Motivated by the recent interest in cosmologies arising from energy density modifications to the Friedmann equation, we analyze the scaling behavior for a broad class of these cosmologies comprised of scalar fields and background barotropic fluid sources. In particular, we determine the corresponding scalar field potentials which lead to attractor scaling solutions in a wide class of braneworld and dark energy scenarios. We show how a number of recent proposals for modifying the Friedmann equation can be thought of as being dual to one another, and determine the conditions under which such dualities arise.

We study symmetry restoration at finite temperature in the theory of a charged scalar field interacting with a constant, external magnetic field. We compute the finite-temperature effective potential including the contribution from ring diagrams. We show that in the weak field case, the presence of the field produces a stronger first order phase transition and that the temperature for the onset of the transition is lower, as compared to the case without magnetic field.

In the scenario recently proposed by Arkani-Hamed and Dimopoulos, the supersymmetric scalar particles are all very heavy, at least of the order of ${10}^9\mathrm{G}\mathrm{e}\mathrm{V}$ but the gauginos, Higgsinos, and one of the neutral Higgs bosons remain under a TeV. The most distinct signature is the metastable gluino. However, the detection of metastable gluino depends crucially on the spectrum of hadrons that it fragments into. Instead, here we propose another unambiguous signature by forming the gluino-gluino bound state, gluinonium, which will then annihilate into $t\overline{t}$ and $b\overline{b}$ pairs. We study the sensitivity of such signatures at the LHC.

We investigate the impact parameter dependent parton distributions for a relativistic composite system in light-front framework. We take an effective two-body spin-$1/2$ state, namely, an electron dressed with a photon in QED. We express the impact parameter dependent parton distributions in terms of overlaps of light-cone wave functions. We obtain the scale dependence of both fermion and gauge boson distributions and show the distortion of the parton distributions in the transverse space for transverse polarization of the state at one loop level.

We report on a search for standard model $t$-channel and $s$-channel single-top quark production in $p\overline{p}$ collisions at a center of mass energy of 1.96 TeV. We use a data sample corresponding to $162\mathrm{p}{\mathrm{b}}^{-1}$ recorded by the upgraded collider detector at Fermilab. We find no significant evidence for electroweak top quark production and set upper limits at the 95% confidence level on the production cross section, consistent with the standard model: 10.1 pb for the $t$-channel, 13.6 pb for the $s$-channel and 17.8 pb for the combined cross section of $t$- and $s$-channel.

We generalize the flow equations approach to inflationary model building to the Randall–Sundrum Type II braneworld scenario. As the flow equations are quite insensitive to the expansion dynamics, we find results similar to, though not identical to, those found in the standard cosmology.

Real time excitations in the broken symmetry phase of the classical Abelian Higgs model are investigated numerically in the unitary gauge. Spectral equations of state of its constituent quasiparticles are extracted. Characteristic differences between the statistical correlations of the transverse and of the longitudinal vector modes with the Higgs field are exposed. A method is proposed for the reconstruction of the quasifree composite field coordinates.

We present a new three-dimensional fully general-relativistic hydrodynamics code using high-resolution shock-capturing techniques and a conformal traceless formulation of the Einstein equations. Besides presenting a thorough set of tests which the code passes with very high accuracy, we discuss its application to the study of the gravitational collapse of uniformly rotating neutron stars to Kerr black holes. The initial stellar models are modeled as relativistic polytropes which are either secularly or dynamically unstable and with angular velocities which range from slow rotation to the mass-shedding limit. We investigate the gravitational collapse by carefully studying not only the dynamics of the matter, but also that of the trapped surfaces, i.e., of both the apparent and event horizons formed during the collapse. The use of these surfaces, together with the dynamical horizon framework, allows for a precise measurement of the black-hole mass and spin. The ability to successfully perform these simulations for sufficiently long times relies on excising a region of the computational domain which includes the singularity and is within the apparent horizon. The dynamics of the collapsing matter is strongly influenced by the initial amount of angular momentum in the progenitor star and, for initial models with sufficiently high angular velocities, the collapse can lead to the formation of an unstable disc in differential rotation. All of the simulations performed with uniformly rotating initial data and a polytropic or ideal-fluid equation of state show no evidence of shocks or of the presence of matter on stable orbits outside the black hole.

