Homogeneity

 

What are the observational limits on the homogeneity of matter at large distances given that we can only observe matter on our backward light cone?  The isotropy of the cosmic background radiation puts some constraints on the matter homogeneity at the time of decoupling. What does this tell us?

The isotropy of the cosmic background radiation puts some constraints on the matter homogeneity at the time of decoupling. What does this tell us?

3 de agosto de 2012

1208.0462 Conditional Symmetries and the Canonical Quantization of Constrained Minisuperspace Actions: the Schwarzschild case

T. Christodoulakis∗, N. Dimakis†, Petros A. Terzis‡
Nuclear and Particle Physics Section, Physics Department,
University of Athens, GR 157–71 Athens
G. Doulis§
Department of Mathematics and Statistics, University of Otago
P.O. Box 56, Dunedin 9010, New Zealand
Th. Grammenos¶
Department of Civil Engineering, University of Thessaly,
GR 383–34 Volos
E. Melask
Logistics Department, GR 32-200, Thiva
Technological Educational Institution of Chalkida
A. Spanou∗∗
School of Applied Mathematics and Physical Sciences,
National Technical University of Athens, GR 157–80, Athens

Abstract: A conditional symmetry is defined, in the phase-space of a quadratic in velocities constrained action, as a simultaneous conformal symmetry of the supermetric and the superpotential. It is proven that such a symmetry corresponds to a variational (Noether) symmetry.The use of these symmetries as quantum conditions on the wave-function entails a kind of selection rule. As an example, the minisuperspace model ensuing from a reduction of the Einstein - Hilbert action by considering static, spherically symmetric configurations and r as the independent dynamical variable, is canonically quantized. The conditional symmetries of this reduced action are used as supplementary conditions on the wave function. Their integrability conditions dictate, at a first stage, that only one of the three existing symmetries can be consistently imposed. At a second stage one is led to the unique Casimir invariant, which is the product of the remaining two, as the only possible second condition on. The uniqueness of the dynamical evolution implies the need to identify this quadratic integral of motion to the reparametrisation generator. This can be achieved by fixing a suitable parametrization of the r-lapse function, exploiting the freedom to arbitrarily rescale it. In this particular parametrization the measure is chosen to be the determinant of the supermetric. The solutions to the combined Wheeler - DeWitt and linear conditional symmetry equations are found and seen to depend on the product of the two “scale factors”.

2 de agosto de 2012

1208.0021 Observational Constraints on Nfields Phantom Power-Law

IftikharAhmad , Farah Naz. Institute of Physics and Mathematical Sciences,
Department of Mathematics, University of Gujrat. Gujrat, Pakistan.

Abstract: In the multi-fields Phantom power law we investigate the analytical behavior of many scalar fields working collectively, where 'i is the ith scalar field. Furthermore, we evaluate its parameter values by applying certain constraints on our model parameters, and then compare these values with current observational data from Observational data of CMB, BAO and H0. Through our results, we deeply observe that in the dark-energy EOS parameter at the Big Rip always finite with the pressure and dark energy density divergence.
Keywords: phantom power-law Cosmology, multi-fields.

1208.0025 Stability of a non-minimally conformally coupled scalar field in F(T )cosmology

Mubasher Jamil,1, 2, ∗ D. Momeni,2, † and Ratbay Myrzakulov2, ‡
1Center for Advanced Mathematics and Physics (CAMP), National University of Sciences and Technology (NUST), H-12, Islamabad, Pakistan
2Eurasian International Center for Theoretical Physics,
L.N. Gumilyov Eurasian National University, Astana 010008, Kazakhstan

Abstract: In this paper, we introduce a non-minimally conformally coupled scalar field and dark matter in F(T ) cosmology and study their dynamics. We investigate the stability and phase space behavior of the parameters of the scalar field by choosing an exponential potential and cosmologically viable form of F(T ). We found that the dynamical system of equations admit two unstable critical points, thus no attractor solutions exist in this cosmology. Furthermore taking into account the scalar field mimicking as quintessence and phantom energy, we discuss the corresponding cosmic evolution for both small and large times. We investigate the cosmological implications of the model via equation of state and deceleration parameters of our model and show that the late time Universe will be dominated by phantom energy and moreover phantom crossing is possible. Our results have no explicit predictions for inflation and early Universe era.

