacing $a\approx 0.073\mathrm{fm}$. The renormalization of the matrix elements involves mixing between contributions from different quark flavors. The pion-nucleon $\sigma$ term is extrapolated to physical quark masses exploiting the sea quark mass dependence of the nucleon mass. We obtain the renormalized values ${\sigma }_{\pi N}=(38\pm 12)\mathrm{MeV}$ at the physical point and $f_{T_s}={\sigma }_s/m_N=0.012(14{)}_{-3}^{+10}$ for the strangeness contribution at our larger than physical sea quark mass.

The thick center vortex model, with the idea of using domain structures, is used to calculate the potentials between two G(2) heavy sources in the fundamental, the adjoint, and the 27-dimensional representations. The potentials are screened at large distances. This behavior is expected from the thick center vortex model since G(2) has only a trivial center element which makes no contribution to the average Wilson loop at the large distance regime. A linear potential is obtained at intermediate distances for all representations. This behavior can be explained by the thickness of the vortices (domains) and by defining a flux for the trivial center element of G(2). The role of the SU(3) subgroup of G(2) in the linear regime is also discussed. The string tensions are in rough agreement with the Casimir operators of the corresponding representations.

We study heavy baryons with exotic flavor quantum numbers formed by a heavy meson and a nucleon ($\overline{D}N$ and $BN$) with positive parity. One-pion-exchange interaction, providing a tensor force, dominates as a long-range force to bind the $\overline{D}N$ and $BN$ systems. In the heavy-quark mass limit, pseudoscalar meson and vector meson are degenerate and the binding mechanism by the tensor force analogous to that in the nuclear systems becomes important. As a result, we obtain the $\overline{D}N$ and $BN$ resonant states in the $J^P=1/2^{+}$, $3/2^{+}$, and $5/2^{+}$ channels with $I=0$.

We consider top quark pair production in association with a hard jet through next-to-leading order in perturbative QCD. Top quark decays are treated in the narrow width approximation and spin correlations are retained throughout the computation. We include hard jet radiation by top quark decay products and explore their importance for basic kinematic distributions at the Tevatron and the LHC. Our results suggest that QCD corrections and jet radiation in decays can lead to significant changes in shapes of basic distributions and, therefore, need to be included for the description of $t\overline{t}j$ production.

We examine loop-mediated effects of new heavy quarks $Q=(t^{\prime },b^{\prime })$ on $t\overline{t}$ production at hadron colliders, using a phenomenological model with flavor off-diagonal couplings of charged and neutral scalars $\varphi =({\varphi }^{\pm },{\varphi }^0)$ to $Q$. We show that an invariant-mass-dependent asymmetry, in the $t\overline{t}$ center of mass, consistent with those recently reported by the CDF collaboration, can be obtained for quark masses around 350–500 GeV, scalar masses of order 100–200 GeV, and modest-to-strong Yukawa couplings. The requisite strong interactions suggest a nonperturbative electroweak-symmetry-breaking mechanism and composite states at the weak scale. A typical prediction of this framework is that the new heavy quarks decay dominantly into $t\varphi$ final states.