Munch: Monday, November 27, 2006

                               


 

    usual time and place:  12:30, 6th floor conference room

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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       Munch Archive

Tests of the Gravitational Inverse-Square Law below the Dark-Energy Length Scale

Authors: D.J. Kapner, T.S. Cook, E.G. Adelberger, J.H. Gundlach, B.R. Heckel, C.D. Hoyle, H.E. Swanson
Comments: 4 pages, 6 figures
We conducted three torsion-balance experiments to test the gravitational inverse-square law at separations between 9.53 mm and 55 micrometers, probing distances less than the dark-energy length scale $\lambda_{\rm d}=\sqrt[4]{\hbar c/\rho_{\rm d}}\approx 85 \mu$m. We find with 95% confidence that the inverse-square law holds ($|\alpha| \leq 1$) down to a length scale $\lambda = 56 \mu$m and that an extra dimension must have a size $R \leq 44 \mu$m.

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Constraints on Exotic Interactions from a Recent Test of the Gravitational Inverse Sqaure Law

Authors: E.G. Adelberger, B.R. Heckel, S. Hoedl, C.D. Hoyle, D.J. Kapner
Comments: 4 pages, 5 figures
We use data from our recent search for violations of the gravitational inverse-square law to constrain dilaton, radion and chameleon exchange forces as well as arbitrary vector or scalar interactions. We test the interpretation of the PVLAS effect and a conjectured ``fat graviton'' scenario and constrain the $\gamma_5$ couplings of pseuodscalar bosons and arbitrary power-law interactions.

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A new scale in the sky

Authors: M. Gasperini
Comments: 6 pages, 2 figures included with epsfig. Essay written for the 2006 Awards for Essays on Gravitation (Gravity Research Foundation), and awarded with "Honorable Mention". To appear in Int. J Mod. Phys. D (December 2006, Special Issue)
Report-no: CERN-PH-TH/2006-031
The existence of a new ultraviolet scale $\Lambda=g M_P$ for effective theories with gravity and U(1) gauge fields has recently been conjectured as a possible criterion for distinguishing parts of the swampland from the string landscape. Here we discuss a possible phenomenological signature of this scale, for electromagnetic fields, in astrophysical observations.

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Cosmology with the Planck cluster sample

Authors: Joern Geisbuesch, Michael Hobson
Comments: 20 pages, 9 figures, submitted to MNRAS
It has been long recognised that, besides being a formidable experiment to observe the primordial CMB anisotropies, Planck will also have the capability to detect galaxy clusters via their SZ imprint. In this paper constraints on cosmological parameters derivable from the Planck cluster candidate sample are examined for the first time as a function of cluster sample selection and purity obtained from realistic simulations of the microwave sky at the Planck observing frequency bands, observation process modelling and a cluster extraction pipeline. In particular, we employ a multi-frequency matched filtering (MFMF) method to recover clusters from mock simulations of Planck observations. Obtainable cosmological constraints under realistic assumptions of priors and knowledge about cluster redshifts are discussed. Just relying on cluster redshift abundances without making use of recovered cluster fluxes, it is shown that from the Planck cluster catalogue cosmological constraints comparable to the ones derived from recent primordial CMB power spectrum measurements can be achieved. For example, for a concordance $\Lambda$CDM model and a redshift binning of $\Delta z = 0.1$, the $1\sigma$ uncertainties on the values of $\Omega_m$ and $\sigma_8$ are $\Delta \Omega_m \approx 0.031$ and $\Delta \sigma_8 \approx 0.014$ respectively. Furthermore, we find that the constraint of the matter density depends strongly on the prior which can be imposed on the Hubble parameter by other observational means.

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Dark Antimatter as a Galactic Heater: X-rays from the Core of our Galaxy

Authors: Michael McNeil Forbes, Ariel R. Zhitnitsky
Comments: 4 pages, REVTeX4
Report-no: NT@UW-06-25
Several independent observations of the Galactic core suggest hitherto unexplained sources of energy. We show that dark matter in the form of dense antimatter droplets provides a natural site for electron and proton annihilation, providing 511 keV photons, gamma-rays, and energy that sustains thermal X-ray radiation. Such a picture not only identifies the dark matter in our universe, but allows X-ray observations to directly probe the matter distribution in our Galaxy.

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The Axis of Evil revisited

Authors: Kate Land, Joao Magueijo
Comments: 5 pages, submitted to MNRAS
In light of the three-year data release from WMAP we re-examine the evidence for the ``Axis of Evil''. We discover that previous frequentist methods are not robust with respect to the data-sets available and different treatments of the galactic plane. We identify the cause of the instability and show that this result is not a weakness of the data. This is further confirmed by exhibiting an alternative approach, Bayesian in flavour, and based on a likelihood method and the information criteria. We find strong (and sometimes decisive) evidence for the ``Axis of Evil'' in almost all renditions of the WMAP data. However some significant differences between data-sets remain, and the quantitative aspects of the result depend on the particular information criteria used.

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Dodecahedral topology fails to explain quadrupole-octupole alignment

Authors: Jeff Weeks, Jesper Gundermann
Comments: 5 pages, 1 figure
The CMB quadrupole and octupole, as well as being weaker than expected, align suspiciously well with each other. Non-trivial spatial topology can explain the weakness. Might it also explain the alignment? The answer, at least in the case of the Poincare dodecahedral space, is a resounding no.

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Large Non-Gaussianities in Single Field Inflation

Authors: Xingang Chen, Richard Easther, Eugene A. Lim
Comments: 23 pages JHEP-style, 8 Figures
We compute the 3-point correlation function for a general model of inflation driven by a single, minimally coupled scalar field. Our approach is based on the numerical evaluation of both the perturbation equations and the integrals which contribute to the 3-point function. Consequently, we can analyze models where the potential has a "feature", in the vicinity of which the slow roll parameters may take on large, transient values. This introduces both scale and shape dependent non-Gaussianities into the primordial perturbations. As an example of our methodology, we examine the ``step'' potentials which have been invoked to improve the fit to the glitch in the $<TT>$ $C_l$ for $l \sim 30$, present in both the one and three year WMAP data sets. We show that for the typical parameter values, the non-Gaussianities associated with the step are far larger than those in standard slow roll inflation, and may even be within reach of a next generation CMB experiment such as Planck. More generally, we use this example to explain that while adding features to potential can improve the fit to the 2-point function, these are generically associated with a greatly enhanced signal at the 3-point level. Moreover, this 3-point signal will have a very nontrivial shape and scale dependence, which is correlated with the form of the 2-point function, and may thus lead to a consistency check on the models of inflation with non-smooth potentials.

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