Munch: Monday, January 29, 2007

                               


 

 WHERE: 6TH FLOOR CONFERENCE ROOM
WHEN  : 12:30, MONDAY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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       Munch Archive

Cosmological neutrino mass detection: The best probe of neutrino lifetime            astro-ph/0701699 (suggested by Einstein)

Authors: Pasquale D. Serpico
Comments: 4 pages, 1 eps figure
Report-no: FERMILAB-PUB-07-015-A
Future cosmological data may be sensitive to the effects of a finite neutrino mass even as small as the ~0.05 eV lower limit guaranteed by neutrino oscillation experiments. We show that a cosmological detection of neutrino mass in agreement with expectations would improve by many orders of magnitude the existing limits on neutrino lifetime, and as a consequence on neutrino secret interactions with (quasi-)massless particles as in majoron models. On the other hand, neutrino decay may provide a way-out to explain a discrepancy between cosmic neutrino bounds and Lab data.

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The Einstein-Elko system -- Can dark matter drive inflation?  gr-qc/0701087  (suggested by Mark)

Authors: C. G. Boehmer
Comments: 24 pages
Recently, a spin one half matter field with mass dimension one was discovered, called Elko spinors. The present work shows how to introduce these fields into a curved spacetime by the standard covariantisation scheme. After formulating the coupled Einstein-Elko field equations, the spacetime is assumed to be homogeneous and isotropic in order to simplify the resulting field equations. Analytical ghost Elko solutions are constructed which have vanishing energy-momentum tensor without and with cosmological constant. The cosmological Elko theory is finally related to the standard scalar field theory with self interaction that gives rise to inflation and it is pointed out that the Elko spinors are not only prime dark matter candidates but also prime candidates for inflation.

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Determining the Nature of Dark Matter with Astrometry                                  astro-ph/0701581 (suggested by Scott)

Authors: Louis E. Strigari, James S. Bullock, Manoj Kaplinghat
Comments: Accepted for publication in ApJL
We show that measurements of stellar proper motions in dwarf spheroidal galaxies provide a powerful probe of the nature of dark matter. Allowing for general dark matter density profiles and stellar velocity anisotropy profiles, we show that the log-slope of the dark matter profile at about twice the stellar core (King) radius can be measured to within \pm 0.2 when the proper motions of 200 stars are added to standard line-of-sight velocity dispersion data. This measurement of the log-slope provides a test of Cold and Warm Dark Matter theories at a sensitivity not possible with line-of-sight velocity dispersion measurements alone. The upcoming SIM PlanetQuest will have the sensitivity to obtain the required number of proper motions in Milky Way dwarf spheroidal galaxies.

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Resonantly Enhanced Axion-Photon Regeneration                                          hep-ph/0701198 (suggested by Pasquale)

Authors: P. Sikivie, D.B. Tanner, Karl van Bibber
Comments: 4 pages, 2 figures
Report-no: UFIFT-HEP-07-1, UCRL-JRNL-227149
We point out that photon regeneration-experiments that search for the axion, or axion-like particles, may be resonantly enhanced by employing matched Fabry-Perot optical cavities encompassing both the axion production and conversion magnetic field regions. Compared to a simple photon regeneration experiment, which uses the laser in a single-pass geometry, this technique can result in a gain in rate of order ${\cal F}^2$, where ${\cal F}$ is the finesse of the cavities. This gain could feasibly be $10^{(10-12)}$, corresponding to an improvement in sensitivity in the axion-photon coupling, $g_{a\gamma\gamma}$ , of order ${\cal F}^{1/2} \sim 10^{(2.5-3)}$, permitting a practical purely laboratory search to probe axion-photon couplings not previously excluded by stellar evolution limits, or solar axion searches.

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Imprints of a Primordial Preferred Direction on the Microwave Background astro-ph/0701357  (suggested by Dan)

Authors: Lotty Ackerman, Sean M. Carroll, Mark B. Wise
Comments: 7 pages, no figures
Report-no: CALT-68-2626
Rotational invariance is a well-established feature of low-energy physics. Violations of this symmetry must be extremely small today, but could have been larger in earlier epochs. In this paper we examine the consequences of a small breaking of rotational invariance during the inflationary era when the primordial density fluctuations were generated. Assuming that a fixed-norm vector picked out a preferred direction during the inflationary era, we explore the imprint it would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes $<a_{lm}a_{l'm'}^*>$ of the spherical-harmonic coefficients. We suggest that it is natural to expect that the imprint on the primordial power spectrum of a preferred spatial direction is approximately scale-invariant, and examine a simple model in which this is true.

