We show that the predicted primordial helium production is significantly reduced when new measurements of the neutron lifetime and the implied enhancement in the weak reaction rates are included in big-bang nucleosynthesis. Therefore, even if a narrow uncertainty in the observed helium abundance is adopted, this brings the constraint on the baryon-to-photon ratio from BBN and the observed helium into better accord with the independent determination of the baryon content deduced from the WMAP spectrum of power fluctuations in the cosmic microwave background and measurements of primordial deuterium in narrowline quasar absorption systems at high redshift.

The polarization plane of the cosmic microwave background radiation can be rotated either in a magnetized plasma or in the presence of a quintessential background with pseudoscalar coupling to electromagnetism. A unified treatment of these two phenomena is presented for cold and warm electron-ion plasmas at the prerecombination epoch. The electron temperature is only relevant to the relativistic correction of the cold plasma results. The spectrum of plasma excitations is obtained from a generalized Appleton-Hartree equation, describing simultaneously the high-frequency propagation of electromagnetic waves in a magnetized plasma with a dynamical quintessence field. It is shown that these two effects are comparable for the plausible range of parameters allowed by present constraints. It is then argued that the generalized expressions derived in the present study may be relevant for direct searches of a possible rotation of the cosmic microwave background polarization.

By assuming the existence of the sequential fourth generation to the minimal supersymmetric standard model (MSSM), we study the possibility of a strongly first-order electroweak phase transition. We find that there is a parameter region of the MSSM where the electroweak phase transition is strongly first order. In that parameter region, the mass of the lighter scalar Higgs boson is calculated to be above the experimental lower bound, and the scalar quarks of the third and the fourth generations are heavier than the corresponding quarks.

We consider a general formalism to compute inclusive polarized and unpolarized cross sections within pQCD and the factorization scheme, taking into account parton intrinsic motion in distribution and fragmentation functions, as well as in the elementary dynamics. Surprisingly, the intrinsic partonic motion, with all the correct azimuthal angular dependences, produces a strong suppression of the transverse single spin asymmetry arising from the Collins mechanism. As a consequence, and in contradiction with earlier claims, the Collins mechanism is unable to explain the large asymmetries found in $p^{\uparrow }p\to \pi X$ at moderate to large Feynman $x_F$. The Sivers effect is not suppressed.

We present the first investigation of the extrapolation of quenched nucleon magnetic moments in quenched chiral effective field theory. We utilize established techniques in finite-range regularization and incorporate finite-volume corrections to the relevant loop integrals. Finally, the contributions of dynamical sea quarks to the proton moment are estimated using a recently discovered phenomenological link between quenched and physical QCD.

Hadronic tau decay precision data are analyzed with account of both perturbative and power corrections of high orders within QCD. It is found that contributions of high order power corrections are essential for extracting a numerical value for the strange quark mass from the data on Cabibbo suppressed tau decays. We show that with inclusion of new five-loop perturbative corrections in the analysis the convergence of perturbation theory remains acceptable only for few low order moments. We obtain $m_s(M_{\tau })=130\pm 27\mathrm{M}\mathrm{e}\mathrm{V}$ in agreement with previous estimates.

It is by now established that neutrinos mix, have (different) nonzero masses, and therefore oscillate. The oscillation parameters themselves, however, are not all well-known. An open problem is that of the neutrino mass hierarchy. We study the possibility of determining the neutrino mass hierarchy with atmospheric neutrinos using an iron calorimeter detector capable of charge identification such as the proposed monolith and ical/ino detectors. We find that such detectors are sensitive to the sign of the mass-squared difference, ${\delta }_{32}=m_3^2-m_2^2$, provided the as-yet unknown mixing angle between the first and third generations, ${\theta }_{13}$, is greater than $6°$ (${sin}^{2}2{\theta }_{13}>0.04$). A result with a significance greater than $90\%$ CL requires large exposures (more than 500 kton-years) as well as good energy and angular resolution of the detected muons (better than $15\%$), especially for small ${\theta }_{13}$. Hence obtaining definitive results with such a detector is difficult, unless ${\theta }_{13}$ turns out to be large. In contrast, such detectors can establish a clear oscillation pattern in atmospheric neutrinos in about 150 kton-years, therefore determining the absolute value of ${\delta }_{32}$ and ${sin}^{2}2{\theta }_{23}$ to within $10\%$.

We start from a local and linear space-time relation between the electromagnetic excitation and the field strength. Then we study the generally covariant Fresnel surfaces for light rays and light waves. The metric and the connection of space-time are left unspecified. Accordingly, our framework is ideally suited for a search of possible violations of the Lorentz symmetry in the photon sector of the extended standard model. We discuss how the skewon part of the constitutive tensor, if suitably parametrized, influences the Fresnel surfaces and disturbs the light cones of vacuum electrodynamics. Conditions are specified that yield the reduction of the original quartic Fresnel surface to the double light cone structure (birefringence) and to the single light cone. Qualitatively, the effects of the real skewon field can be compared to those in absorbing material media. In contrast, the imaginary skewon field can be interpreted in terms of nonabsorbing media with natural optical activity and Faraday effects. The astrophysical data on gamma-ray bursts are used for deriving an upper limit for the magnitude of the skewon field.

