In this paper the quantum vacuum energies induced by massive fluctuations of one real scalar field on a configuration of two partially transparent plates are analyzed. The physical properties of the infinitely thin plates are characterized by two Dirac-$\delta$ potentials. We find that an attractive or repulsive Casimir force arises between the plates when the weights of the $\delta$’s have equal or different sign. If some of the plates absorb fluctuations below some threshold of energy (the corresponding weight is negative), there is the need to set a minimum mass to the scalar field fluctuations to preserve unitarity in the corresponding quantum field theory. Two repulsive $\delta$ interactions are compatible with massless fluctuations. The effect of Dirichlet boundary conditions at the endpoints of the interval $(-a,a)$ on a massless scalar quantum field theory defined on this interval is tantamount to letting the weights of the repulsive $\delta$ interactions go to $+\infty$.

We consider a possibility that the cosmological constant may not be a constant, but a free thermodynamical variable. To this end we construct a microscopic model of a spacelike two-sphere just inside of the cosmological horizon of the de Sitter spacetime. In our model the spacelike two-sphere in question is assumed to consist of discrete constituents, each of them contributing to the two-sphere an area, which is an integer times a constant. Using our model we obtain a thermodynamical equation of state for the cosmological constant. Our equation of state implies that the cosmological constant has a certain positive lower bound, which depends on the number of the constituents of the two-sphere.

The big bang singularity could be understood as a breakdown of Einstein’s general relativity at very high energies. By adopting this viewpoint, other theories that implement Einstein cosmology at high energies might solve the problem of the primeval singularity. One of them is loop quantum cosmology (LQC) with a small cosmological constant that models a universe moving along an ellipse, which prevents singularities like the big bang or the big rip, in the phase space $(H,\rho )$, where $H$ is the Hubble parameter and $\rho$ the energy density of the universe. Using LQC one considers a model universe filled by radiation and matter where, due to the cosmological constant, there are a de Sitter and an anti–de Sitter solution. This means that one obtains a bouncing nonsingular universe which is in the contracting phase at early times. After leaving this phase, i.e., after bouncing, it passes trough a radiation- and matter-dominated phase and finally at late times it expands in an accelerated way (current cosmic acceleration). This model does not suffer from the horizon and flatness problems as in big bang cosmology, where a period of inflation that increases the size of our universe in more than 60 e-folds is needed in order to solve both problems. The model has two mechanisms to avoid these problems: the evolution of the universe through a contracting phase and a period of super inflation ($\dot{H}>0$).

The primordial black hole (PBH) formation is studied in light of the inflating curvaton. The typical scale of the PBH formation is determined by curvaton inflation, which may generate PBH with ${10}^{14}\mathrm{g}\le M_{\mathrm{PBH}}\le {10}^{38}\mathrm{g}$ when curvaton inflation gives the number of e-foldings $5\le N_2\le 38$. The non-Gaussianity of the inflating curvaton does not prevent the PBH formation.

We resum a class of large Sudakov logarithms affecting Higgs-boson production in the exclusive one-jet bin at the LHC. We extend previous results by calculating the full one-loop soft function for this process, which extends the accuracy of the resummation to include the leading three logarithmic corrections at each order in the QCD coupling constant. We match this result to the next-to-leading order cross section and present a detailed numerical study assuming realistic LHC cuts. Careful attention is paid to the matching procedure, and to the theoretical uncertainties induced by residual scale variation. We find that the matched ${\mathrm{NLL}}^{\prime }+\mathrm{NLO}$ cross section has significantly smaller uncertainties than the fixed-order result, and can be used to alleviate the theoretical errors hindering current Higgs analyses at the LHC.

We propose a model-independent analysis of the neutrino mass matrix through an expansion in terms of the eigenvectors defining the lepton mixing matrix, which we show can be parametrized as small perturbations of the tribimaximal mixing eigenvectors. This approach proves to be powerful and convenient for some aspects of lepton mixing, in particular when studying the sensitivity of the mass matrix elements to departures from their tribimaximal form. In terms of the eigenvector decomposition, the neutrino mass matrix can be understood as originating from a tribimaximal dominant structure with small departures determined by data. By implementing this approach to cases when the neutrino masses originate from different mechanisms, we show that the experimentally observed structure arises very naturally. We thus claim that the observed deviations from the tribimaximal mixing pattern might be interpreted as a possible hint of a “hybrid” nature of the neutrino mass matrix.

