Magic Monday Journal Club

10th February 2014

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A Journal Club where the more fundamental news we learnt was that .. Einstein was human...

And can sometimes make mistakes of factor 3 in his equations.


by I Lopes, P. Panci, J. Silk

Apparently, there's a huge discrepancy between predictions of the standard solar model and observations concerning the speed of sound wave propagation inside the Sun.  This paper studies whether the tension can be ameliorated by dark matter in the Sun that interacts with baryons via a ligt (MeV-ish) mediator. The result is that with this dark matter model one can obtain a better fit, although one cannot fully explain the data.

Selectron/smuon NLSP in Gauge mediation

By L. Calibbi

Lorenzo came from Brussels (again, this city furnish a lot of physicists and even.. Nobel prizes nowadays) to discuss about his last work (before publication) concerning selectron and smuon searches and limits one can obtain when we suppose that they are the NLSP (lighter than the stau so) in Gauge mediation scenario. You can find his slide there.

AMS02 data confronts acceleration of cosmic ray secondaries in nearby sources

by P. Mertsch and S. Sarkar

I would say that this can close definitively the Dark Matter chapter of positron excess from PAMELA or AMS02. Sarkar shows in this paper that not only «classical» models of supernovae remnants (SNR) can fit perfectly the positron excess and its spectrum but also the boron-to-carbon ratio and the absolute flux of Helium measured also by AMS-02. It also fit the proton-antiproton ratio given by PAMELA (waiting for the one measured by AMS-02). If the later fits with their Fig.5, I think the positron book can come to a nice astrophysical explanation.  Just a look at their Fig.1 should be sufficient for the ones who just want to discuss it at the cafeteria with their best friend.  You can find an annotated version of the paper here.

γ-ray anisotropies from dark matter in the Milky Way: the role of the radial distribution

by F. Calore1, V. De Romeri, M. Di Mauro, F. Donato, J. Herpich, A.V. Macciò, L. Maccione

In this (almost) italian work, they compute the perspective of discovery of dark matter halo and subhalo, looking at the anisotropies measured by FERMI. Depending on  the dark matter profile in the smooth halo and in some satellites clumps they find that the smooth halo dominate the angular power spectrum up to quite large multipoles, where the subhaloes anisotropy signal starts to emerge. A nice view of the sky can be seen at their Figures 2, whereas for people who wants to make a little brain-gymnastic, look at their Fig.3, all is summarized there. To remind you, l (multipole) > 500 probes radius < π/500 * 8.8 pc = 40 pc. You can find an annotated version of the paper here.

Observables for model-independent detections of Z′ boson at the ILC

by V. Skalozub and I. Kucher

In this original work, the Ukranian authors proposed a way to discriminate different Z’ models at LHC. Their main idea is to look at a leptonic final state, and under the geenral considerations of (V-A) couplings, to find the best region of integration on the scattering angle to extract combinations of couplings that they can then determined. The paper is strangely written, the figures are terrible, but the results interesting. Look at their equations (5), (7), (8) and (9) [in this order] and you will understand their philosophy. An annotated version of the paper is hidden there.

Early Results from the Qweak Experiment

Qweak collaboration

By measuring the weak charge of nuclei one can probe parity-violating effective  4-fermion operators involving quarks and electrons. The QWEAK experiment measures the weak charge of the proton by measuring the polarization asymmetry of electron scattering on liquid hydrogen. Current constraints on the scale suppressing the parity violating qqee operators is in the 3 TeV ballpark.

On Z → γ γ  decay and cancellation of axial anomaly in Z → γ γ transition amplitude for massive fermions

by E.V. Zhemchugov

I don’t really know who is this guy from Moscow, but his stage supervisor gave him a hard work. This student just computed the Z -> γ γ amplitude in Standard Model framework, taking into account subtleties that seemed to have been forgotten in precedding studies (like ensuring Ward identities AFTER the Feynman integration) It is really a nice job that anyone interesting in teaching anomalies and especially the Landau-Yang  theorem should read. Very instructive work. You can find an annotated version here.

The Steady-State theory of the Expanding Universe

by H. Bondi and T. Gold


This is the first article proposing a solution to the Hubble expansion of the Universe different that the one proposed by Gamow et al., especially concerning the BBN and matter creation. Indeed, the observations of Hubble was given a too young Universe compared to radioactive measurements of rocks on earth. until the 60’s, this model was competing with the Big Bang theory until the measurement of age of nearby galaxies and pulsars (and the CMBN measurement of course) throw the model in the trash of «good ideas / bad data». It is interesting to note that Einstein proposed something similar in a non-published draft in 1931. Look there by curiosity.