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Can large-scale structure probe CMB-constrained non-Gaussianity?        astro-ph/0701131 (suggested by Emiliano)

Authors: X. Kang, P. Norberg, J. Silk
Comments: 5 Pages, 5 Figures; accepted for publication in MNRAS
The first year Wilkinson Microwave Anisotropy Probe (WMAP) set quantitative constraints on the amplitude of any primordial non-Gaussianity. We run a series of dark matter-only N-body simulations with the WMAP constraints to investigate the effect of the presence of primordial non-Gaussianity on large scale structures. The model parameters can be constrained using the observations of protoclusters associated with Ly-$\alpha$ emitters at high redshift ($2 \leq z \leq 4$), assuming the galaxy velocity bias can be modelled properly. High redshift structure formation potentially provides a more powerful test of possible primordial non-Gaussianity than does the CMB, albeit on smaller scales. Another constraint is given by the local galaxy density probability distribution function (PDF), as mapped by the 2 degree Field Galaxy Redshift Survey (2dFGRS). The PDF of 2dFGRS \lstar galaxies is substantially higher than the standard model predictions and requires either a non-negligible bias between galaxy and dark matter on $\sim 12$~\hmpc scales or a stronger non-Gaussianity than allowed by the WMAP year one data. The latter interpretation is preferred since second-order bias corrections are negative. With a lower normalisation of the power spectrum fluctuations, sigma_8=0.74, as favoured by the WMAP 3 year data, the discrepancy between the Gaussian model and the data is even larger.

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Dark matter from late decays and the small-scale structure problems         hep-ph/0701007 (suggested by Dan)

Authors: Torsten Bringmann, Francesca Borzumati, Piero Ullio
Comments: 15 pages revtex4 style; 10 figures
The generation of dark matter in late decays of quasi-stable massive particles has been proposed as a viable framework to address the excess of power found in numerical N-body simulations for cold dark matter cosmologies. We identify a convenient set of variable to illustrate which requirements need to be satisfied in any generic particle physics model to address the small scale problems and fulfill other astrophysical constraints. We re-examine the role of gravitinos and Kaluza-Klein gravitons in this context and find them disfavoured as a solution to the small-scale problems in case they are DM candidates generated in the decay of thermally produced WIMPs. We propose right-handed sneutrinos and right-handed Kaluza-Klein neutrinos as alternatives. We find that they are viable dark matter candidates, but that they can contribute to a solution of the small scale problems only in case the associated Dirac neutrino mass term appears as a subdominant contribution in the neutrino mass matrix.

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Dark energy from cosmological neutrino condensation                                astro-ph/0701212 (suggested by Scott)

Authors: H. J. de Vega
Comments: 25 pages, 2 figures
We show here that cosmological neutrino condensation provides a continuous energy distribution able to reproduce the observed dark energy. The neutrino evolution is solved as a field theory initial value problem in cosmological spacetime for times after neutrino decoupling. Physical quantities are subtracted in order to eliminate ultraviolet divergences. The subtractions respect the symmetries of the theory and we normalize them such that the physical quantities are zero in Minkowski space-time.The lightest neutrino mass has to be 0.0033 eV for Dirac neutrinos [and 0.0039 eV for Majorana neutrinos] in order to reproduce the observed dark energy.The two heavier neutrinos should annihilate with their respective anti-neutrinos in the time scale of the age of the universe. We find a dark matter equation of state with a logarithmic dependence in the redshift w(z) = -1 - 1/\{3 [21.8 - log(1+z)]} and w(0) = -1.015...These formulas only depend on the ratio of the neutrino temperatures at decoupling and today. Dark energy arises from neutrino condensation in FRW cosmological space-time in an analogous way to the Casimir effect in Minkowski space-time with non-trivial boundaries.

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Hints of Isocurvature Perturbations in the Cosmic Microwave Background  astro-ph/0611917 (suggested by Pasquale)

Authors: Reijo Keskitalo (HIP and Helsinki U.), Hannu Kurki-Suonio (Helsinki U.), Vesa Muhonen (HIP and Helsinki U.), Jussi Valiviita (ICG, Portsmouth)
Comments: 4 pages, 2 figures, revtex4 format
Report-no: HIP-2006-52/TH, ICG 06/43
The improved data on the cosmic microwave background (CMB) anisotropy allows a better determination of the adiabaticity of the primordial perturbation. Interestingly, we find that the CMB favors a significant contribution of a primordial isocurvature mode where the entropy perturbation is positively correlated with the primordial curvature perturbation and has a large spectral index (n_iso ~ 3). With 4 additional parameters we obtain a better fit to the CMB data by \Delta\chi^2 = 9.4 compared to an adiabatic model. At more than 95% C.L., the nonadiabatic contribution to the CMB temperature variance is nonzero; indeed positive. For the best-fit model it is 4%.

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