In a recent paper Emparan et al. [arXiv:1302.6382] studied general relativity in the limit in which the number of spacetime dimensions $D$ tends to infinity. They showed that, in such limit, the theory simplifies notably. It reduces to a theory whose fundamental objects, black holes and black branes, behave as noninteracting particles. Here, we consider a different way of extending gravity to $D$ dimensions. We present a special limit of dimensionally continued gravity in which black holes retain their gravitational interaction at large $D$ and still have entropy proportional to the mass. The similarities and differences with the limit considered in Emparan et al. [arXiv:1302.6382] are discussed.

We provide a formula for the scaling behavior of the inflationary bispectrum in the “squeezed” limit where one momentum becomes much smaller than the other two. This determines the scaling of the halo bias at low wave number and will be an important observable for the next generation of galaxy surveys. Our formula allows it to be predicted for the first time for a generic inflationary model with multiple light, canonically-normalized scalar fields.

The extremely small accelerations of objects required for the onset of modified Newtonian dynamics, or modified Newtonian dynamics (MOND), makes testing the hypothesis in conventional terrestrial laboratories virtually impossible. This is due to the large background acceleration of Earth, which is transmitted to the acceleration of test objects within an apparatus. We show, however, that it may be possible to test MOND-type hypotheses with experiments using a conventional apparatus capable of tracking very small accelerations of its components but performed in locally inertial frames such as artificial satellites and other freely falling laboratories. For example, experiments involving an optical interferometer or a torsion balance in these laboratories would show nonlinear dynamics and displacement amplitudes larger than expected. These experiments may also be able to test potential violations of the strong equivalence principle by MOND and to distinguish between its two possible interpretations (modified inertia and modified gravity).

We take a new look at the DeWitt equation, a defining equation for the effective action functional in quantum field theory. We present a formal solution to this equation and discuss the equation in various contexts, and in particular for models where it can be made completely well defined, such as the Wess-Zumino model in two dimensions.

The finite temperature chiral condensate for $2+1$ quark flavors is considered in the framework of the hadron resonance gas model. This requires some dynamical information, for which two models are employed: one based on the quark structure of hadrons combined with the Nambu–Jona-Lasinio approach to chiral symmetry breaking, and one originating from gauge/gravity duality. Using these insights, hadronic sigma terms are discussed in the context of recent first-principles results following from lattice QCD and chiral perturbation theory. For the condensate, in generic agreement with lattice data it is found that chiral symmetry restoration in the strange quark sector takes place at higher temperatures than in the light quark sector. The importance of this result for a recently proposed dynamical model of hadronic freeze-out in heavy ion collisions is outlined.

It has been shown that well-behaved spacetimes may induce the vacuum fluctuations of some nonminimally coupled free scalar fields to go through a phase of exponential growth. Here, we discuss this mechanism in the context of spheroidal thin shells emphasizing the consequences of deviations from spherical symmetry.

We develop a systematic classical framework to accommodate the canonical quantization of geometric and matter perturbations on a quantum homogeneous isotropic flat spacetime. The existing approach of standard cosmological perturbations is indeed proved to be good only up to first order in the inhomogeneities, and only if the background is treated classically. To consistently quantize the perturbations and the background, a new set of classical phase-space variables is required. We show that, in a natural gauge, a set of such Dirac observables exists, and their algebra is of the canonical form. Finally, we compute the physical Hamiltonian that generates the dynamics of such observables with respect to the homogeneous part of a Klein-Gordon “clock” field $T$. The results of this work provide a good starting point to understanding and calculating the effects that quantum cosmological spacetime in the background has on the quantum perturbations of the metric tensor and of matter fields.

We consider configurations consisting of a neutron star with a wormhole at the core. The wormhole is held open by a ghost scalar field with a quartic coupling. The neutron matter is described by a perfect fluid with a polytropic equation of state. We obtain static regular solutions for these systems. A stability analysis, however, shows that they are unstable with respect to linear perturbations.

We present an inflationary model preceded by a bounce in a metric theory à la $f(R)$, where $R$ is the scalar curvature of the space-time. The model is asymptotically de Sitter such that the gravitational action tends asymptotically to an Einstein-Hilbert action with an effective cosmological constant; therefore, modified gravity affects only the early stages of the Universe. We then analyze the spectrum of the gravitational waves through the method of the Bogoliubov coefficients by two means: taking into account the gravitational perturbations due to the modified gravitational action in the $f(R)$ setup and simply considering those perturbations inherent to the standard Einstein-Hilbert action. We show that there are distinctive (oscillatory) signals on the spectrum for very low frequencies; i.e., corresponding to modes that are currently entering the horizon.

