## Tags » Mathematical Physics

#### Self-gravitating systems in Extended Gravity [CL]

http://arxiv.org/abs/1411.3143

Starting from the weak field limit, we discuss astrophysical applications of Extended Theories of Gravity where higher order curvature invariants and scalar fields are considered by generalizing the Hilbert-Einstein action linear in the Ricci curvature scalar $R$. 90 more words

Solar And Stellar Astrophysics

#### On the Geometric Structure of Flows I: The Referential Gradient. A Generally Covariant Measure of Flow Geometry [CL]

http://arxiv.org/abs/1411.2283

Assuming a-priori a smooth generating vector field, we introduce a generally covariant measure of the flow geometry called the referential gradient of the flow. The main result is the explicit relation between the referential gradient and the generating vector field, and is provided for from two equivalent perspectives: a Lagrangian specification with respect to a generalized parameter, and an Eulerian specification making explicit the evolution dynamics. 32 more words

Solar And Stellar Astrophysics

#### Dark Energy and Dark Matter in Stars Physic [CL]

http://arxiv.org/abs/1411.0242

We present the basic equations and relations for the relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which is {\em locally} equivalent to the f(R) theories of gravity and gives an alternative description of the effects of dark matter and dark energy. 83 more words

Cosmology And Nongalactic Astrophysics

#### Quantization as Deformation

Very early in my study of physics, Weyl became one of my gods. I use the word “god” rather than, say, “outstanding teacher” for the ways of gods are mysterious, inscrutable, and beyond the comprehension of ordinary mortals. 213 more words

#### Dynamical symmetries and observational constraints in scalar field cosmology [CL]

http://arxiv.org/abs/1410.4930

We propose to use dynamical symmetries of the field equations, in order to classify the dark energy models in the context of scalar field (quintessence or phantom) FLRW cosmologies. 169 more words

Cosmology And Nongalactic Astrophysics

#### Lattice Universe: examples and problems [CL]

http://arxiv.org/abs/1410.3909

We consider lattice Universes with spatial topologies $T\times T\times T$, $\; T\times T\times R\;$ and $\; T\times R\times R$. In the Newtonian limit of General Relativity, we solve the Poisson equation for the gravitational potential in the enumerated models. 142 more words

Cosmology And Nongalactic Astrophysics

#### Why are sound waves longitudinal?

“Give me some example for waves in nature! “

“Sound is a wave.. Light is a wave.. Of course we see water waves.. “