In this work, we study the effects of breaking Lorentz symmetry in scalar-tensor theories of gravity taking torsion into account. We show that a space-time with torsion interacting with a Maxwell field by means of a Chern-Simons-like term is able to explain the optical activity in synchrotron radiation emitted by cosmological distant radio sources. Without specifying the source of the dilaton-gravity, we study the dilaton-solution. We analyze the physical implications of this result in the Jordan-Fierz frame. We also analyze the effects of the Lorentz-breaking in the cosmic string formation process. We obtain the solution corresponding to a cosmic string in the presence of torsion by keeping track of the effects of the Chern-Simons coupling and calculate the charge induced on this cosmic string in this framework. We also show that the resulting charged cosmic string yields important effects concerning the background radiation. The optical activity in this case is also worked out and discussed.

We derive a tidal potential for a self-gravitating fluid star orbiting a Kerr black hole along a timelike geodesic, extending previous works by Fishbone and Marck. In this paper, the tidal potential is calculated up to the third- and fourth-order terms in $R/r$, where $R$ is the stellar radius and $r$ the orbital separation, in the Fermi normal coordinate system following the framework developed by Manasse and Misner. The new formulation is applied for determining the tidal disruption limit (Roche limit) of corotating Newtonian stars in circular orbits moving on the equatorial plane of Kerr black holes. It is demonstrated that the third- and fourth-order terms quantitatively play an important role in the Roche limit for close orbits with $R/r\gtrsim 0.1$. It is also indicated that the Roche limit of neutron stars orbiting a stellar-mass black hole near the innermost stable circular orbit may depend sensitively on the equation of state of the neutron star.

We present a double distribution function of dark matter halos, with respect to both object mass and local over- (or under-) density. This analytical tool provides a statistical treatment of the properties of matter surrounding collapsed objects, and can be used to study environmental effects on hierarchical structure formation. The size of the “local environment” of a collapsed object is defined to depend on the mass of the object. The Press-Schechter mass function is recovered by integration of our double distribution over the density contrast. We also present a detailed treatment of the evolution of overdensities and underdensities in ${\Omega }_{\mathrm{m}}+{\Omega }_{\Lambda }=1$ and ${\Omega }_{\mathrm{m}}=1$ universes according to the spherical evolution model. We explicitly distinguish between true and linearly extrapolated overdensities and provide conversion relations between the two quantities.

Recent theoretical ideas and observational claims suggest that the fine structure constant $\alpha$ may be variable. We examine a spectrum of models in which $\alpha$ is a function of a scalar field. Specifically, we consider three scenarios: oscillating $\alpha$, monotonic time variation of $\alpha$, and time-independent $\alpha$ that is spatially varying. We examine the constraints imposed upon these theories by cosmological observations, particle detector experiments, and “fifth force” experiments. These constraints are very strong on models involving oscillation but cannot compete with bounds from the Oklo subnuclear reactor on models with monotonic timelike variation of $\alpha$. One particular model with spatial variation is consistent with all current experimental and observational measurements, including those from two seemingly conflicting measurements of the fine structure constant using the many multiplet method on absorption lines.

We study the evolution of cosmological perturbations, using a hybrid approximation scheme which upgrades the weak-field limit of Einstein’s field equations to account for post-Newtonian scalar and vector metric perturbations and for leading-order source terms of gravitational waves, while including also the first- and second-order perturbative approximations. Our equations, which are derived in the Poisson gauge, provide a unified description of matter inhomogeneities in a Universe filled with a pressureless and irrotational fluid and a cosmological constant, ranging from the linear to the highly nonlinear regime. The derived expressions for scalar, vector and tensor modes may have a wide range of cosmological applications, including secondary CMB anisotropy and polarization effects, cosmographic relations in a inhomogeneous Universe, gravitational lensing and the stochastic gravitational-wave backgrounds generated by nonlinear cosmic structures.

Measurements of the linear power spectrum of galaxies have placed tight constraints on neutrino masses. We extend the framework of the halo model of cosmological nonlinear matter clustering to include the effect of massive neutrino infall into cold dark matter (CDM) halos. The magnitude of the effect of neutrino clustering for three degenerate mass neutrinos with $m_{{\nu }_i}=0.9\mathrm{e}\mathrm{V}$ is of order $\sim 1\%$, within the potential sensitivity of upcoming weak lensing surveys. In order to use these measurements to further constrain—or eventually detect—neutrino masses, accurate theoretical predictions of the nonlinear power spectrum in the presence of massive neutrinos will be needed, likely only possible through high-resolution multiple particle (neutrino, CDM and baryon) simulations.

The statistical association between the output of the Gravitational Wave (GW) detectors EXPLORER and NAUTILUS and a list of Gamma Ray Bursts (GRBs) detected by the satellite experiments BATSE and BeppoSAX has been analyzed using cumulative algorithms. GW detector data collected between 1991 and 1999 have been searched for an energy excess in a 10 s interval around the GRB flux peak times. The cumulative analysis of the data relative to a large number of GRBs (387) allows to push the upper bound for the corresponding GW burst amplitude down to $h=2.5\times {10}^{-19}$.

