We present the results of a search for new particles that lead to a $Z$ boson plus jets in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using the Collider Detector at Fermilab (CDF II). A data sample with a luminosity of $1.06{\mathrm{fb}}^{-1}$ collected using $Z$ boson decays to $ee$ and $\mu \mu$ is used. We describe a completely data-based method to predict the dominant background from standard model $Z+\mathrm{\text{jet}}$ events. This method can be similarly applied to other analyses requiring background predictions in multijet environments, as shown when validating the method by predicting the background from $W+\mathrm{\text{jets}}$ in $t\overline{t}$ production. No significant excess above the background prediction is observed, and a limit is set using a fourth generation quark model to quantify the acceptance. Assuming $\mathrm{BR}(b^{\prime }\to bZ)=100\%$ and using a leading-order calculation of the $b^{\prime }$ cross section, $b^{\prime }$ quark masses below $268\mathrm{GeV}/c^2$ are excluded at 95% confidence level.

We revisit the issue of a correlation between the atomic hydrogen gas in our local galaxy and the cosmic microwave background, a detection of which has been claimed in some literature. We cross correlate the 21-cm emission of galactic atomic hydrogen as traced by the Leiden/Argentine/Bonn Galactic Hi survey with the 3-year cosmic microwave background data from the Wilkinson microwave anisotropy probe. We consider a number of angular scales, masks, and Hi velocity slices and find no statistically significant correlation.

In the context of the AdS/CFT correspondence we calculate the induced stress tensor of static dipoles (electric-electric and electric-magnetic) in a strongly coupled $\mathcal{N}=4$ SYM gauge theory, by solving the linearized Einstein equation with Maldecena string as a source. Analytic expressions are given for the far-field and a near-field close to one charge, and compared to what one has in weak coupling. The result can be compared to lattice results for QCD-like theories in a deconfined but strongly coupled regime.

We can understand many recently discovered features of flavor evolution in dense, self-coupled supernova neutrino and antineutrino systems with a simple, physical scheme consisting of two quasistatic solutions. One solution closely resembles the conventional, adiabatic single-neutrino Mikheyev-Smirnov-Wolfenstein (MSW) mechanism, in that neutrinos and antineutrinos remain in mass eigenstates as they evolve in flavor space. The other solution is analogous to the regular precession of a gyroscopic pendulum in flavor space, and has been discussed extensively in recent works. Results of recent numerical studies are best explained with combinations of these solutions in the following general scenario: (1) Near the neutrino sphere, the MSW-like many-body solution obtains. (2) Depending on neutrino vacuum mixing parameters, luminosities, energy spectra, and the matter density profile, collective flavor transformation in the nutation mode develops and drives neutrinos away from the MSW-like evolution and toward regular precession. (3) Neutrino and antineutrino flavors roughly evolve according to the regular precession solution until neutrino densities are low. In the late stage of the precession solution, a stepwise swapping develops in the energy spectra of ${\nu }_e$ and ${\nu }_{\mu }/{\nu }_{\tau }$. We also discuss some subtle points regarding adiabaticity in flavor transformation in dense-neutrino systems.

We calculate generating functions for a number of $U(N)$ $(SU(N))$ singlets in Fock space in several space dimensions. The motivation to find the explicit form of the functions is from the numerical approach applied to supersymmetric Yang-Mills quantum mechanics, based on Fock space. Incidentally the functions give many important insights into the quantum mechanical models based on $U(N)(SU(N))$ gauge group.

We derive the complete spectrum of gravitational waves induced by primordial scalar perturbations ranging over all observable wavelengths. This scalar-induced contribution can be computed directly from the observed scalar perturbations and general relativity and is, in this sense, independent of the cosmological model for generating the perturbations. The spectrum is scale invariant on small scales, but has an interesting scale dependence on large and intermediate scales, where scalar-induced gravitational waves do not redshift and are hence enhanced relative to the background density of the Universe. This contribution to the tensor spectrum is significantly different in form from the direct model-dependent primordial tensor spectrum and, although small in magnitude, it dominates the primordial signal for some cosmological models. We confirm our analytical results by direct numerical integration of the equations of motion.