In the context of $f(R,T)$ theories of gravity, we study the evolution of scalar cosmological perturbations in the metric formalism. According to restrictions on the background evolution, a specific model within these theories is assumed in order to guarantee the standard continuity equation. Using a completely general procedure, we find the complete set of differential equations for the matter density perturbations. In the case of sub-Hubble modes, the density contrast evolution reduces to a second-order equation. We show that for well-motivated $f(R,T)$ Lagrangians the quasistatic approximation yields to very different results from the ones derived in the frame of the concordance $\Lambda \mathrm{CDM}$ model constraining severely the viability of such theories.

Compared with that of standard dark matter halos, the density profile of the recently proposed new kind of dark matter structure named ultracompact minihalos (UCMHs) is steeper and its formation time is earlier. If the dark matter is composed of weakly interactive massive particles, the potential signals, e.g., neutrinos, from UCMHs due to dark matter annihilation would be detected by IceCube/DeepCore or other detectors and such signals would have a very useful complementarity of $\gamma$-ray observations. On the other hand, the formation of UCMHs is related to primordial curvature perturbations on the smaller scales. So constraints on the abundance of UCMHs can be used to give a limit on the perturbations on these scales. In previous works in the literature, the authors focused on the $\gamma$-ray signals from UCMHs due to dark matter annihilation. In this work, we investigate the neutrino signals from nearby UCMHs. Although no excess of neutrino signals from dark matter annihilation has been observed, the constraints on the abundance of UCMHs can be obtained and these constraints can be translated into the limit on the primordial curvature perturbations on small scales.

Reheating after $R^2$ inflation proceeds through gravitational particle production of conformally noninvariant fields. We argue that the nonvanishing expectation value of flat directions generic in supersymmetric theories break conformal invariance of the fields coupled to them in a position-dependent manner due to quantum fluctuations. As a result modulated reheating can occur after the supergravity $R^2$-inflation. The resultant curvature fluctuation is a mixture of the one produced during inflation and that produced by modulated reheating. The spectral index takes a value between $n_s=0.960$ and 0.983, the nonlinearity parameter of the local-type non-Gaussianity can be $f_{\mathrm{NL}}\sim \pm 10$, and the tensor-to-scalar ratio is $r\le 4\times {10}^{-3}$.

Non-Gaussianities in the cosmic microwave background maps arising from correlations between lensing and time variations of the gravitational potential (the so-called integrated Sachs-Wolfe effect) are one of the most important contaminants to the determination of the primordial inflationary bispectrum and may bias its determination. The presence of an extra dark radiation component, as suggested by some recent osmic microwave background measurements from the South Pole Telescope, could bias the expected value of the local bispectrum. In this paper we investigate the impact of dark radiation on the local bispectrum. As a by-product we also quantify the additional information on the dark radiation component that could come from a future precise measurement of the lensing-integrated-Sachs-Wolfe bispectrum.

Observations of low-metallicity halo stars have revealed a puzzling result: the abundance of ${}^7\mathrm{Li}$ in these stars is at least three times lower than their predicted primordial abundance. It is unclear whether the cause of this disagreement is a lack of understanding of lithium destruction mechanisms in stars or the non-standard physics behind the big bang nucleosynthesis (BBN). Uncertainties related to the destruction of lithium in stars can be circumvented if lithium abundance is measured in the “pristine” gas of the low metallicity systems. The first measurement in one such system, the small magellanic cloud (SMC), was found to be at the level of the pure expected primordial value, but is on the other hand, just barely consistent with the expected galactic abundance for the system at the SMC metallicity, where important lithium quantity was also produced in interactions of galactic cosmic rays and presents an addition to the already present primordial abundance. Because of the importance of the SMC lithium measurement for the resolution of the lithium problem, we here draw attention to the possibility of another post-BBN production channel of lithium, which could present an important addition to the observed SMC lithium abundance. Besides standard galactic cosmic rays, additional post-BBN production of lithium might come from cosmic rays accelerated in galaxy-galaxy interactions. This might be important for a system such is the SMC, which has experienced galaxy harassment in its history. Within a simplified but illustrative framework we demonstrate that large-scale tidal shocks from a few galactic fly-bys can possibly produce lithium in amounts comparable to those expected from the interactions of galactic cosmic-rays produced in supernovae over the entire history of a system. In case of the SMC, we find that only two such fly-bys could possibly account for as much lithium as the standard, galactic cosmic ray production channel. However, adding any a new mechanism for post-BBN production of lithium, like the one proposed here, would contribute to the observed SMC lithium abundance, causing this measurement to be more in tension with the primordial abundance predicted by the standard BBN.