We present a set of boundary conditions for solving the elliptic equations in the initial data problem for space-times containing a black hole, together with a number of constraints to be satisfied by the otherwise freely specifiable standard parameters of the conformal thin sandwich formulation. These conditions altogether are sufficient for the construction of a horizon that is instantaneously in equilibrium in the sense of the isolated horizons formalism. We then investigate the application of these conditions to the initial data problem of binary black holes and discuss the relation of our analysis with other proposals that exist in the literature.

Light propagation is investigated in the context of local anisotropic nonlinear dielectric media at rest with the dielectric coefficients $\epsilon ^{\mu }{}_{\nu }=\epsilon ^{\mu }{}_{\nu }(\overrightarrow{E},\overrightarrow{B})$ and constant $\mu$, in the limit of geometrical optics. Birefringence was examined and the general conditions for its occurrence were presented. A toy model is exhibited, in which uniaxial birefringent media with nonlinear dielectric properties could be driven by external fields in such way that birefringence may be artificially controlled. The effective geometry interpretation is also addressed.

We study some exact solutions in a $D(\ge 4)$-dimensional Einstein-Born-Infeld theory with a cosmological constant. These solutions are asymptotically de Sitter or anti-de Sitter, depending on the sign of the cosmological constant. Black hole horizon and cosmological horizon in these spacetimes can be a positive, zero or negative constant curvature hypersurface. We discuss the thermodynamics associated with black hole horizon and cosmological horizon. In particular we find that for the Born-Infeld black holes with Ricci flat or hyperbolic horizon in AdS space, they are always thermodynamically stable, and that for the case with a positive constant curvature, there is a critical value for the Born-Infeld parameter, above which the black hole is also always thermodynamically stable, and below which a unstable black hole phase appears. In addition, we show that although the Born-Infeld electrodynamics is nonlinear, both black hole horizon entropy and cosmological horizon entropy can be expressed in terms of the Cardy-Verlinde formula. We also find a factorized solution in the Einstein-Born-Infeld theory, which is a direct product of two constant curvature spaces: one is a two-dimensional de Sitter or anti-de Sitter space, the other is a ($D-2$)-dimensional positive, zero or negative constant curvature space.

We study analytically and numerically the evolution of bound systems in universes with accelerating expansion where the acceleration either increases with time towards a Big Rip singularity (phantom cosmologies) or decreases with time (quintessence). We confirm the finding of Caldwell et al. [R. R. Caldwell, M. Kamionkowski and N. N. Weinberg, Phys. Rev. Lett. 91, 071301 (2003).] that bound structures get dissociated in phantom cosmologies but we demonstrate that this happens earlier than anticipated in Ref. [R. R. Caldwell, M. Kamionkowski and N. N. Weinberg, Phys. Rev. Lett. 91, 071301 (2003).]. In particular we find that the “rip time” when a bound system gets unbounded is not the time when the repulsive phantom energy gravitational potential due to the average $(\rho +3p)$ balances the attractive gravitational potential of the mass M of the system. Instead, the “rip time” is the time when the minimum of the time-dependent effective potential (including the centrifugal term) disappears. For the Milky Way galaxy this happens approximately 180 Myrs before the Big Rip singularity instead of approximately 60 Myrs indicated in [R. R. Caldwell, M. Kamionkowski and N. N. Weinberg, Phys. Rev. Lett. 91, 071301 (2003).] for a phantom cosmology with $\mathrm{w}=-1.5$. A numerical reconstruction of the dissociating bound orbits is presented.

In the past few years, the Chaplygin gas has been considered as an appealing candidate for unifying dark matter and dark energy into a single substance. This picture had to face several problems when trying to fit its predictions with cosmological observations. We point out another potential problem of this model, showing that, when the Chaplygin gas is described through a classical scalar field, the corresponding trajectories are strongly unstable. This implies that an extreme fine-tuning must apply to the initial values of the field in order to end up today with values allowed by observational data.

We investigate the full $\mathrm{U}(3)\otimes \mathrm{U}(3)$ chiral symmetry restoration, at finite temperature and density, on the basis of a quark model which incorporates the most relevant properties of QCD in this context: explicit and spontaneous breaking of chiral symmetry and axial $U_A(1)$ symmetry breaking. A specific lattice-inspired behavior of the topological susceptibility, combined with the convergence of chiral partners, signals the onset of an effective chiral symmetry restoration. The results suggest that the axial part of the symmetry is restored before the possible restoration of the full $\mathrm{U}(3)\otimes \mathrm{U}(3)$ chiral symmetry can occur. This conclusion is valid in the context of both finite temperature and density.

We investigate a dynamical mass generation mechanism for the off-diagonal gluons and ghosts in $\mathrm{S}\mathrm{U}(N)$ Yang-Mills theories, quantized in the maximal Abelian gauge. Such a mass can be seen as evidence for the Abelian dominance in that gauge. It originates from the condensation of a mixed gluon-ghost operator of mass dimension two, which lowers the vacuum energy. We construct an effective potential for this operator by a combined use of the local composite operators technique with the algebraic renormalization and we discuss the gauge parameter independence of the results. We also show that it is possible to connect the vacuum energy, due to the mass dimension-two condensate discussed here, with the nontrivial vacuum energy originating from the condensate $⟨A_{\mu }^2⟩$, which has attracted much attention in the Landau gauge.