We find the quasinormal modes of the charged scalar and Dirac fields in the background of the rotating charged black holes, described by the Kerr-Newman-de Sitter solution. The dependence of the quasinormal spectrum upon the black hole parameters mass $M$, angular momentum $a$, charge $Q$, as well as on values of the $\Lambda$-term and a field charge $q$ is investigated. Special attention is given to the near extremal limit of the black hole charge. In particular, we find that for both scalar and Dirac fields, charged perturbations decay quicker for $q>0$ and slower for $q<0$ for values of black holes charge $Q$ less than some threshold value, which is close to the extremal value of charge and depend on parameters of the black holes.

We perform axisymmetric simulations of the magnetorotational collapse of very massive stars in full general relativity. Our simulations are applicable to the collapse of supermassive stars with masses $M\gtrsim {10}^3{M}_{\odot }$ and to very massive Population III stars. We model our initial configurations by $n=3$ polytropes, uniformly rotating near the mass-shedding limit and at the onset of radial instability to collapse. The ratio of magnetic to rotational kinetic energy in these configurations is chosen to be small (1% and 10%). We find that such magnetic fields do not affect the initial collapse significantly. The core collapses to a black hole, after which black-hole excision is employed to continue the evolution long enough for the hole to reach a quasistationary state. We find that the black-hole mass is $M_h=0.95M$ and its spin parameter is $J_h/M_h^2=0.7$, with the remaining matter forming a torus around the black hole. The subsequent evolution of the torus depends on the strength of the magnetic field. We freeze the spacetime metric (“Cowling approximation”) and continue to follow the evolution of the torus after the black hole has relaxed to quasistationary equilibrium. In the absence of magnetic fields, the torus settles down following ejection of a small amount of matter due to shock heating. When magnetic fields are present, the field lines gradually collimate along the hole’s rotation axis. MHD shocks and the magnetorotational instability generate MHD turbulence in the torus and stochastic accretion onto the central black hole. When the magnetic field is strong, a wind is generated in the torus, and the torus undergoes radial oscillations that drive episodic accretion onto the hole. These oscillations produce long-wavelength gravitational waves potentially detectable by the Laser Interferometer Space Antenna. The final state of the magnetorotational collapse always consists of a central black hole surrounded by a collimated magnetic field and a hot, thick accretion torus. This system is a viable candidate for the central engine of a long-soft gamma-ray burst.

The periodic standing-wave method studies circular orbits of compact objects coupled to helically symmetric standing-wave gravitational fields. From this solution an approximation is extracted for the strong field, slowly inspiralling motion of black holes and binary stars. Previous work on this model has dealt with nonlinear scalar models, and with linearized general relativity. Here we present the results of the method for the post-Minkowski (PM) approximation to general relativity, the first step beyond linearized gravity. We compute the PM approximation in two ways: first, via the standard approach of computing linearized gravitational fields and constructing from them quadratic driving sources for second-order fields, and second, by solving the second-order equations as an “exact” nonlinear system. The results of these computations have two distinct applications: (i) The computational infrastructure for the exact PM solution will be directly applicable to full general relativity. (ii) The results will allow us to begin supplying initial data to collaborators running general relativistic evolution codes.

In homogeneous and isotropic loop quantum cosmology, gravity can behave repulsively at Planckian energy densities leading to the replacement of the big bang singularity with a big bounce. Yet in any bouncing scenario it is important to include nonlinear effects from anisotropies which typically grow during the collapsing phase. We investigate the dynamics of a Bianchi I anisotropic model within the framework of loop quantum cosmology. Using effective semiclassical equations of motion to study the dynamics, we show that the big bounce is still predicted with only differences in detail arising from the inclusion of anisotropies. We show that the anisotropic shear term grows during the collapsing phase, but remains finite through the bounce. Immediately following the bounce, the anisotropies decay and with the inclusion of matter with equation of state $w<+1$, the universe isotropizes in the expanding phase.

