An Einstein-like theory of gravity with a non-newtonian weak-field limit

We propose a model describing Einstein gravity coupled to a scalar field with an exponential potential. We show that the weak-field limit of the model has static solutions given by a gravitational potential behaving for large distances as \ln r . The Newtonian term GM/r appears only as subleading. Our model can be used to give a phenomenological explanation of the rotation curves of the galaxies without postulating the presence of dark matter. This can be achieved only by giving up at galactic scales Einstein equivalence principle.Comment: Final version, accepted for publication on General Relativity and Gravitatio

Induced gravity and entanglement entropy of 2D black holes

Using the fact that 2D Newton constant is wholly induced by a conformal field theory, we derive a formula for the entanglement entropy of the anti-de Sitter black hole in two spacetime dimensions. The leading term in the large black hole mass expansion of our formula reproduces exactly the Bekenstein-Hawking entropy S_{BH}, whereas the subleading term behaves as ln S_{BH}. This subleading term has the universal form typical for the entanglement entropy of physical systems described by effective conformal fields theories (e.g. one-dimensional statistical models at the critical point).Comment: 6 page

Holography of charged dilatonic black branes at finite temperature

We investigate bulk and holographic features of finite-temperature black brane solutions of 4D anti-de Sitter Einstein-Maxwell-dilaton-gravity (EMDG). We construct, numerically, black branes endowed with non trivial scalar hairs for broad classes of EMDG. We consider both exponential and power-law forms for the coupling functions, as well as several charge configurations: purely electric, purely magnetic and dyonic solutions. At finite temperature the field theory holographically dual to these black brane solutions has a rich and interesting phenomenology reminiscent of electron motion in metals: phase transitions triggered by nonvanishing VEV of scalar operators, non-monotonic behavior of the electric conductivities as function of the frequency and of the temperature, Hall effect and sharp synchrotron resonances of the conductivity in presence of a magnetic field. Conversely, in the zero temperature limit the conductivities for these models show a universal behavior. The optical conductivity has a power-law behavior as a function of the frequency, whereas the DC conductivity is suppressed at small temperatures.Comment: 29 pages 14 figures, typos corrected, reference adde

Hyperscaling violation for scalar black branes in arbitrary dimensions

We extend to black branes (BB) in arbitrary dimensions the results of Ref. [1] about hyperscaling violation and phase transition for scalar black 2-branes. We derive the analytic form of the (d+1)-dimensional scalar soliton interpolating between a conformal invariant AdS vacuum in the infrared and a scale covariant metric in the ultraviolet. We show that the thermodynamical system undergoes a phase transition between Schwarzschild-AdS and a scalar-dressed BB. We calculate the critical exponent and the hyperscaling violation parameter in the two phases. We show that our scalar BB solutions generically emerge as compactifications of p-brane solutions of supergravity theories. We also derive the short distance form of the correlators for the scalar operators corresponding to an UV exponential potential supporting our black brane solution. We show that also for negative values of the hyperscaling violation parameter these correlators have a short distance power-law behavior.Comment: Final version accepted for publication in JHE