A simple model of quintessential inflation with the modified exponential potential $e^{-\alpha \varphi }[A+(\varphi -{\varphi }_0{)}^2]$ is analyzed in the braneworld context. Considering reheating via instant preheating, it is shown that the evolution of the scalar field $\varphi$ from inflation to the present epoch is consistent with the observational constraints in a wide region of the parameter space. The model exhibits transient acceleration at late times for $0.96\lesssim A{\alpha }^2\lesssim 1.26$ and $271\lesssim {\varphi }_0\alpha \lesssim 273$, while permanent acceleration is obtained for $2.3\times {10}^{-8}\lesssim A{\alpha }^2\lesssim 0.98$ and $255\lesssim {\varphi }_0\alpha \lesssim 273$. The steep parameter $\alpha$ is constrained to be in the range $5.3\lesssim \alpha \lesssim 10.8$.

We constrain the thermal evolution of the universe with a decaying cosmological term by using the method of the analysis for the Wilkinson Microwave Anisotropy Probe (WMAP) observation data. The cosmological term is assumed to be a function of the scale factor that increases toward the early universe, and the radiation energy density is lower compared to that in the model with the standard cosmological constant ($\Lambda \mathrm{CDM}$). The decrease in the radiation density affects the thermal history of the universe; e.g. the photon decoupling occurs at higher-$z$ compared to the case of the standard $\Lambda \mathrm{CDM}$ model. As a consequence, a decaying cosmological term affects the cosmic microwave background (CMB) anisotropy. Thanks to the Markov-Chain Monte Carlo method, we compare the angular power spectrum in the decaying $\Lambda \mathrm{CDM}$ model with the CMB data, and we get severe constraints on parameters of the model.

Two independent measurements of the Newtonian gravitational constant $G$, with stated relative uncertainties below 20 ppm, have been reported in the literature. These measurements were carried out at significantly different separations between source and test masses. The close agreement between the two reported values is used to derive constraints on the existence of a single, composition-independent Yukawa interaction at intermediate ranges. These inferred limits are tighter than those obtained through direct search, for ranges between about 2 cm and 1 m. At a range of 10 cm, the improvement is by a factor of approximately 50.

We study the scalar Higgs sector of the next-to-minimal supersymmetric standard model with an extra $U(1)$, which has two Higgs doublets and a Higgs singlet, in the light leptophobic $Z^{\prime }$ scenario where the extra neutral gauge boson $Z^{\prime }$ does not couple to charged leptons. In this model, we find that the sum of the squared coupling coefficients of the three neutral scalar Higgs bosons to $ZZ$, normalized by the corresponding standard model coupling coefficient, is noticeably smaller than unity, due to the effect of the extra $U(1)$, for a reasonable parameter space of the model, whereas it is unity in the next-to-minimal supersymmetric standard model. Thus, these two models may be distinguished if the coupling coefficients of neutral scalar Higgs bosons to $ZZ$ are measured at the future International Linear Collider by producing them via the Higgs-strahlung, $ZZ$ fusion, and $WW$ fusion processes.

The role of neutrality constraints for the phase structure of QCD at nonvanishing chemical potentials is studied within a self-consistent truncation scheme for the Dyson-Schwinger equation of the quark propagator in Landau gauge. We find the (approximate) color-flavor-locked phase to be energetically preferred at all potentially relevant densities and for physical values of the quark masses. We furthermore observe the impossibility to define this phase by residual global symmetries and discuss the role of chemical potentials.

The perturbative QCD formula for minijet production constitutes an important ingredient in models describing the total cross section and multiparticle production in hadron-hadron scattering at high energies. Using arguments based on $s$-channel unitarity we set bounds on the minimum value of $pt$ for which the leading-twist minijet formula can be used. For large impact parameters where correlations between partons appear to be small we find that the minimum value of $p_t^c$ should be greater than 2.5 GeV for LHC energies and greater than 3.5 GeV for cosmic ray energies of about 50 TeV. We also argue that for collisions with values of impact parameters typical for heavy particle production the values of minimum $p_t$ are likely to be considerably larger. We also analyze and quantify the potential role of saturation effects in the gluon density. We find that although saturation effects alone are not sufficient to restore unitarity, they are likely to play an important role at LHC energies.