The aim of this paper is to study the time delay on electromagnetic signals propagating across a binary stellar system. We focus on the antisymmetric gravitomagnetic contribution due to the angular momentum of one of the stars of the pair. Considering a pulsar as the source of the signals, the effect would be manifest both in the arrival times of the pulses and in the frequency shift of their Fourier spectra. We derive the appropriate formulas and we discuss the influence of different configurations on the observability of gravitomagnetic effects. We argue that the recently discovered PSR J0737-3039 binary system does not permit the detection of the effects because of the large size of the eclipsed region.

We report on three numerical experiments on the implementation of Time-Delay Interferometry (TDI) for LISA, performed with Synthetic LISA, a C++/Python package that we developed to simulate the LISA science process at the level of scientific and technical requirements. Specifically, we study the laser-noise residuals left by first-generation TDI when the LISA armlengths have a realistic time dependence; we characterize the armlength-measurement accuracies that are needed to have effective laser-noise cancellation in both first- and second-generation TDI; and we estimate the quantization and telemetry bitdepth needed for the phase measurements. Synthetic LISA generates synthetic time series of the LISA fundamental noises, as filtered through all the TDI observables; it also provides a streamlined module to compute the TDI responses to gravitational waves according to a full model of TDI, including the motion of the LISA array and the temporal and directional dependence of the armlengths. We discuss the theoretical model that underlies the simulation, its implementation, and its use in future investigations on system-characterization and data-analysis prototyping for LISA.

We study the fermionic couplings of the neutral Higgs bosons in the two Higgs doublet model, assuming a four-texture structure for the Yukawa matrices. We then derive the low-energy constraints on the model, focusing in $b$-quark and lepton physics, and apply them to study Higgs boson detection at future colliders. We show that the bound on the flavor-violating parameter ${\chi }_{sb}$ obtained from the contribution due to the $b\overline{s}{h}^0$ coupling to the decay $b\to s+\gamma$ (roughly of the order ${10}^{-1}–{10}^{-2}$) is approximately a factor 10 more restrictive than that obtained from the current bound on $\Gamma (B_s^0\to {\mu }^{-}{\mu }^{+})$ (which gives a bound on ${\chi }_{sb}$ of the order ${10}^0–{10}^{-1}$). On the other hand, the analysis of the LFV decay $\mu \to e\gamma$ leads to the constraint ${\chi }_{\mu \tau }\lesssim {10}^{-2}$. The observation of a Higgs signal at a future muon collider would confirm the results of these constraints for $\tan \beta \lesssim 15$, while for larger values of $\tan \beta$ such colliders will not improve the bounds derived from low-energy data. At a hadron collider it is further possible to study the Higgs boson coupling $h^{0}b\overline{b}$ by searching for the associated production of the Higgs boson with $b\overline{b}$ pairs.

We evaluate the static $qq\overline{q}\overline{q}$ and $qqqq\overline{q}$ potentials in the quenched theory at $\beta =5.8$ and $\beta =6.0$ on a lattice of size ${16}^3\times 32$. We compare the static potentials to the sum of two meson potentials for the tetraquark system and to the sum of the baryonic and mesonic potentials for the pentaquark state, as well as, with the confining potential obtained in the strong coupling expansion.

We propose a new dynamical mechanism for spin asymmetries in semi-inclusive deep inelastic scattering, utilizing strong vacuum fluctuations of the gluon field described semiclassically by instantons. Those can generate large asymmetry because they can simultaneously generate (i) a chirality flip of the struck quark; (ii) large O(1) $T$-odd phase due to its final state interaction. The absolute magnitude of the effect is estimated using known parameters of the instanton ensemble in the QCD vacuum and known structure and fragmentation functions, without any new free parameters. The result agrees in sign and (roughly) in magnitude with the available data on single particle inclusive DIS. Furthermore, our predictions uniquely relate effects for longitudinally and transversely polarized targets.