We study neutrino emission from a normal, ungapped, quark phase in the core of a compact star. Neutrino emission from noninteracting quark matter leads to an emissivity that scales as $ϵ\sim T^7$. We show that the emissivity is enhanced by a combination of Fermi liquid and non-Fermi liquid effects. Fermi liquid effects lead to an emissivity that scales as $ϵ\sim {\alpha }_s{T}^6$, as originally shown by Iwamoto. We demonstrate that non-Fermi liquid effects further enhance the rate, leading to $ϵ\sim {\alpha }_s^3{T}^6\log (m/T{)}^2$, where $m$ is the electric screening scale and $m\gg T$ under the conditions found in compact stars. We show, however, that combined with non-Fermi liquid effects in the specific heat the enhancement in the emissivity only leads to a modest reduction in the temperature of the star at late times. Our results confirm existing bounds on the presence of ungapped quark matter in compact stars. We also discuss neutrino emission from superconducting phases with ungapped fermionic excitations.

We construct a family of simple gauge models in which three sterile neutrinos become naturally light by virtue of a generalized seesaw mechanism involving a chiral gauge symmetry. Examples where the chiral gauge group is $\mathrm{S}\mathrm{U}(5{)}^{\prime }$, $\mathrm{S}\mathrm{U}(7{)}^{\prime }$, $\mathrm{S}\mathrm{U}(3{)}^{\prime }$ and/or their descendants are presented. A unified model based on $\mathrm{S}\mathrm{O}(10)\times \mathrm{S}\mathrm{O}(10{)}^{\prime }$ which embeds many of these models is constructed wherein three light sterile neutrinos are just as natural as the three ordinary neutrinos. These gauge models have relevance to current neutrino oscillation data, including the LSND anomaly.

We study the structure of fermionic mass eigenstates in a pure four-dimensional deconstruction approach. Unlike the case with the usual higher dimensional deconstruction (or latticized extra dimension), here the doubling of fermionic degrees of freedom is physical, thus there is no need to invoke Wilson terms to eliminate them. The fermionic structure is shaped by two key factors, namely, the boundary conditions on fermions and the ratio of two breaking scales involved. The singular value decomposition of linear algebra is employed to shed light into the phenomenologically crucial role of chiral boundary conditions. In this approach, we can explain the localization or “delocalization” nature of fermionic zero-mode in flavor space and obtain analytically all higher modes. The application of boundary conditions on fermions to the implementation of CKM quark mixing is also found.

The Einstein-Gauss-Bonnet equations projected from the bulk to brane lead to a complicated Friedmann equation which simplifies to $H^2\sim {\rho }^q$ in the asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to $q=2$ whereas $q=2/3$ and$q=1$ give rise to high-energy Gauss-Bonnet (GB) regime and the standard general relativity (GR), respectively. Amazingly, while evolving from RS regime to high-energy GB limit, one passes through a GR-like region which has important implications for brane world inflation. For tachyon GB inflation with potentials $V(\varphi )\sim {\varphi }^p$ investigated in this paper, the scalar to tensor ratio of perturbations $R$ is maximum around the RS region and is generally suppressed in the high-energy regime for the positive values of $p$. The ratio is very low for $p>0$ at all energy scales relative to GB inflation with ordinary scalar field. The models based upon tachyon inflation with polynomial type of potentials with generic positive values of $p$ turn out to be in the $1\sigma$ observational contour bound at all energy scales varying from GR to high-energy GB limit. The spectral index $n_S$ improves for the lower values of $p$ and approaches its scale invariant limit for $p=-2$ in the high-energy GB regime. The ratio $R$ also remains small for large negative values of $p$, however, difference arises for models close to scale invariance limit. In this case, the tensor to scale ratio is large in the GB regime whereas it is suppressed in the intermediate region between RS and GB. Within the framework of patch cosmologies governed by $H^2\sim {\rho }^q$, the behavior of ordinary scalar field near cosmological singularity and the nature of scaling solutions are distinguished for the values of $q<1$ and $q>1$. The tachyon dynamics, on the other hand, exhibits stable scaling solutions $\forall q$ if the adiabatic index of barotropic fluid $\gamma <1$.

A model-independent determination of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix (CKM) element $V_{us}$ from five measured strangeness-changing hyperon semileptonic decays is performed. Flavor $\mathrm{S}\mathrm{U}(3)$ symmetry breaking effects in the leading vector and axial-vector form factors are analyzed in the framework of the $1/N_c$ expansion of QCD. A fit to experimental data allows one to extract the value $V_{us}=0.2199\pm 0.0026$, which is comparable to the one from $K_{e3}$ decays. This reconciliation is achieved through second-order symmetry breaking effects of a few percent in the form factors $f_1$, which increase their magnitudes over their $\mathrm{S}\mathrm{U}(3)$ predictions.