Magic Monday Journal Club

21st October 2013

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An Equivalent Gauge and Equivalence Theorem

by A. Wulzer

The equivalence theorem relates the scattering amplitude of longitudinally polarized massive vector bosons to those of the eaten Goldstone bosons. This  allows one to understand more easily the high energy behavior  of these amplitudes, which in a spontaneously broken gauge theory involve non-trivial cancellations of terms growing with energy. The paper finds a gauge where  the longitudinal polarization vectors do not grow with the energy, and the equivalence theorem (together with its limitations) becomes

manifest. The paper is very pedagogical, almost like a textbook material, and offers some insight into quantization of gauge theories.

Implication of neutrino background on the reach of next generation dark matter direct detection experiment

by J. Billard, E. Figueroa-Feliciano and L. Strigari

In this interesting paper, the authors compute the expected signal given by neutrino background on direct detection experiments. They took into account atmospheric, solar and neutrino from diffuse supernovae to cover a large spectrum of energy of recoil. They show that below a cross section of about  10^-47 to 10^-50 cm2 it will be impossible to distinguish a neutrono from a dark matter candidate. Very nice paper. Jump on their Fig.12 it is a great summary of their work.  You can find the annoted version of the paper here.

Discovering the significance of 5σ

by L. Lyons

In this original paper, Louis Lyons discuss the pertinence to take as a discovery criteria the 5σ limit and shows that ifor each cases, depending on systematic or need for looke elsewhere effects, one should be more precautious and less strict, adapting the definition of «discovery» to each type of experiments or field of research. You can find the annoted version of the paper here.

Neutrino at Icecube from heavy decaying dark matter

by B. Feldstein, A. Kusenko, S. Matsumoto and T. Yanagida

The authors show that the 2 PeV icecube events can be interpreted in term of decaying dark matter corresponding to a lifetime of about 10^28 seconds and a 2.4 PeV DM. They first constraints models with an effective approach and then applied it to two kinds of extensions : heavy Z’ and gravitino dark matter.  It can works in both cases, requiring a R-parity violation coupling for the gravitino (of course!!). However, in this case, the expected lifetime of the gravitino is 10^20 seconds, so other suppression mechanisms (generated by B-L symmetry) are needed. In the case of massive Z’, the Icecube flux is more naturally obtained. They also look at the continuum that should be present in any case. You can find the annoted version of the paper here.

On the constitution of Atoms and Molecules

by N. Bohr (1913)

Bohr met Rutherford in November 1911 while working with J.J. Thomson. This encounters gave rise to one of the most unexcpected colaboration of friendship that will last all their life. Bohr was as we can call now a «post-doc» with a one year fellowship, and he decided to spend its 4 last months in Manchester with Rutherford. Combining the ideas of Planck and the atomic proposition of Rutherford, he then developped the first quantum model of atoms for which he will receive the Nobel prize in 1922.  You can find the original paper here.