Archive for November, 2011

Articles

23 November, 2011

In High Energy Physics on November 24, 2011 by physthjc

1) Presentation of  A. Tokareva’s work (visitor)

  • Positronium Oscillations to Mirror World revisited
    abstract:  We present a calculation of the branching ratio of orthopositronium decay into invisible mode, which is done in the context of Mirror World models, where ordinary positronium can disappear from our world due to oscillation into its mirror twin. In this revision we clarify some formulas and approximations used previously, correct them at some places, add new effects relevant for a feasible experiment and finally perform a combined analysis. We include into consideration various effects due to external magnetic and electric fields, collisions with cavity walls and scattering off gas atoms in the cavity. Oscillations of the Rydberg positroniums are also considered. To perform a numerical estimates in a realistic case we use the original computer code, which can be adopted to any experimental setup. Its work is illustrated with an example of planned positronium experiment within AEgIS project.

2) First result from Double Chooz experiment

3) Why Photons are not slow?

  • Abstract: In an attempt to reconcile the Opera experiment with Special relativity, we examine the possibility that the Special relativity formalism holds, but with a larger limiting speed cl , while the photon moves at slower speed (which may involve the presence of an ether). We show that even such a possibility is excluded by comparison with recent Michelson-Morley type experiments (except maybe in a very contrieved framework).

4) CP violation in charm decays at LHCb

5) Update on Opera result

  • “Following the OPERA collaboration’s presentation at CERN on 23 September, inviting scrutiny of their neutrino time-of-flight measurement from the broader particle physics community, the collaboration has rechecked many aspects of its analysis and taken into account valuable suggestions from a wide range of sources. One key test was to repeat the measurement with very short beam pulses from CERN. This allowed the extraction time of the protons, that ultimately lead to the neutrino beam, to be measured more precisely. The beam sent from CERN consisted of pulses three nanoseconds long separated by up to 524 nanoseconds. Some 20 clean neutrino events were measured at the Gran Sasso Laboratory, and precisely associated with the pulse leaving CERN. This test confirms the accuracy of OPERA’s timing measurement, ruling out one potential source of systematic error. The new measurements do not change the initial conclusion. Nevertheless, the observed anomaly in the neutrinos’ time of flight from CERN to Gran Sasso still needs further scrutiny and independent measurement before it can be refuted or confirmed. On 17 November, the collaboration submitted a paper on this measurement to the peer reviewed Journal of High Energy Physics (JHEP).” (CERN Press Release)

Articles

16 November, 2011

In High Energy Physics on November 17, 2011 by physthjc

1) Presentation of  Tiziana’s work

  • “We use a model independent approach in order to study the possibility
    of discriminating among the various effective operators producing a
    gamma line through 6-dimensional operators responsible for the decay
    of a generic dark matter. Using the constraints of PAMELA on the
    antiproton fraction, we check if the upper bounds on the intensity of
    the gamma line produced by the different types of operators could be
    more significant than the astrophysical uncertainties, allowing a
    distinction among some operators.”

2) Electroweak Baryogenesis

  • Supersonic Electroweak Baryogenesis: Achieving Baryogenesis for Fast Bubble Walls
    Abstract
     : Standard electroweak baryogenesis in the context of a first order phase transition is effective in generating the baryon asymmetry of the universe if the broken phase bubbles expand at subsonic speed, so that CP asymmetric currents can diffuse in front of the wall. Here we present a new mechanism for electroweak baryogenesis which operates for supersonic bubble walls. It relies on the formation of small bubbles of the symmetric phase behind the bubble wall, in the broken phase, due to the heating of the plasma as the wall passes by. We apply the mechanism to a model in which the Higgs field is coupled to several singlets, and find that enough baryon asymmetry is generated for reasonable values of the parameter space.

Articles

9 November, 2011

In High Energy Physics on November 10, 2011 by physthjc

1) Peculiar Motion of The Solar System

  • Large peculiar motion of the solar system from the dipole anisotropy in sky brightness due to distant radio sourcesAbstract : According to the cosmological principle, the Universe should appear isotropic, without any preferred directions, to an observer whom we may consider to be fixed in the co-moving co-ordinate system of the expanding Universe. Such an observer is stationary with respect to the average distribution of the matter in the Universe and the sky brightness at any frequency should appear uniform in all directions to such an observer. However a peculiar motion of such an observer, due to a combined effect of Doppler boosting and aberration, will introduce a dipole anisotropy in the observed sky brightness; in reverse an observed dipole anisotropy in the sky brightness could be used to infer the peculiar velocity of the observer with respect to the average Universe. We determine the peculiar velocity of the solar system relative to the frame of distant radio sources, by studying the anisotropy in the sky brightness from discrete radio sources, i.e., an integrated emission from discrete sources per unit solid angle. Our results give a direction of the velocity vector in agreement with the Cosmic Microwave Background Radiation (CMBR) value, but the magnitude ($\sim 1600\pm 400$ km/s) is $\sim 4$ times the CMBR value ($369\pm 1$ km/s) at a statistically significant ($\sim 3\sigma$) level. A genuine difference between the two dipoles would imply anisotropic Universe, with the anisotropy changing with the epoch. This would violate the cosmological principle where the isotropy of the Universe is assumed for all epochs, and on which the whole modern cosmology is based upon.
2) Presentation of the new postdoc Michel Gustafsson
3) Presentation of  Yong’s work
  • We consider the possibility that along the thermal history of the Universe, dark matter (DM) would have been created from SM particles either through a kinetic mixing portal to an extra U(1) gauge field, or through the Higgs portal. Depending solely on the size of the DM particle mass, of the portal and of an eventual DM hidden sector interaction, we show how the observed DM relic density can be obtained. There are four possible freeze-in/re-annihilation/freeze-out regimes, which results in a simple characteristic relic density phase diagram, with the shape of a “mesa”. In the case of the kinetic mixing portal, we show that, unlike other freeze-in scenarios discussed in the literature, the freeze-in regime can be probed by existing and forthcoming DM direct detection experiments. To illustrate these results we consider a particularly simple DM candidate, where DM consists in the lightest particle charged under a new unbroken U(1) gauge group. These results are well representative for any scenario where a hidden sector would be created out of the SM followed by the freezing of the DM relic abundance.