Keywords: Cosmology; torsion; stability; scalar fields; quintessence; phantom energy.
PACS numbers: 04.20.Fy; 04.50.+h; 98.80.-k

Eur. Phys. J. C (2012) 72:2075

1208.00615 Quintom phase-space: beyond the exponential potential
Genly Leon. Departamento de Matemática, Universidad Central de Las Villas, C. P. 53840, Santa Clara, Cuba and Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4950, Valparaíso, Chile.
Yoelsy Leyva† and J. Socorro‡. Departamento de Física, DCI, Universidad de Guanajuato-Campus León, C.P. 37150, Le´on, Guanajuato, México.

Abstract: We investigate the phase-space structure of the quintom dark energy paradigm in the framework of spatially flat and homogeneous universe. Considering arbitrary decoupled potentials, we find certain general conditions under which the the phantom dominated solution is late time attractor, generalizing previous results found for the case of exponential potential. Center Manifold Theory is employed to obtain sufficient conditions for the instability of de Sitter solution either with phantom or quintessence potential dominance. Another important issue is concerning the existence of a point corresponding to the standard quintessence dominated solution, which under certain condition on the potential, can mimic the dark matter behavior. This feature has important cosmological consequences to address de unified description of dark matter and dark energy in a single field.

1208.00103 Galileon Black Holes
Massimiliano Rinaldi. Namur Center for Complex systems (naXys), University of Namur, Belgium

Abstract: We study the spherically symmetric solutions to the gravitational field equations with a derivative coupling to a massless scalar field. This configuration is motivated by Galileon gravity as it preserves shift invariance in the scalar sector. We obtain exact black hole solutions that are similar to asymptotically de Sitter or anti-de Sitter black holes, according to the sign of the coupling constant
of the Galileon term. We examine the spacetime structure and the thermodynamical properties of these solutions, and we reveal the non-perturbative nature of the coupling constant. We find a phase transition, similar to the one described by Hawking and Page, which occurs at a critical temperature determined by both the black hole mass and by the strength of the coupling.

1 de agosto 2012

1 de agosto 2012

1208.0001 Galactic Phase Spaces
D. CHAKRABARTY
Department of Statistics, University of Warwick, Coventry CV4 7AL, U.K.

Galaxies are argued to manifest complexity, thereby contradicting models of smooth parametric galactic phase space densities. An estimation of chaos in models of our galaxy is forwarded to suggest strength and possible causes of non-linearities in phase space. A Bayesian nonparametric methodology that is designed to acknowledge uncertainties in measured data, when applied to an observed external galaxy, indicates a non-linear galactic phase space density that could result from a bistable system potential. The effect of such a phase space structure on the inverse modelling of phase space data is discussed.
Keywords: Non-linear dynamics; Hypothesis testing; Bayesian non-parametrics

Read More: http://www.worldscientific.com/doi/abs/10.1142/9789814383295_0021

Proceedings of the 7th International Workshop on Data Analysis in Astronomy “Livio Scarsi and Vito DiGesù”
Erice, Sicily, Italy, 15 – 21 April 2011

1208.0002 Dark Matter via Many Copies of the Standard Model
Alexander Vikman
Center for Cosmology and Particle Physics, NYU, New York, NY 10003, USA

In this proceedings I review our results from [1] where we have demonstrated that baryons in many possible hidden copies of the standard model can naturally account for the dark matter. The right abundance of the hidden-sector baryons and the correct spectrum of density perturbations are simultaneously generated during modulated reheating. We have also shown that for natural values of inflaton coupling constants, dictated by unitarity, the dark-matter abundance is predicted to be proportional to the ratio of observed cosmological parameters: the square of the amplitude of cosmological perturbations and the baryon-to-photon number ratio.