The ${\tau }^{-}\to \eta {\pi }^{-}{\pi }^{+}{\pi }^{-}{\nu }_{\tau }$ decay with the $\eta \to \gamma \gamma$ mode is studied using $384{\mathrm{fb}}^{-1}$ of data collected by the BABAR detector. The branching fraction is measured to be $(1.60\pm 0.05\pm 0.11)\times {10}^{-4}$. It is found that ${\tau }^{-}\to f_1(1285){\pi }^{-}{\nu }_{\tau }\to \eta {\pi }^{-}{\pi }^{+}{\pi }^{-}{\nu }_{\tau }$ is the dominant decay mode with a branching fraction of $(1.11\pm 0.06\pm 0.05)\times {10}^{-4}$. The first error on the branching fractions is statistical and the second systematic. Note that no particle identification algorithm is applied to the charged tracks to distinguish pions from kaons. In addition, a 90% confidence level upper limit on the branching fraction of the ${\tau }^{-}\to {\eta }^{\prime }(958){\pi }^{-}{\nu }_{\tau }$ decay is measured to be $7.2\times {10}^{-6}$. This last decay proceeds through a second-class current and is expected to be forbidden in the limit of isospin symmetry.

We discuss a dynamical matrix model by which probability distribution is associated with Gaussian ensembles from random matrix theory. We interpret the matrix $M$ as a Hamiltonian representing interaction of a bosonic system with a single fermion. We show that a system of second-quantized fermions influences the ground state of the whole system by producing a gap between the highest occupied eigenvalue and the lowest unoccupied eigenvalue.

The staid subject of exact static spherically symmetric perfect fluid solutions of Einstein’s equations has been reinvigorated in the last decade. We now have several solution generating techniques which give rise to new exact solutions. Here the Einstein static universe is transformed into a physically acceptable solution the properties of which are examined in detail. The emphasis here is on the importance of the integration constants that these generating techniques introduce.

We present a new static solution to the 5D Einstein-Maxwell equations describing a static black hole surrounded by a nonrotating dipole black ring. The configuration is kept in equilibrium by an external magnetic field interacting with the dipole charge of the black ring. The properties of the black Saturn-like configuration are studied and the basic physical quantities are calculated. The solution demonstrates 2-fold continuous nonuniqueness of the 5D magnetized static neutral black objects for fixed total mass and Melvin background.

In a previous article we have shown the existence of a new independent ${\mathcal{R}}^4$ term, at one loop, in the type IIA and heterotic effective actions, after reduction to four dimensions, besides the usual square of the Bel-Robinson tensor. It had been shown that such a term could not be directly supersymmetrized, but we showed that was possible after coupling to a scalar chiral multiplet. In this article, we study the extended $(\mathcal{N}=8)$ supersymmetrization of this term, where no other coupling can be taken. We show that such supersymmetrization cannot be achieved at the linearized level. This is in conflict with the theory one gets after toroidal compactification of type II superstrings being $\mathcal{N}=8$ supersymmetric. We interpret this result in the face of the recent claim that perturbative supergravity cannot be decoupled from string theory in $d\ge 4$, and $\mathcal{N}=8$, $d=4$ supergravity is in the swampland.

We present a solution of Einstein equations with quintessential matter surrounding a $d$-dimensional black hole, whose asymptotic structures are determined by the state of the quintessential matter. We examine the thermodynamics of this black hole and find that the mass of the black hole depends on the equation of state of the quintessence, while the first law is universal. Investigating the Hawking radiation in this black hole background, we observe that the Hawking radiation dominates on the brane in the low-energy regime. For different asymptotic structures caused by the equation of state of the quintessential matter surrounding the black hole, we learn that the influences by the state parameter of the quintessence on Hawking radiation are different.

We investigate the Wightman function, the vacuum expectation values of the field squared, and the energy-momentum tensor for a scalar field with a general curvature coupling parameter in $(D+1)$-dimensional de Sitter (dS) spacetime with an arbitrary number of compactified spatial dimensions. Both cases of periodicity and antiperiodicity conditions along the compactified dimensions are considered. Recurrence formulas are derived which express the vacuum expectation values for the dS spacetime of topology ${\mathrm{R}}^p\times ({\mathrm{S}}^1{)}^q$ in the form of the sum of the vacuum expectation values in the topology ${\mathrm{R}}^{p+1}\times ({\mathrm{S}}^1{)}^{q-1}$ and the part induced by the compactness of the $(p+1)$th spatial dimension. The behavior of the topological parts is investigated in various asymptotic regions of the parameters. In the early stages of the cosmological evolution, the topological parts dominate the contribution in the expectation values due to the uncompactified dS part. In this limit the behavior of the topological parts does not depend on the curvature coupling parameter and coincides with that for a conformally coupled massless field. At late stages of the cosmological expansion, the expectation values are dominated by the part corresponding to uncompactified dS spacetime. The vanishing of the topological parts is monotonic or oscillatory in dependence of the mass and the curvature coupling parameter of the field.

