Magic Monday Journal Club

27th November 2013

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Higgs to tau tau : CERN seminar ATLAS

by ATLAS collaboration

Yesterday ATLAS  presented  new results of the Higgs search in the tau-tau decay channels using the full dataset at 8 TeV.  The measured rate  is mu = 1.4+0.5-0.4, in agreement with the SM, and the signal hypothesis is favored at the 4.1 sigma level over the background-only hypothesis.  This is the first direct evidence for Higgs decays to fermions  (although more than 3 sigma evidence could previously be obtained indirectly, from global fits to the Higgs couplings by combining the ATLAS and CMS data),  and a strong hint that the Higgs field is responsible not only for the W and Z mass but also for the fermion mass generation. 

Constraining Non-thermal and Thermal properties of Dark Matter

by P.S. Dev, A. Mazumdar and S. Qutub

In this work, Mazumdar and friends look at different scenarii of dark matter genesis. From freeze out to freeze in passing to non-thermal production. They integrate the Boltzmann equation from reheating temperature given by inflaton decay to the nowadays temperature. A project I was working on in fact (but I wil survive, thanks for the support). The article is easy to read, good for an evening metro trip back home. If you are in a hurry, jus tlook at Eq.(2.5) and (2.6) for a reminder of Boltzmann equations and solution. Chapter 3 is classical, nothing new, except equation (3.12) where you have the freeze in solution including the primordial density at reaheating temperature produced by inflaton decay. The part 3.2 is the same with a null annihilation cross section (all the DM is created by the inflaton decay). A look at (the horrible) Fig. 1 help to understand the mechanism  whereas Fig. 2 shows quite nicely the parameter space allowed depending on the reheating temperature. For the rest of the paper, the authors wanted to combined all the constraints (indirect FERMI, HESS, BBN...) . The only interesting points on the Figs. 3-6 is the influence on the overclosing Universe: even small cross section can keep the universe quite open due to its non-thermal component released by the inflaton decay. Same for the Fg.7 in pure non-thermal case.   You can find an annoted version of the paper here.

Determine the mass of invisible particles: Application to the Higgs invisible decay

by J. Wang

In this paper, Jian propose two observables (R1 and R2, see equations 6 and 7) which should be able to distinguish if a pT missing is coming from an invisible Z, invisible Higgs or effective operators of the types Eq.(2). Its conclusion is quite clear : yes! as you can clearly see on its figure 5. the analysis is simple but seems reasonable. The only «critics» would be the choice of the operators (2) [why these ones?], but as he argues, it is an example to apply his selection proposal. So let’s do it.   You can find an annoted version of the paper here.

Global Constraints on Lepton-Quark Contact Interactions

by J. de Blas, M. Chala, J. Santiago

Mikael (dit «Miki») from Granada came  to friendly visit us to present his last work. where they present a simple yet general parameterization of the effect of an arbitrary number of lepton-quark contact interactions on any di-lepton observable at hadron colliders. This allows them to bound arbitrary regions in the parameter space of these operators, using not only LHC data, but also  EWPD for comparison. They assume that the scale of new physics is well beyond the reach of LHC (and common to all the operators involved in the effective lagrangian) and that the relevant degrees of freedom and symmetries are those of the Standard Model. For the hurry guys, the main result is given by the master formula in equations (4), (5) and Table  I.

Update on Light WIMP Limits: LUX, lite and Light

by E. Del Nobile, G. Gelmini, P. Gondolo and J-H. Huh

The real question about this work, which is obviously solid, (relatively) clear with trustable results, is : isn’t it too late? I would say that you will recover mainly the results obtained by Zurek et al. (we discussed this article the preceeding week) but less complete concerning the model studied. Only the isopsin violation model is studied here. The statistical analysis is stronger and more conservative, even than the LUX experiment itself (the authors use the statistical Maximal Gap method). However, their main conclusion is almost similar to the one of Zurek et al except in some small regions of parameter space. So jump directly to the figure 2 and compare to the Zurek paper. You can find an annoted version of the paper here.

Hidden Enhancement of Majorana Dark Matter Annihilation Through Higgs Bremsstrahlung

by F. Luo and T. You

I did not know the works of these authors before. They applied the famous internal bremsstrahlung effect (increasing the annihilation cross section because the three bodies final state is not helicity suppressed) to a SM Higgs boson in the final state. You will find the Feynman diagrams of the processes involved in figure 1 (just the 2 with internal Higgs produced are not null in the case of nul fermionic mass in the final state). The toy model they took in their equations (2.1) and (2.2) is not really interesting nor justified, but this kind of effect can be present in SUSY models for instance. Figure 2 shows the importance of the Higgs strahlung and the total cross section with and without the Higgs final state is shown in Fig.7. I am quite surprised of the magnitude of the effect and I would be curious to see it in a more motivated model like SUSY for instance. You can find an annoted version of the paper here.

An explicit Z’-boson explanation of the B -> K*mu+mu- anomaly

by R. Gauld, F. Goertz, U. Haisch

Florian was came from Zurich in our journal club and gave us a very nice «mini-seminar» on  his recent work. Great presentation FLorian masterize the field and it is a pleasure to discuss the subject with him. Motivated by the anomaly recently discovered in the decay B->K*mu+mu-, a model independent triple-correlation between new physics in B->K*mu+mu-, B_s-Bbar_s mixing, and non-unitarity of the quark-mixing matrix has been presented in the framework of minimal Z' setups (1308.1959). It has been demonstrated how this correlation can be used to test the explanation of the anomaly via a large negative contribution to the semileptonic vector operator by measurements of DeltaM_{B_s} and of Vud, Vus, Vub.  In 1310.1082 an explicit model of 3-3-1 type was presented that just generates the sought pattern of new physics to address the anomaly. A variety of flavor, precision and collider observables have been analyzed and it has been shown that the model so far evades potential exclusions from other observables. Future prospects for seeing further signatures of the model have been discussed.

Higgs Production in General 5D Warped Models

by M. Franck, N. Pourtolami, M. Toharia

Adrian Carmona came also from Zurich to visit us and took the opportunity to present us this cool paper where the authors compute the production rate of the Higgs boson at the LHC in the context of 5D warped scenarios with a modification of conformality near the IR brane, an interesting alternative to custodial setups.

The Vortex Atom

by W. Thomson (Lord Kelvin)


Watching his colleague Tait smoking cigarettes, and observing the rings produced, Lord Kelvin have a look at the article of Helmotz published some years ago about Vortex in perfect fluid. Helmotz concluded his article by the fact that a vortex is stable and cannot be destroy if the fluid is perfect. With the existence of aether as a perfect fluid, and taking into account the elascitcity of the ring, the vortex was a perfect candidtate for the atom. Lord Kelvin added discrete vibration modes (first quantization) around the ring, explaining the double ray of sodium. Where does the roing come from? «act of creativity» he claimed («god» in other language). Not an article so easy to read, but clearly, the first string article. But only closed quantum string (in 1867!!).