Read More: http://www.worldscientific.com/doi/abs/10.1142/9789814374125_0019

Proceedings of the International School of Subnuclear Physics
Erice, Sicily, Italy, 29 August – 7 September 2009

1208.0003 21 cm cosmology in the 21st century
Jonathan R Pritchard and Abraham Loeb
Institute for Theory and Computation, Harvard University, 60 Garden St., Cambridge, MA 02138, USA
E-mail: jpritchard@cfa.harvard.edu and aloeb@cfa.harvard.edu

Imaging the Universe during the first hundreds of millions of years remains one of the exciting challenges facing modern cosmology. Observations of the redshifted 21 cm line of atomic hydrogen offer the potential of opening a new window into this epoch. This will transform our understanding of the formation of the first stars and galaxies and of the thermal history of the Universe. A new generation of radio telescopes is being constructed for this purpose with the first results starting to trickle in. In this review, we detail the physics that governs the 21 cm signal and describe what might be learnt from upcoming observations. We also generalize our
discussion to intensity mapping of other atomic and molecular lines.

Rep. Prog. Phys. 75 (2012) 086901 (35pp)

1208.0004 El 1 de agosto del 2012, Martín Huarte Espinosa, defendio su tesis doctoral en la Universidad de Cambridge (http://www.mrao.cam.ac.uk/~mh475/) Título: Modelling feedback and magnetic fields in radio galaxy evolution. Keywords: MHD, turbulence, methods: numerical, galaxies: active, intergalactic medium, galaxies: jets Abstract: The intra-cluster medium (ICM) in galaxy clusters contains magnetic fields on Mpc scales. The main probe of these cluster magnetic fields (CMFs) is the Faraday rotation of the polarized emission from radio sources that are either embedded in, or behind the ICM. Several questions are open concerning the structure and evolution of the magnetic fields in both the ICM and the radio sources. We present three-dimensional magnetohydrodynamical numerical simulations to study randomly tangled magnetic fields in the core of a cluster under the effects of light and hypersonic AGN jets. We investigate the power of the jets and carry out synthetic observations to explore the observational signatures of our model radio sources. Our polarization maps agree with the observations, and show that the magnetic structure inside the sources is shaped by the backflow of the jets. Filaments in the synthetic synchrotron emissivity maps suggest that turbulence develops in evolved sources. The polarimetry statistics correlate with time, with the viewing angle and with the jet-to-ambient density contrast. As the sources expand, the linear polarization fraction decreases and the magnetic structure inside thin sources seems more uniform than inside fat ones. Moreover, we see that the jets distort and amplify the CMFs especially at the head of the jets and that this effect correlates with the power and evolution of the jets. We find good agreement with the RM fluctuations of Hydra A. One of the most important results is that the jet-produced RM enhancements may lead to an overestimate of the strength of the CMFs by a factor of about 70%. The physics of radio source expansion may explain the flattening of the RM structure functions at large scales. The advection of metals from a central active galaxy to the ICM in a cool-core cluster is also investigated with an additional suite of hydrodynamical simulations. These metals provide information about the ICM dynamical history and of the CMFs as well. The metal distribution model of the galaxy includes metal injection via star formation. After a cooling flow is established in our simulations, highly-hypersonic and light jets are injected with a range of intermittent active phases. The resulting AGN relic bubbles advect gas and metals from the central galaxy to distances greater than 1.5 Mpc within the cluster, and intermittent jets are able to distribute the metals to larger radii than the continuous jets. The metal injection affects the general ICM metal abundances, while the galaxy metal distribution details have no effect on the dynamical evolution of the ICM metals. We find metallicity gradients similar to those observed out to ∼ 400 kpc radii.

'The State of the Universe' - Stephen Hawking 70th Birthday Conference/Symposium

'The State of the Universe' scientific conference and the public symposium were held in Cambridge UK, to celebrate the 70th birthday of Professor Stephen Hawking. The conference was hosted by the Centre for Theoretical Cosmology (DAMTP) at the Centre for Mathematical Sciences in the University of Cambridge. We were very pleased to be able to hold this remarkable event for Professor Hawking, whose courage, insight and vision continues to have such an impact on the way we all understand fundamental physics at the extremes in black holes and the Big Bang. A major goal of the event was to review the current status of the fields of black holes, cosmology and fundamental physics; the 27 invited speakers are all world leaders in these fields.