Exact solutions of traversable wormholes are found under the assumption of spherical symmetry and the existence of a nonstatic conformal symmetry, which presents a more systematic approach in searching for exact wormhole solutions. In this work, a wide variety of solutions are deduced by considering choices for the form function, a specific linear equation of state relating the energy density and the pressure anisotropy, and various phantom wormhole geometries are explored. A large class of solutions impose that the spatial distribution of the exotic matter is restricted to the throat neighborhood, with a cutoff of the stress-energy tensor at a finite junction interface, although asymptotically flat exact solutions are also found. Using the “volume integral quantifier,” it is found that the conformally symmetric phantom wormhole geometries may, in principle, be constructed by infinitesimally small amounts of averaged null energy condition violating matter. Considering the tidal acceleration traversability conditions for the phantom wormhole geometry, specific wormhole dimensions and the traversal velocity are also deduced.

We consider a braneworld model with bulk-brane energy exchange. This allows for crossing of the $w=-1$ phantom divide line without introducing phantom energy with quantum instabilities. We use the latest SnIa data included in the Gold06 data set to provide an estimate of the preferred parameter values of this braneworld model. We use three fitting approaches which provide best-fit parameter values and hint towards a bulk energy component that behaves like relativistic matter which is propagating in the bulk and is moving at a speed $v$ along the fifth dimension, while the bulk-brane energy exchange component corresponds to negative pressure and signifies energy flowing from the bulk into the brane. We find that the best-fit effective equation of state parameter $w_{\mathrm{eff}}$ marginally crosses the phantom divide line $w=-1$. Thus, we have demonstrated both the ability of this class of braneworld models to provide crossing of the phantom divide and also that cosmological data hint towards natural values for the model parameters.

In order to shed some light on the current discussion about $f(R)$-gravity theories we derive and discuss the bounds imposed by the energy conditions on a general $f(R)$ functional form. The null and strong energy conditions in this framework are derived from Raychaudhuri’s equation along with the requirement that gravity is attractive, whereas the weak and dominant energy conditions are stated from a comparison with the energy conditions that can be obtained in a direct approach via an effective energy-momentum tensor for $f(R)$ gravity. As a concrete application of the energy conditions to locally homogeneous and isotropic $f(R)$ cosmology, the recent estimated values of the deceleration and jerk parameters are used to examine the bounds from the weak energy condition on the parameters of two families of $f(R)$-gravity theories.

At redshifts $z\gtrsim 30$ neutral hydrogen gas absorbs cosmic microwave background radiation at the 21 cm spin-flip frequency. In principle this is observable and a high-precision probe of cosmology. We calculate the linear-theory angular-power spectrum of this signal and cross correlation between redshifts on scales much larger than the linewidth. In addition to the well-known redshift distortion and density perturbation sources, a full linear analysis gives additional contributions to the power spectrum. On small scales there is a percent-level linear effect due to perturbations in the 21 cm optical depth, and perturbed recombination modifies the gas temperature perturbation evolution (and hence spin temperature and 21 cm power spectrum). On large scales there are several post-Newtonian and velocity effects; although negligible on small scales, these additional terms can be significant at $l\lesssim 100$ and can be nonzero even when there is no background signal. We also discuss the linear effect of reionization rescattering, which damps the entire spectrum and gives a very small polarization signal on large scales. On small scales we also model the significant nonlinear effects of evolution and gravitational lensing. We include full results for numerical calculation and also various approximate analytic results for the power spectrum and evolution of small-scale perturbations.

The greatest challenge in the interpretation of galaxy clustering data from any surveys is galaxy bias. Using a simple Fisher matrix analysis, we show that the bispectrum provides an excellent determination of linear and nonlinear bias parameters of intermediate and high-$z$ galaxies, when all measurable triangle configurations down to mildly nonlinear scales, where perturbation theory is still valid, are included. The bispectrum is also a powerful probe of primordial non-Gaussianity. The planned galaxy surveys at $z\gtrsim 2$ should yield constraints on non-Gaussian parameters, $f_{NL}^{\mathrm{loc}.}$ and $f_{NL}^{\mathrm{eq}.}$, that are comparable to, or even better than, those from cosmic microwave background experiments. We study how these constraints improve with volume and redshift range, as well as the number density of galaxies. Finally, we show that a halo occupation distribution may be used to improve these constraints further by lifting degeneracies between gravity, bias, and primordial non-Gaussianity.

