Rippled Cosmological Dark Matter from Damped Oscillating Newton Constant

Let the reciprocal Newton 'constant' be an apparently non-dynamical Brans-Dicke scalar field damped oscillating towards its General Relativistic VEV. We show, without introducing additional matter fields or dust, that the corresponding cosmological evolution averagely resembles, in the Jordan frame, the familiar dark radiation -> dark matter -> dark energy domination sequence. The fingerprints of our theory are fine ripples, hopefully testable, in the FRW scale factor; they die away at the General Relativity limit. The possibility that the Brans-Dicke scalar also serves as the inflaton is favorably examined.Comment: RevTex4, 12 pages, 5 figures; Minor revision, References adde

Sigma-Model Aether

Theories of low-energy Lorentz violation by a fixed-norm "aether" vector field with two-derivative kinetic terms have a globally bounded Hamiltonian and are perturbatively stable only if the vector is timelike and the kinetic term in the action takes the form of a sigma model. Here we investigate the phenomenological properties of this theory. We first consider the propagation of modes in the presence of gravity, and show that there is a unique choice of curvature coupling that leads to a theory without superluminal modes. Experimental constraints on this theory come from a number of sources, and we examine bounds in a two-dimensional parameter space. We then consider the cosmological evolution of the aether, arguing that the vector will naturally evolve to be orthogonal to constant-density hypersurfaces in a Friedmann-Robertson-Walker cosmology. Finally, we examine cosmological evolution in the presence of an extra compact dimension of space, concluding that a vector can maintain a constant projection along the extra dimension in an expanding universe only when the expansion is exponential.Comment: 8 pages, 2 figures; fixed minor typo and changed references in v

Solution of the dispersionless Hirota equations

The dispersionless differential Fay identity is shown to be equivalent to a kernel expansion providing a universal algebraic characterization and solution of the dispersionless Hirota equations. Some calculations based on D-bar data of the action are also indicated.Comment: Late

Fine Tuning Free Paradigm of Two Measures Theory: K-Essence, Absence of Initial Singularity of the Curvature and Inflation with Graceful Exit to Zero Cosmological Constant State

The dilaton-gravity sector of the Two Measures Field Theory (TMT)is explored in detail in the context of cosmology. The model possesses scale invariance which is spontaneously broken due to the intrinsic features of the TMT dynamics. The effective model represents an explicit example of the effective k-essence resulting from first principles without any exotic term in the fundamental action. Depending of the choice of regions in the parameter space, TMT exhibits different possible outputs for cosmological dynamics: a) Absence of initial singularity of the curvature while its time derivative is singular. This is a sort of "sudden" singularities studied by Barrow on purely kinematic grounds. b) Power law inflation in the subsequent stage of evolution. Depending on the region in the parameter space (but without fine tuning) the inflation ends with a graceful exit either into the state with zero cosmological constant (CC) or into the state driven by both a small CC and the field phi with a quintessence-like potential. c) Possibility of resolution of the old CC problem. From the point of view of TMT, it becomes clear why the old CC problem cannot be solved (without fine tuning) in conventional field theories. d) TMT enables two ways for achieving small CC without fine tuning of dimensionfull parameters: either by a seesaw type mechanism or due to a correspondence principle between TMT and conventional field theories (i.e theories with only the measure of integration sqrt{-g} in the action. e) There is a wide range of the parameters such that in the late time universe: the equation-of-state w=p/\rho <-1; w asymptotically (as t\to\infty) approaches -1 from below; \rho approaches a constant, the smallness of which does not require fine tuning of dimensionfull parameters.Comment: 37 pages, 20 figures. Minor misprints corrected, reference added. The final version published in Phys. Rev.

The extended Malkus-Robbins dynamo as a perturbed Lorenz system

Recent investigations of some self-exciting Faraday-disk homopolar dynamo ([1-4]) have yielded the classic Lorenz equations as a special limit when one of the principal bifurcation parameters is zero. In this paper we focus upon one of those models [3] and illustrate what happens to some of the lowest order unstable periodic orbits as this parameter is increased from zero

Mapping EK Draconis with PEPSI - Possible evidence for starspot penumbrae

We present the first temperature surface map of EK Dra from very-high-resolution spectra obtained with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope. Changes in spectral line profiles are inverted to a stellar surface temperature map using our $i$Map code. The long-term photometric record is employed to compare our map with previously published maps. Four cool spots were reconstructed, but no polar spot was seen. The temperature difference to the photosphere of the spots is between 990 and 280K. Two spots are reconstructed with a typical solar morphology with an umbra and a penumbra. For the one isolated and relatively round spot (A), we determine an umbral temperature of 990K and a penumbral temperature of 180K below photospheric temperature. The umbra to photosphere intensity ratio of EK Dra is approximately only half of that of a comparison sunspot. A test inversion from degraded line profiles showed that the higher spectral resolution of PEPSI reconstructs the surface with a temperature difference that is on average 10% higher than before and with smaller surface areas by 10-20%. PEPSI is therefore better suited to detecting and characterising temperature inhomogeneities. With ten more years of photometry, we also refine the spot cycle period of EK Dra to 8.9$\pm$0.2 years with a continuing long-term fading trend. The temperature morphology of spot A so far appears to show the best evidence for the existence of a solar-like penumbra for a starspot. We emphasise that it is more the non-capture of the true umbral contrast rather than the detection of the weak penumbra that is the limiting factor. The relatively small line broadening of EK Dra, together with the only moderately high spectral resolutions previously available, appear to be the main contributors to the lower-than-expected spot contrasts when comparing to the Sun.Comment: Accepted for A&

Surveying the solar system by measuring angles and times: from the solar density to the gravitational constant

A surprisingly large amount of information on our solar system can be gained from simple measurements of the apparent angular diameters of the sun and the moon. This information includes the average density of the sun, the distance between earth and moon, the radius of the moon, and the gravitational constant. In this note it is described how these and other quantities can be obtained by simple earthbound measurements of angles and times only, without using any explicit information on distances between celestial bodies. The pedagogical and historical aspects of these results are also discussed briefly.Comment: 12 pges, one figur