Magic Monday Journal Club

6th January 2014

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Before everything, all the Magicians of the MMJC want to wish you a great new years 2014 full of joy, peace, articles, and  ideas. This journal club was the epiphany journal club, and our Magic king was Emilian Dudas and queen Jeremie Quevillon who deserve their crown. Congratulation to them!!!







A New Indirect Probe of the Higgs Self-Coupling

by M. Mc Cullough


The paper points out the sensitivity of the Z + Higgs production process in e+e- colliders to the  value of the cubic Higgs couplings.

Deviations of the latter at the level of 30% from the Standard Model value could lead to a measurable (0.5%) deviation of the cross section.  An interesting fact that apparently has not been pointed out before.




Dark Invisible Z’ and Dark Matter :LHC vs LUX constraint

by G. Arcadi, Y. Mambrini, M. Tytgat and B. Zaldivar


Ok, ok ok... Is it really fair that I present on of my article. Not sure about the fairness of the procedure, but at least, I think I know a little bit about it. In this work, we combine the LUX and LHC constraint on a generic model of dark matter (described just by its mass and V-A gamma5 coupling) to show that the LUX restriction on its invisible width is such that it should have been discovered at LHC in the dilepton channel, unless its mass is above 2.5 GeV. This can be apply to any Z’ motivated construction (SSM, E6, B-L...) and exclude strongly the plane (Dark matter mass; Z’ mass) as you can see on the figure 7. The only way to really avoid this strong constraint is to suppose a coupling almost exclusively axial, far from being natural in classical extensions of the Standard Model. For the hurry guys, jump on the equations 8 and 10 and the figures 5 and 7 which summarize very well the results (after a look at Eq. 1 to nderstand the notations).   You can find an annoted version of the paper here.




Electric discharge in vacuum by minicharged particles

by X. Li  and M.B. Voloshin


Mmmmmm.. So first of all, before reading the paper, I propose you to jump directly to the list of references. I think it is the older list I never read (except for the historical articles of course!!). There are 21 citations, so I decided to make the mean years of the citations (really nothing to do during weekends, yes..):  1979.24, with the first reference from 1925. Not so bad! In this work, the authors show that if a very light charged particle exist (below 10^-4 eV), a charged sphere of 1cm under 100kV can be discharged before 100 days by the creation of particle-antiparticle pairs even if the light particles created have a minicharge below 10^-8 units of electromagnetic charge. This value is largely comparable to limits existing and the experiment quite easy to build: a charged sphere of 1cm under a tension of 100kV is sufficient. For the guys who just have one metro stationn before his home sweet home, he can read directly the equation (2) and its integration on space, Eq.(7) which gives at the end the expression (1) which is much more than explicit. The limit of validity  [coming from the tunneling effect induced by the Nikishov-induced formula (2)] is given by expression (4): the higher is the mass, the stronger the tunneling suppresion is and the pair creation is then too weak to discharge the sphere.  You can find an annoted version of the paper here.




Is There a Hidden Principle in the Higgs Boson Decay to Photon

by A. Alves, E. Barreto, A.G. Dias


So, I notice that Brazilians not only prepare the worldcup this year but also work on Higgs to gamma gamma measurements. To sum up their idea comes from the remark that a 125.66 GeV Higgs is very close from the Higgs mass maximizing the gamma gamma branching ratio (126.2 or 125.5 GeV depending the the set of SM parameters used, see their table I), they upgrade this observation to a «principle». It means, if you suppose that a model  exist where by «principle» the Higgs to gamma gamma ratio should be maximal, they deduce that the SM should be.. the SM. In other words, if one had 2 families or 4 colors, the branching ratio to gamma gamma would be maximized for another Higs mass (for instance 100 GeV for 2 families, see their Figure 3). From the same idea, they also «predict» the W mass as for another mass, the changing in H-> WW width, will displced the maximum (see their Figure 2). All in all, a quite nice paper to read. Not sure they convinced me about this «principle» as they do not motivate it, but who knows... You can find an annoted version of the paper here.




The Price of a Dark Matter Annihilation Interpretation of AMS-02 data

by V. Spanos


Vassilis is a regular collaborator of J. ellis and K. Olive. When I first read the title, I thought «why Vassilis is coming after the war finished?». In fact, there was still some fighters to kill, he killed them. He took a simple theoretical constraint that was underestimate in the preceeding studies : the unitary limit, mixed with the last FERMI/HESS data and obtained his nice Figure 7 that you can copy and paste for your next Dark Matter local summary seminar you wil be asked to give. An excess in hadronic of gaugonic channel is excluded by unitary constraint, whereas if the excess of positrons is  produced by a mu mu or tau tau annihilation  final state, it is now excluded by the last dSph data of FERMI. At least, it closes the AMS/PAMELA chapter. You can find an annoted version of the paper here. Reading the underlined parts will be sufficient to understand its main results.




Higgs from the top

by  T. Han, R. Ruiz


Kinematically, top quark can decay to the Higgs boson, but the branching fraction is very small in the Standard Model. The leading decay channel is t \to h W* b, with the branching fraction of order 10^-9, which is not observable in a foreseeable future.  The paper considers  whether this decay channel can be enhanced by new physics, for example in 2-Higgs-doublet models or in the presence of higher-dimensional operators.  The conclusion is  rather negative: the enhancement by a factor of a few is possible, but that is not enough to make this decay observable.





What if you walk toward a star at a fixed speed?

by N. Murdoch


The author considers possible trajectories of the 3 kings as they follow a star or a planet.




On the elementary electrical charge and the Avogadro constant

by R. Millikan

1913


Robert Millikan was working in Chicago when he made this measurement of the elementary charge. Thomson and Townsend in Cambridge were already working on the subkject too, with the similar aparatus and idea: measuring the fundamental electric charge from the equilibrium between gravity and electric field for a drop of liquid. However, Thomson and Townsend were using water or alcohol, which evaporates very quickly, and their measurements was at least a factor 4 below the real one. Millikan changed the liquid to be oil, much more stable, and obtained a value of the charge, at 0.2% precision with the one we measure now!!! The ratio m/e being already calculated by Thomson, Millikan could then deduce the absolute mass of the electron. You can find an annoted version of the paper here. For more detailed precision and the annoted version of the paper, you can go to the book section where I go into historical details in the book «Le siècle des révolution». You can also find the preceding artcile of Millikan (1911) in the historical section where the method is also discussed, but this paper was very controversial concerning his results.





ARTICLE OF THE WEEK!!