Magic Monday Journal Club

12th January 2015

Back to the  main page

 



Haaaa... The first MMJC of 2015. Some people considers that the «first time» is often the best one. Some not. In any case, who cares... The Journal club began by a nice photo-session of the holidays of your favorite magicians, so, for those who were absent this day «session de rattrapage» as we tell in French. Egypt and Thailand were the destinations of the Magic Globe trotters this year :










After this nice voyage par procuration, we decided to discuss these articles:


The Top Mass: Interpretation and Theoretical Uncertainties

by  A. H. Hoang


Measurements of the top quark mass quoted by experiments are really measurements of the PMAS(6,1) parameter in Pythia. Connecting this "monte carlo top mass" to the top Yukawa coupling  in the Lagrangian is non-trivial. This paper nicely reviews the subtleties involved in this matching. It looks like reducing the theoretical error for m_top measurements in hadron colliders below 1 GeV is not possible with current techniques. 


One-loop non-renormalization results in EFTs

by  J. Elias-Miroa, J.R. Espinosa, A. Pomarol


Certain surprising cancellations have been observed in calculation of RG running of higher-dimensional operators.  In some cases,  several Feynman diagrams contributing to the running cancel to ensure non-renormalization, without an apparent symmetry behind the cancellation. This paper explains the cancellation via supersymmetric non-renormalization theorems,  after embedding  non-supersymmetric theories into superspace.  



ANITA is launched!! (at least..)

by K. Mulrey


Katie Mulrey is this PhD girl in final-stage, working on the ANITA balloon project in the South Pole to measure Ultra High Energetic neutrino, at the typical GZK limit cut (around 10^19 eV). She is fun and write regularly in different review or blog the development of the ANITA project and the difficulties the team encounters days after days. This time, she described the (successful) first flight of the balloon after 5 previous unsuccessful attempts. This was on the 18th of December Zulu time, and you can see his way on the map, 36 kms of altitude!!  For an annotated version of the paper, just have a look there. We all hope ANITA will give us interesting results, as cosmic rays physics usually did in the history of particles physics.




3.55 keV line in Minimal Decaying Dark Matter scenarios

by  G. Arcadi L. Covi and F. Dradi


The phenomenology of some simple scenarios accounting for the recently claimed 3.55 X-ray signal is discussed. Here a fermionic (Majorana) Dark Matter candidate with mass of 7 KeV is coupled with standard model states through a scalar field charged (at least partially) under the standard model gauge group and capable of coupling also with only SM fermions. The X-ray signal is originated from a one-loop induced decay into a neutrino and a photon. The requirement of the correct Dark Matter lifetime and relic density, achieved by the freeze-in mechanims through the decay of the scalar fied in the Early Universe sets the prospect of detection at LHC of the scalar field. In this minimal setup the scalar field promptly decays, at the collider, into a quark and a lepton, in case carries color charge, or into a charged lepton and a neutrino, in case of only electroweak interactions. Two extensions are also discussed. In the first the DM decays into a photon and a new SM singlet, rather than a neutrino and the scalar field is coupled with top quarks, leading to top+missing energy signatures at LHC. This new scalar is very light and can be detected in CMB experiments through variations of N_eff. In the second the DM is also coupled to the Higgs and a neutrino and decay through W-loops. The scalar field features displaced decays in case its coupling with only SM fields are of the same order as the one with the DM.





Stabilizing the Higgs potential with a Z’

by S. Di Chiara, V. Keus and O. Lebedev


We all know that the recent «dada» of Oleg and others is to stabilize the Higgs up to the Planck scale (I still do not understand really why this obsession of the PLANCK scale, but why not.. Do you really think nothing is happening between?). We read already tons of paper, especially the ones of the Jose Ramon (Espinosa) team where they stabilized with a heavy singlet (that can also play the role of right-handed neutrino, see the work of H.M. Lee, J. R. Espinosa et al.). Very useful work and usually interesting results, as the ones we have in this article where Oleg et al. shows that not only a scalar, but a heavy Z’ can also play nicely the game. The paper would have been embedded in a GUT-like scenario, it would even have been better. The hurry guys can just jump on the Equation (19) and Figures 1-2, they will easily catch the main point and the result. PS. it is important to notice that this work is made by professional, so do not try to reproduce it at home.. ;-) In other words, a lot of computing/numerical subtelties are hiddeen in these 2-loops analysis, which make them not so easy to reproduce, even if the final result seems easy to understand. You can find an annotated version of the paper there.



Dark Matter 2014

by Marc Schumann


A veryyyyyyyy nice summary of the 2014 results, but more interesting of the 2015-2020 prospects in direct detection dark matter searches. Before everything, please notice the new arXiv numerotation 1501.01200, 5 digits precision, showing that if BICEP did not see hint of inflation, preprint productions for sure yes, welcome to the Physics 5.0 world!!! Concerning this paper, I let you read through, everyone can find his piece of cake to eat around. Those who want to understand better the principle or theory behind the direct detection can read the first sections and the nice Figure 2 to distinguish single phase/dual phase detectors. Those directly interested by a summary of the 2014 status have a look at Figure 1. I will present here the summary of the sensitivity for the next decade (all cross section given for a 50 GeV candidate): 

2014: LUX, 10^-45 cm^2

2015: DEAP3600 experiment, 10^-46 cm^2,

20017: XENON 1T, 2x10^47 cm^2

2018: LZ, 10^-48 cm^2 (just a factor of 5 above the neutrino wall).

So the next 3 years will be quite reach in fake signals. For an annotated version of the paper, run there.




Fermi/LAT observations of Dwarf Galaxies highly constrain a Dark Matter

Interpretation of Excess Positrons seen in AMS-02, HEAT, and PAMELA

by  A. Lopez, C. Savage, D. Spolyarz and D. Adams


Mmmmmmm. Let say someone had to do it. They lost at the game «courte paille», and so, they did it. Combining AMS and FERMI should be a numerical pain in the ass (I just suppose, I never did it), especially when you already know that the result will be negative and not impressive. They did it. good. So? Does not fit of course, incompatible, except for 4 muon channel. Which means you need to find a muonphylic dark matter which annihilate only into 4 muons. That is the real challenge....  For an annotated version of the paper, run there.