Dark energy from scalar field with Gauss Bonnet and non-minimal kinetic coupling

We study a model of scalar field with a general non-minimal kinetic coupling to itself and to the curvature, and additional coupling to the Gauss Bonnet 4-dimensional invariant. The model presents rich cosmological dynamics and some of its solutions are analyzed. A variety of scalar fields and potentials giving rise to power-law expansion have been found. The dynamical equation of state is studied for two cases, with and without free kinetic term . In both cases phenomenologically acceptable solutions have been found. Some solutions describe essentially dark energy behavior, and and some solutions contain the decelerated and accelerated phases.Comment: 21 page

General Non-minimal Kinetic coupling to gravity

We study a new model of scalar field with a general non-minimal kinetic coupling to itself and to the curvature, as a source of dark energy, and analyze the cosmological dynamics of this model and the issue of accelerated expansion. A wide variety of scalar fields and potentials giving rise to power-law expansion have been found. The dynamical equation of state is studied for the two cases, without and with free kinetic term . In the first case, a behavior very close to that of the cosmological constant was found. In the second case, a solution was found, which match the current phenomenology of the dark energy. The model shows a rich variety of dynamical scenarios.Comment: 25 pages, 3 figures; figure added, references adde

Asymptotically free scalar curvature-ghost coupling in Quantum Einstein Gravity

We consider the asymptotic-safety scenario for quantum gravity which constructs a non-perturbatively renormalisable quantum gravity theory with the help of the functional renormalisation group. We verify the existence of a non-Gaussian fixed point and include a running curvature-ghost coupling as a first step towards the flow of the ghost sector of the theory. We find that the scalar curvature-ghost coupling is asymptotically free and RG relevant in the ultraviolet. Most importantly, the property of asymptotic safety discovered so far within the Einstein-Hilbert truncation and beyond remains stable under the inclusion of the ghost flow.Comment: 8 pages, 3 figures, RevTe

Non-minimal kinetic coupling and Chaplygin gas cosmology

In the frame of the scalar field model with non minimal kinetic coupling to gravity, we study the cosmological solutions of the Chaplygin gas model of dark energy. By appropriately restricting the potential, we found the scalar field, the potential and coupling giving rise to the Chaplygin gas solution. Extensions to the generalized and modified Chaplygin gas have been made.Comment: 18 pages, 2 figures. To appear in EPJ

Validity of Generalized Second Law of Thermodynamics in the Logamediate and Intermediate scenarios of the Universe

In this work, we have investigated the validity of the generalized second law of thermodynamics in logamediate and intermediate scenarios of the universe bounded by the Hubble, apparent, particle and event horizons using and without using first law of thermodynamics. We have observed that the GSL is valid for Hubble, apparent, particle and event horizons of the universe in the logamediate scenario of the universe using first law and without using first law. Similarly the GSL is valid for all horizons in the intermediate scenario of the universe using first law. Also in the intermediate scenario of the universe, the GSL is valid for Hubble, apparent and particle horizons but it breaks down whenever we consider the universe enveloped by the event horizon

Differences in temperature sensitivity and drought recovery between natural stands and plantations of conifers are species-specific

Forests are being impacted by climate and land-use changes which have altered their productivity and growth. Understanding how tree growth responds to climate in natural and planted stands may provide valuable information to prepare management in sight of climate change. Plantations are expected to show higher sensitivity to climate and lower post-drought resilience than natural stands, due to their lower compositional and structural diversity. We reconstructed and compared the radial growth of six conifers with contrasting ecological and climatic niches (Abies pinsapo, Cedrus atlantica, Pinus sylvestris, Pinus nigra, Pinus pinea, Pinus pinaster) in natural and planted stands subjected to seasonal drought in 40 sites. We quantified the relationships between individual growth variability and climate variables (temperature, precipitation and the SPEI drought index), as well as post-drought resilience. Elevated precipitation during the previous autumn-winter and current spring to early summer enhanced growth in both natural and planted stands of all species. Temperature effects on growth were less consistent: only plantations of A. pinsapo, C. atlantica, P. nigra, P. pinea, P. sylvetris and a natural stand of P. nigra showed negative impacts of summer temperature on growth. Drought reduced growth of all species in both plantations and natural stands, with variations in the temporal scale of the response. Drought constrained growth more severely in natural stands than in plantations of C. atlantica, P. pinaster and P. nigra, whereas the inverse pattern was found for A. pinsapo. Resilience to drought varied between species: natural stands of A. pinsapo, C. atlantica and P. pinaster recovered faster than plantations, while P. pinea plantations recovered faster than natural stands. Overall, plantations did not consistently show a higher sensitivity to climate and a lower capacity to recover after drought. Therefore, plantations are potential tools for mitigating climate warming. © 2021 The AuthorsThis study was supported by project FORMAL ( RTI2018-096884-B-C31 ) from the Spanish Ministry of Science, Innovation and Universities . GS-B was supported by a Spanish Ministry of Economy, Industry and Competitiveness Postdoctoral grant ( IJC2019-040571-I ; FEDER funds)

Effective Average Action in N=1 Super-Yang-Mills Theory

For N=1 Super-Yang-Mills theory we generalize the effective average action Gamma_k in a manifest supersymmetric way using the superspace formalism. The exact evolution equation for Gamma_k is derived and, introducing as an application a simple truncation, the standard one-loop beta-function of N=1 SYM theory is obtained.Comment: 17 pages, LaTeX, some remarks added, misprints corrected, to appear in Phys. Rev.

The Running of the Cosmological and the Newton Constant controlled by the Cosmological Event Horizon

We study the renormalisation group running of the cosmological and the Newton constant, where the renormalisation scale is given by the inverse of the radius of the cosmological event horizon. In this framework, we discuss the future evolution of the universe, where we find stable de Sitter solutions, but also "big crunch"-like and "big rip"-like events, depending on the choice of the parameters in the model.Comment: 14 pages, 7 figures, minor improvements, references adde

Holographic superconductor models in the non-minimal derivative coupling theory

We study a general class of holographic superconductor models via the St\"{u}ckelberg mechanism in the non-minimal derivative coupling theory in which the charged scalar field is kinetically coupling to Einstein's tensor. We explore the effects of the coupling parameter on the critical temperature, the order of phase transitions and the critical exponents near the second-order phase transition point. Moreover, we compute the electric conductive using the probe approximation and check the ratios $\omega_g/T_c$ for the different coupling parameters.Comment: 12 pages, 5 figure