Cloud of strings in f(R) gravity

We derive the solution for a spherically symmetric string cloud configuration in a d-dimensional spacetime in the framework of f(R) theories of gravity. We also analyze some thermodynamic properties of the joint black hole - cloud of strings solution. For its Hawking temperature, we found that the dependence of the mass with the horizon is significantly different in both theories. For the interaction of a black hole with thermal radiation, we found that the shapes of the curves are similar, but shifted. Our analysis generalizes some known results in the literature.Comment: Version accepted for CP

Tsallis holographic dark energy in the Brans-Dicke cosmology

Using the Tsallis generalized entropy, holographic hypothesis and also considering the Hubble horizon as the IR cutoff, we build a holographic model for dark energy and study its cosmological consequences in the Brans-Dicke framework. At first, we focus on a non-interacting universe, and thereinafter, we study the results of considering a sign-changeable interaction between the dark sectors of the cosmos. Our investigations show that, compared with the flat case, the power and freedom of the model in describing the cosmic evolution is significantly increased in the presence of the curvature. The stability analysis also indicates that, independent of the universe curvature, both the interacting and non-interacting cases are classically unstable. In fact, both the classical stability criterion and an acceptable behavior for the cosmos quantities, including the deceleration and density parameters as well as the equation of state, are not simultaneously obtainable.Comment: Accepted version, Eur. Phys. J. C (2018

Energy definition and dark energy: a thermodynamic analysis

Accepting the Komar mass definition of a source with energy-momentum tensor $T_{\mu\nu}$, and using the thermodynamic pressure definition, we find a relaxed energy-momentum conservation law. Thereinafter, we study some cosmological consequences of the obtained energy-momentum conservation law. It has been found out that the dark sectors of cosmos are unifiable into one cosmic fluid in our setup. While this cosmic fluid impels the universe to enter an accelerated expansion phase, it may even show a baryonic behavior by itself during the cosmos evolution. Indeed, in this manner, while $T_{\mu\nu}$ behaves baryonically, some parts of it, namely $T_{\mu\nu}(e)$ which is satisfying the ordinary energy-momentum conservation law, are responsible for the current accelerated expansion.Comment: Accepted by AHE

The LISA PathFinder DMU and Radiation Monitor

The LISA PathFinder DMU (Data Management Unit) flight model was formally accepted by ESA and ASD on 11 February 2010, after all hardware and software tests had been successfully completed. The diagnostics items are scheduled to be delivered by the end of 2010. In this paper we review the requirements and performance of this instrumentation, specially focusing on the Radiation Monitor and the DMU, as well as the status of their programmed use during mission operations, on which work is ongoing at the time of writing.Comment: 11 pages, 7 figures, prepared for the Proceedings of the 8th International LISA Symposium, Classical and Quantum Gravit