Dynamics of a Dark Matter Field with a Quartic Self-Interaction Potential

It may prove useful in cosmology to understand the behavior of the energy distribution in a scalar field that interacts only with gravity and with itself by a pure quartic potential, because if such a field existed it would be gravitationally produced, as a squeezed state, during inflation. It is known that the mean energy density in such a field after inflation varies with the expansion of the universe in the same way as radiation. I show that if the field initially is close to homogeneous, with small energy density contrast delta rho /rho and coherence length L, the energy density fluctuations behave like acoustic oscillations in an ideal relativistic fluid for a time on the order of L/|delta rho /rho|. This ends with the appearance of features that resemble shock waves, but interact in a close to elastic way that reversibly disturbs the energy distribution.Comment: 7 pages, 5 figures, submitted to Phys Rev

Interaction between Faraday rotation and Cotton-Mouton effects in polarimetry modeling for NSTX

The evolution of electromagnetic wave polarization is modeled for propagation in the major radial direction in the National Spherical Torus Experiment (NSTX) with retroreflection from the center stack of the vacuum vessel. This modeling illustrates that the Cotton-Mouton effect-elliptization due to the magnetic field perpendicular to the propagation direction-is shown to be strongly weighted to the high-field region of the plasma. An interaction between the Faraday rotation and Cotton-Mouton effects is also clearly identified. Elliptization occurs when the wave polarization direction is neither parallel nor perpendicular to the local transverse magnetic field. Since Faraday rotation modifies the polarization direction during propagation, it must also affect the resultant elliptization. The Cotton-Mouton effect also intrinsically results in rotation of the polarization direction, but this effect is less significant in the plasma conditions modeled. The interaction increases at longer wavelength, and complicates interpretation of polarimetry measurements.Comment: Contributed paper published as part of the Proceedings of the 18th Topical Conference on High-Temperature Plasma Diagnostics, Wildwood, New Jersey, May, 201

Wheeler-DeWitt Quantization of Gravity Models of Unified Dark Energy and Dark Matter

First, we describe the construction of a new type of gravity-matter models based on the formalism of non-Riemannian space-time volume forms - alternative generally covariant integration measure densities (volume elements) defined in terms of auxiliary antisymmetric tensor gauge fields. Here gravity couples in a non-conventional way to two distinct scalar fields providing a unified Lagrangian action principle description of: (i) the evolution of both "early" and "late" Universe - by the "inflaton" scalar field; (ii) dark energy and dark matter as a unified manifestation of a single material entity - the "darkon" scalar field. A physically very interesting phenomenon occurs when including in addition interactions with the electro-weak model bosonic sector - we obtain a gravity-assisted dynamical generation of electro-weak spontaneous gauge symmetry breaking in the post-inflationary "late" Universe, while the Higgs-like scalar remains massless in the "early" Universe. Next, we proceed to the Wheeler-DeWitt minisuperspace quantization of the above models. The "darkon" field plays here the role of cosmological "time". In particular, we show the absence of cosmological space-time singularities.Comment: 15 pages, to be published in the Proceedings of QTS10 - 10th International Symposium "Quantum Theory and Symmetries" (Varna, 2017), Springer Proceedings in Mathematics and Statistics, V. Dobrev (ed.). arXiv admin note: text overlap with arXiv:1609.0691

Issues for the Next Generation of Galaxy Surveys

I argue that the weight of the available evidence favours the conclusions that galaxies are unbiased tracers of mass, the mean mass density (excluding a cosmological constant or its equivalent) is less than the critical Einstein-de Sitter value, and an isocurvature model for structure formation offers a viable and arguably attractive model for the early assembly of galaxies. If valid these conclusions complicate our work of adding structure formation to the standard model for cosmology, but it seems sensible to pay attention to evidence.Comment: 14 pages, 3 postscript figures, uses rspublic.st

Direct Detection Rates of Dark Matter Coupled to Dark Energy

We investigate the effect of a coupling between dark matter and dark energy on the rates for the direct detection of dark matter. The magnitude of the effect depends on the strength $\kappa$ of this new interaction relative to gravity. The resulting isothermal velocity distribution for dark matter in galaxy halos is still Maxwell-Boltzmann (M-B), but the characteristic velocity and the escape velocity are increased by $\sqrt{1+\kappa^2}$. We adopt a phenomenological approach and consider values of $\kappa$ near unity. For such values we find that: (i) The (time averaged) event rate increases for light WIMPs, while it is somewhat reduced for WIMP masses larger than 100 GeV. (ii) The time dependence of the rate arising from the modulation amplitude is decreased compared to the standard M-B velocity distribution. (iii) The average and maximum WIMP energy increase proportionally to $1+\kappa^2$, which, for sufficiently massive WIMPs, allows the possibility of designing experiments measuring $\gamma$ rays following nuclear de-excitation.Comment: 16 pages, 7 figure