In the experiment with the SND detector at the VEPP-2M $e^{+}{e}^{-}$ collider measuring the $e^{+}{e}^{-}\to \eta \gamma$ cross section in the energy range $0.6<\sqrt{s}<1.38\mathrm{GeV}$ the reanalysis of data is performed. The goal is to improve the accuracy of the previous results by analyzing ambiguities in the approximation of energy dependence of the $e^{+}{e}^{-}\to \eta \gamma$ cross section, which were not taken into account in our previous study. We report new results on the approximation of the $e^{+}{e}^{-}\to \eta \gamma$ cross section based on the vector dominance model under new model parameter assumptions.

Scale invariance may be a classical symmetry which is broken radiatively. This provides a simple way to stabilize the scale of electroweak symmetry breaking against radiative corrections. The simplest phenomenologically successful model of this type involves the addition of one real scalar field to the standard model. In this minimal model the electroweak Higgs can be interpreted as the pseudo-Goldstone boson of broken scale invariance. We study the possible origin of neutrino mass in such models, both at tree-level and radiatively.

We study the pair production of doubly charged Higgs bosons at the CERN Large Hadron Collider (LHC), assuming the doubly charged Higgs to be part of an $\mathrm{SU}(2{)}_L$ triplet which generates Majorana masses for left-handed neutrinos. Such pair production has the advantage that it is not constrained by the triplet vacuum expectation value, which tends to make the single production rate rather small. We point out that, in addition to the Drell-Yan production mechanism, two-photon processes also contribute to $H^{++}{H}^{--}$ production at a level comparable to the QCD corrections to the Drell-Yan channel. Decays of the doubly charged Higgs into both the ${\ell }^{+}{\ell }^{+}$ and $W^{+}{W}^{+}$ modes are studied in detail to optimize the signal observation over the backgrounds. Doubly charged scalars should be observable at the LHC with $300{\mathrm{fb}}^{-1}$ integrated luminosity in the ${\ell }^{\pm }{\ell }^{\pm }$ channel up to the mass range of 1 TeV even with a branching fraction of about 60%, and in the $W^{\pm }{W}^{\pm }$ channel up to a mass of 700 GeV. Such a doubly charged Higgs, if it is a member of a triplet that generates neutrino masses, cannot be long-lived on the scale of collider detectors although it might lead to a displaced secondary vertex during its decay if it is lighter than about 250 GeV.

We extend previous analyses of the supersymmetric loop correction to the neutral Higgs couplings to include the coupling ${\chi }_j^{+}{\chi }_k^{-}{H}_l^0$. The analysis completes the previous analyses where similar corrections were computed for the $\overline{\tau }\tau H_l^0$, $\overline{b}b{H}_l^0$, $\overline{c}c{H}_l^0$ and for $\overline{t}t{H}_l^0$ couplings within the minimal supersymmetric standard model. The effective one-loop Lagrangian is then applied to the computation of the neutral Higgs decays. The sizes of the supersymmetric loop corrections of the neutral Higgs decay widths into ${\chi }_i^{+}{\chi }_j^{-}$ ($i=1$, 2; $j=1$, 2) are investigated and the supersymmetric loop correction is found to be in the range of $7\sim 15\%$ in significant regions of the parameter space. By including the loop corrections of the other decay channels $\overline{b}b$, $\overline{t}t$, $\overline{\tau }\tau$, $\overline{c}c$, and ${\chi }_i^0{\chi }_j^0$ ($i=1–4$; $j=1–4$), the corrections to branching ratios for $H_l^0\to {\chi }_i^{+}{\chi }_j^{-}$ can reach as high as 40%. The effects of $CP$ phases on the branching ratio are also investigated.

We investigate the possibility of electroweak phase transition in the minimal supersymmetric standard model with an extra $U(1{)}^{\prime }$. This model has two Higgs doublets and a singlet, in addition to a singlet exotic quark superfield. We find that at the one-loop level this model may accommodate the electroweak phase transitions that are strongly first order in a reasonably large region of the parameter space. In the parameter region where the phase transitions take place, we observe that the lightest scalar Higgs boson has a smaller mass when the strength of the phase transition becomes weaker. Also, the other three heavier neutral Higgs bosons get more large masses when the strength of the phase transition becomes weaker.