Finsler geometry has been recently rediscovered as an interesting possibility to describe spacetime geometry beyond Riemannian geometry. The most evident effect of this class of models is the prediction of modified dispersion relations for particles moving in such backgrounds. In this paper, we are going to consider the effects of modified dispersion relations on a gauge field theory with spontaneous symmetry breaking associated with a Higgs field. The percolation of higher dimensional, Lorentz violating operators to lower dimensional ones is discussed. We also discuss the issue of spontaneous symmetry breaking in a monometric Finsler scenario like the one associated with the so-called very special relativity.

In a large region of the supersymmetry parameter space, the annihilation cross section for neutralino dark matter is strongly dependent on the relative velocity of the incoming particles. We explore the consequences of this velocity dependence in the context of indirect detection of dark matter from the galactic center. We find that the increase in the annihilation cross section at high velocities leads to a flattening of the halo density profile near the galactic center and an enhancement of the annihilation signal. For the models considered, the annihilation signal can be doubled. These models are typically undetectable by current experiments in spite of the enhancement.

We search Hubble Space Telescope Treasury Program images collected as part of the Great Observatories Origins Deep Survey for pairs of galaxies consistent with the gravitational lensing signature of a cosmic string. Our technique includes estimates of the efficiency for finding the lensed galaxy pair. In the north (south) survey field we find no evidence out to a redshift of greater than 0.5 (0.3) for cosmic strings to a mass per unit length limit of $G\mu /c^2<3.0\times {10}^{-7}$ at 95% confidence limits (C.L.). In the combined $314.9{\mathrm{arcmin}}^2$ of the north and south survey fields this corresponds to a global limit on ${\Omega }_{\mathrm{strings}}<0.02$. Our limit on $G\mu /c^2$ is more than an order of magnitude lower than searches for individual strings in cosmic microwave background (CMB) data. Our limit is higher than other CMB and gravitational wave searches, however, we note that it is less model dependent than these other searches.

Models where the dark energy is a scalar field with a nonstandard Dirac-Born-Infeld (DBI) kinetic term are investigated. Scaling solutions are studied and proven to be attractors. The corresponding shape of the brane tension and of the potential is also determined and found to be, as in the standard case, either exponentials or power law of the DBI field. In these scenarios, in contrast to the standard situation, the vacuum expectation value of the field at small redshifts can be small in comparison to the Planck mass which could be an advantage from the model building point of view. This situation arises when the present-day value of the Lorentz factor is large, this property being per se interesting. Serious shortcomings are also present such as the fact that, for simple potentials, the equation of state appears to be too far from the observational favored value $-1$. Another problem is that, although simple stringy-inspired models precisely lead to the power-law shape that has been shown to possess a tracking behavior, the power index turns out to have the wrong sign. Possible solutions to these issues are discussed.

We study preheating in $\mathcal{N}$-flation, assuming the Marčenko-Pastur mass distribution, equal-energy initial conditions at the beginning of inflation and equal axion-matter couplings, where matter is taken to be a single, massless bosonic field. By numerical analysis we find that preheating via parametric resonance is suppressed, indicating that the old theory of perturbative preheating is applicable. While the tensor-to-scalar ratio, the non-Gaussianity parameters and the scalar spectral index computed for $\mathcal{N}$-flation are similar to those in single-field inflation (at least within an observationally viable parameter region), our results suggest that the physics of preheating can differ significantly from the single-field case.

In this paper we study the flat ($k=0$) cosmological Friedmann-Robertson-Walker model with holonomy corrections of loop quantum gravity. The considered universe contains a massless scalar field and the cosmological constant $\Lambda$. We find analytical solutions for this model in different configurations and investigate its dynamical behavior in the whole phase space. Such an approach might be significant e.g. as a phenomenological reference for a further, fully quantum treatment. We show the explicit influence of $\Lambda$ on the qualitative and quantitative character of solutions. Even in the case of positive $\Lambda$ the oscillating solutions without the initial and final singularity appear as a generic case for some quantization schemes.

We consider a minimal extension of the standard model where a real, gauge singlet scalar field is added to the standard spectrum. Introducing the Ansatz of universality of scalar couplings, we are led to a scenario which has a set of very distinctive and testable predictions: (i) the mixing between the standard model Higgs and the new state is near maximal, (ii) the ratio of the two Higgs mass eigenstates is fixed ($\sim \sqrt{3}$), (iii) the decay modes of each of the two eigenstates are standard model like. We also study how electroweak precision tests constrain this scenario. We predict the lighter Higgs to lie in the range of 114 and 145 GeV, and hence the heavier one between 198 and 250 GeV. The predictions of the model can be tested at the upcoming LHC.