Direct Determinations of the Redshift Behavior of the Pressure, Energy Density, and Equation of State of the Dark Energy and the Acceleration of the Universe

One of the goals of current cosmological studies is the determination of the expansion and acceleration rates of the universe as functions of redshift, and the determination of the properties of the dark energy that can explain these observations. Here the expansion and acceleration rates are determined directly from the data, without the need for the specification of a theory of gravity, and without adopting an a priori parameterization of the form or redshift evolution of the dark energy. We use the latest set of distances to SN standard candles from Riess et al. (2004), supplemented by data on radio galaxy standard ruler sizes, as described by Daly and Djorgovski (2003, 2004). We find that the universe transitions from acceleration to deceleration at a redshift of about 0.4. The standard "concordance model" provides a reasonably good fit to the dimensionless expansion rate as a function of redshift, though it fits the dimensionless acceleration rate as a function of redshift less well. The expansion and acceleration rates are then combined with a theory of gravity to determine the pressure, energy density, and equation of state of the dark energy as functions of redshift. Adopting General Relativity as the correct theory of gravity, the redshift trends for the pressure, energy density, and equation of state of the dark energy out to redshifts of about one are determined, and are found to be generally consistent with the concordance model.Comment: 8 pages, 5 figures. Invited presentation at Coral Gables 200

Limits on the integration constant of the dark radiation term in Brane Cosmology

We consider the constraints from primordial Helium abundances on the constant of integration of the dark radiation term of the brane-world generalized Friedmann equation derived from the Randall-Sundrum Single brane model. We found that -- using simple, approximate and semianalytical Method -- that the constant of integration is limited to be between -8.9 and 2.2 which limits the possible contribution from dark radiation term to be approximately between -27% to 7% of the background photon energy density.Comment: 8 page

Properties of voids in the Local Volume

Current explanation of the overabundance of dark matter subhalos in the Local Group (LG) indicates that there maybe a limit on mass of a halo, which can host a galaxy. This idea can be tested using voids in the distribution of galaxies: at some level small voids should not contain any (even dwarf) galaxies. We use observational samples complete to M_B=-12 with distances less than 8 Mpc to construct the void function (VF): the distribution of sizes of voids empty of any galaxies. There are ~ 30 voids with sizes ranging from 1 to 5 Mpc. We also study the distribution of dark matter halos in very high resolution simulations of the LCDM model. The theoretical VF matches the observations remarkably well only if we use halos with circular velocities larger than 45 +/- 10 km/s. This agrees with the Local Group predictions. Small voids look quite similar to heir giant cousins: the density has a minimum at the center of a void and it increases as we get closer to the border. Thus, both the Local Group data and the nearby voids indicate that isolated halos below 45 +/- 10 km/s must not host galaxies and that small (few Mpc) voids are truly dark.Comment: 5 pages 1 figure. To appear in proceedings of the conference "Galaxies in the Local Volume", Sydney, 8 to 13 July 200

New Constraints on the Variable Equation of State Parameter from X-Ray Gas Mass Fractions and SNe Ia

Recent measurements are suggesting that we live in a flat Universe and that its present accelerating stage is driven by a dark energy component whose equation of state may evolve in time. Assuming two different parameterizations for the function $\omega(z)$, we constrain their free parameters from a joint analysis involving measurements from X-Ray luminosity of galaxy clusters and SNe type Ia data.Comment: paper, 6 pages, 1 figure Accepted by Int. Journal of Modern Physics D (IJPMD

Galaxy Satellites and the Weak Equivalence Principle

Numerical simulations of the effect of a long-range scalar interaction (LRSI) acting only on nonbaryonic dark matter, with strength comparable to gravity, show patterns of disruption of satellites that can agree with what is seen in the Milky Way. This includes the symmetric Sagittarius stellar stream. The exception presented here to the Kesden and Kamionkowski demonstration that an LRSI tends to produce distinctly asymmetric streams follows if the LRSI is strong enough to separate the stars from the dark matter before tidal disruption of the stellar component, and if stars dominate the mass in the luminous part of the satellite. It requires that the Sgr galaxy now contains little dark matter, which may be consistent with the Sgr stellar velocity dispersion, for in the simulation the dispersion at pericenter exceeds virial. We present other examples of simulations in which a strong LRSI produces satellites with large mass-to-light ratio, as in Draco, or free streams of stars, which might be compared to "orphan" streams.Comment: 14 pages, accepted for publication in PR