We make a detailed analysis of gauge-coupling unification in supersymmetry. When the standard model gauge group is embedded in a grand unified theory (GUT), new particles often appear below the GUT scale in order to predict the right phenomenology at low-energy. While these new particles are beyond the reach of accelerator experiments, they change the prediction of ${\alpha }_s$. Here we classify all the $\mathbf{(}\mathrm{S}\mathrm{U}(3{)}_{\mathrm{C}},\mathrm{S}\mathrm{U}(2{)}_{\mathrm{L}}{\mathbf{)}}_{\mathrm{U}(1{)}_{\mathrm{Y}}}$ representations which improve or worsen the prediction. Running experimentally determined values of the coupling constants at two loops we calculate the allowed range of masses of fields in these representations. We explore the implication of these results in SU(5) and $\mathrm{S}\mathrm{U}(3{)}^3$ (trinification) models. We discover that minimal trinification predicts light triplet Higgs particles which lead to proton decay with a lifetime in the vicinity of the current experimental bound.

Using smearing of equilibrium lattice fields generated at finite temperature in the confined phase of $SU(2)$ lattice gauge theory, we have investigated the emerging topological objects (clusters of topological charge). Analyzing their monopole content according to the Polyakov gauge and the maximally Abelian gauge, we characterize part of them to correspond to nonstatic calorons or static dyons in the context of Kraan-van Baal caloron solutions with nontrivial holonomy. The behavior of the Polyakov loop inside these clusters and the (model-dependent) topological charges of these objects support this interpretation.

We report on a study of QCD thermodynamics with three flavors of quarks, using a Symanzik improved gauge action and the Asqtad $O(a^2)$ improved staggered quark action. Simulations were carried out with lattice spacings $1/4T$, $1/6T$, and $1/8T$ both for three degenerate quarks with masses less than or equal to the strange quark mass $m_s$ and for degenerate up and down quarks with masses in the range $0.1m_s\le m_{u,d}\le 0.6m_s$ and the strange quark mass fixed near its physical value. We present results for standard thermodynamics quantities, such as the Polyakov loop, the chiral order parameter and its susceptibility. For the quark masses studied to date we find a rapid crossover rather than a bona fide phase transition. We have carried out the first calculations of quark number susceptibilities with three flavors of sea quarks. These quantities are of physical interest because they are related to event-by-event fluctuations in heavy ion collision experiments. Comparison of susceptibilities at different lattice spacings show that our results are close to the continuum values.

The recently reported ${\Theta }^{+}(1540)$ exotic baryon seems to be very narrow: $\Gamma (\Theta )<1\mathrm{M}\mathrm{e}\mathrm{V}$ according to some analyses. Using methods of low energy scattering theory, we develop expectations for the width of the $\Theta$, an elastic resonance in $KN$ scattering in a theory where the characteristic range of interactions is $\sim 1\mathrm{F}\mathrm{e}\mathrm{r}\mathrm{m}\mathrm{i}$. If the $\Theta$ is a potential scattering resonance, generated by the forces in the $KN$ channel, its width is hard to account for unless the $KN$-channel orbital angular momentum is two or greater. If the $\Theta$ is generated by dynamics in a confined channel, its coupling to the scattering channel is at least an order of magnitude less than the coupling of the $\Lambda (1520)$ unless $\ell \ge 2$. Either way, if the $\Theta$ proves to be in the $KN$ $s$- or $p$-wave, new physics must be responsible for its narrow width.

The unpolarized spin-flip isoscalar generalized parton distribution function $(E^u+E^d)(x,\xi ,t)$ is studied in the large-$N_c$ limit at a low normalization point in the framework of the chiral quark-soliton model. This is the first study of generalized parton distribution functions in this model, which appear only at the subleading order in the large-$N_c$ limit. Particular emphasis is put therefore on the demonstration of the theoretical consistency of the approach. The forward limit of $(E^u+E^d)(x,\xi ,t)$ of which only the first moment–the anomalous isoscalar magnetic moment of the nucleon–is known phenomenologically, is computed numerically. Observables sensitive to $(E^u+E^d)(x,\xi ,t)$ are discussed.

In this paper we present an analytic result for the evolution in $Q^2$ of the structure functions for the neutrino-nucleon interaction, valid at twist-2 in the region of small values of the Bjorken $x$ variable and for soft nonperturbative input. In the special case of flat initial conditions, we include in the calculation also the contribution of the twist-4 gluon recombination corrections, whose effect in the evolution is explicitly determined. Finally, we estimate the resulting charged-current neutrino-nucleon total cross section and discuss its behavior at ultrahigh energies.

Using the novel diagrammatic rules recently proposed by Cachazo, Svrcek, and Witten, I give a compact, manifestly Lorentz-invariant form for tree-level gauge-theory amplitudes with three opposite helicities.