Recent data of two-body nonleptonic $B$ meson decays allow a topological-amplitude analysis up to the $O({\lambda }^2)$ accuracy, where $\lambda$ denotes the Wolfenstein parameter. We find an exact solution from the $B\to \pi \pi$ data and an exact solution from the $B\to K\pi$ data, which satisfy the approximate SU(3) flavor symmetry. These solutions indicate that the color-suppressed tree amplitude is large, all other amplitudes can be understood within the standard-model, and the weak phases ${\varphi }_2\approx {90}^o$ and ${\varphi }_3\approx {60}^o$ are consistent with the global unitarity triangle fit.

We study the decay mode of the top quark decaying into $Wb$ in the topcolor-assisted technicolor (TC2) model where the top quark is distinguished from other fermions by participating in a strong interaction. We find that the TC2 correction to the decay width $\Gamma (t\to bW)$ is generally several percent and the maximum value can reach 8% for the currently allowed parameters. The magnitude of such a correction is comparable with the QCD correction and larger than that of the minimal supersymmetric model. Such a correction might be observable in the future colliders. We also study the TC2 correction to the branching ratio of top quark decay into the polarized $W$ bosons and find the correction is below 1%. After considering the TC2 correction, we find that our theoretical predictions about the decay branching ratio are also consistent with the experimental data.

Soft supersymmetry breaking terms involving heavy singlet sneutrinos can be the dominant source of leptogenesis. The relevant range of parameters is different from standard leptogenesis: a lighter Majorana mass, $M\lesssim {10}^9\mathrm{G}\mathrm{e}\mathrm{V}$ (allowing a solution of the gravitino problem), and smaller Yukawa couplings, $Y_N\lesssim {10}^{-4}$. We investigate whether the various couplings of the singlet sneutrinos, which are constrained by the requirement of successful “soft leptogenesis,” can have observable phenomenological consequences. Specifically, we calculate the contributions of the relevant soft supersymmetric breaking terms to the electric dipole moments of the charged leptons and to lepton flavor violating decays. Our result is that these contributions are small.

There is much discussion of scenarios where the space-time coordinates $x^{\mu }$ are noncommutative. The discussion has been extended to include nontrivial anticommutation relations among spinor coordinates in superspace. A number of authors have studied field theoretical consequences of the deformation of $\mathcal{N}=1$ superspace arising from nonanticommutativity of coordinates $\theta$, while leaving $\overline{\theta }$’s anticommuting. This is possible in Euclidean superspace only. In this note we present a way to extend the discussion by making both $\theta$ and $\overline{\theta }$ coordinates nonanticommuting in Minkowski superspace. We present a consistent algebra for the supercoordinates, find a star-product, and give the Wess-Zumino Lagrangian ${\mathcal{L}}_{WZ}$ within our model. It has two extra terms due to non(anti)commutativity. The Lagrangian in Minkowski superspace is always manifestly Hermitian and for ${\mathcal{L}}_{WZ}$ it preserves Lorentz invariance.

We study the Klein-Gordon equation for a massive scalar field in Kerr spacetime in the time-domain. We demonstrate that under conditions of super-radiance, the scalar field becomes unstable and its amplitude grows without bound. We also estimate the growth rate of this instability.

We present supergravity solutions for $1/8$-supersymmetric black supertubes with three charges and three dipoles. Their reduction to five dimensions yields supersymmetric black rings with regular horizons and two independent angular momenta. The general solution contains seven independent parameters and provides the first example of nonuniqueness of supersymmetric black holes. In ten dimensions, the solutions can be realized as D1-D5-P black supertubes. We also present a worldvolume construction of a supertube that exhibits three dipoles explicitly. This description allows an arbitrary cross section but captures only one of the angular momenta.

Dark energy candidates for which the equation-of-state parameter $w$ is less than $-1$ violate the dominant energy condition, and are typically unstable. In scalar-tensor theories of gravity, however, the expansion of the universe can mimic the behavior of general relativity with $w<-1$ dark energy, without violating any energy conditions. We examine whether this possibility is phenomenologically viable by studying Brans-Dicke models and characterizing both the naturalness of the models themselves, and additional observational constraints from limits on the time-dependence of Newton’s constant. We find that only highly contrived models would lead observers to measure $w<-1$.