By using suitably improved surface integrals, we give a unified geometric derivation of the generalized Smarr relation for higher dimensional Kerr black holes which is valid both in flat and in anti-de Sitter backgrounds. The improvement of the surface integrals, which allows one to use them simultaneously at infinity and on the horizon, consists in integrating them along a path in solution space. Path independence of the improved charges is explicitly proved. It is also shown that the charges for higher dimensional Kerr-AdS black holes can be correctly computed from the standard Hamiltonian or Lagrangian surface integrals.

We study the possibility of a first-order electroweak phase transition due to a dimension-six operator in the effective Higgs potential. In contrast with previous attempts to make the electroweak phase transition strongly first-order as required by electroweak baryogenesis, we do not rely on large one-loop thermally generated cubic Higgs interactions. Instead, we augment the standard model effective theory with a dimension-six Higgs operator. This addition enables a strong first-order phase transition to develop even with a Higgs boson mass well above the current direct limit of 114 GeV. The ${\phi }^6$ term can be generated for instance by strong dynamics at the TeV scale or by integrating out heavy particles like an additional singlet scalar field. We discuss conditions to comply with electroweak precision constraints, and point out how future experimental measurements of the Higgs self-couplings could test the idea.

We consider an extension of the standard model gauge symmetry to a local gauge group $\mathrm{S}\mathrm{U}(3{)}_C\otimes \mathrm{S}\mathrm{U}(3{)}_L\otimes \mathrm{U}(1{)}_X$ which is a subgroup of $\mathrm{S}\mathrm{U}(4{)}_{\mathrm{P}\mathrm{S}}\otimes \mathrm{S}\mathrm{U}(4{)}_{L+R}$. The symmetry breaking pattern is $\mathrm{S}\mathrm{U}(4)\to \mathrm{S}\mathrm{U}(3)\otimes \mathrm{U}(1)$ for both weak $\mathrm{S}\mathrm{U}(4{)}_{L+R}$ and strong Pati-Salam $\mathrm{S}\mathrm{U}(4{)}_{\mathrm{P}\mathrm{S}}$ group. The $\mathrm{S}\mathrm{U}(3{)}_C\otimes \mathrm{U}(1{)}_{B-L}\otimes \mathrm{S}\mathrm{U}(3{)}_L\otimes \mathrm{U}(1{)}_{Y1}$ (3-3-1-1) local gauge symmetry breaks to $\mathrm{S}\mathrm{U}(3{)}_C\otimes \mathrm{S}\mathrm{U}(3{)}_L\otimes \mathrm{U}(1{)}_X$ and generates a 3-3-1 model with three-generation, anomaly-free fermions which transform as bifundamentals of (3-3-1-1). The 3-3-1 model is of Pleitez-Frampton type but $\mathrm{S}\mathrm{U}(3{)}_L$ gauge bosons ($B-L=0$) do not include bilepton gauge boson. The neutral gauge bosons include $\gamma ,Z,Z^{\prime }$ and a fourth, heavy gauge boson $Z^{\prime \prime }$ which decouples from rest but can decay to ordinary fermions. An analysis for two-body decays of neutral $Z^{\prime }$ gauge boson is presented. From Yukawa interactions, the masses of all exotic fermions are obtained in the TeV region. This restricts $Z^{\prime }$ decays to exotic fermions. The $Z^{\prime }$ is also found to be leptophobic and decays mainly to quarks.

We propose a new mass reconstruction technique for SUSY processes at the LHC. The idea is to completely solve the kinematics of the SUSY cascade decay by using the assumption that the selected events satisfy the same mass shell conditions of the sparticles involved in the cascade decay. Using this technique, we study the measurement of the mass of the bottom squarks in the cascade decay of the gluino. Based on the final state including two high $p_T$ leptons and two $b$-jets, we investigate different possible approaches to the mass reconstruction of the gluino and the two bottom squarks. In particular, we evaluate the performance of different algorithms in discriminating two bottom squark states with a mass difference as low as 5%.

We search for a charged partner of the $X(3872)$ in the decay $B\to X^{-}K$, $X^{-}\to J/\psi {\pi }^{-}{\pi }^0$, using $234\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}(4S)$ resonance with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ asymmetric-energy storage ring. The resulting product branching fraction upper limits are $\mathcal{B}(B^0\to X^{-}{K}^{+},X^{-}\to J/\psi {\pi }^{-}{\pi }^0)<5.4\times {10}^{-6}$ and $\mathcal{B}(B^{-}\to X^{-}{\overline{K}}^0,X^{-}\to J/\psi {\pi }^{-}{\pi }^0)<22\times {10}^{-6}$ at the $90\%$ confidence level.

Using the Frobenius method, we find high overtones of the Dirac quasinormal spectrum for the Schwarzschild black hole. At high overtones, the spacing for imaginary part of ${\omega }_n$ is equidistant and equals to $\mathrm{I}\mathrm{m}({\omega }_{n+1})-\mathrm{I}\mathrm{m}({\omega }_n)=i/8M$, $M$ being the black hole mass, which is twice less than that for fields of integer spin. At high overtones, the real part of ${\omega }_n$ goes to zero. This supports the suggestion that the expected correspondence between quasinormal modes and Barbero-Immirzi parameter in Loop Quantum Gravity is just a numerical coincidence.