Magic Monday Journal Club

18th November 2013

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Light Dark Matter Anomalies After LUX

by M. Gresham and K. Zurek

Haaaaa. Everyone was waiting for this paper (weird but the microscopic approach of Belanger et al. appeared before this work).

In this paper, Moira and Kathryn scan on many different possible effective operators trying to reconciliate DM «observations» to LUX/XENON results. Even playing with spin-dependent, momentum dependent, isospin violation, escape velocity, their analysis shows that «a light DM elastic scattering explanation for the DAMA, CoGENT and CDMS-Si anomalies appears to be substantially obstructed» (to stay politically correct, top of their page 13). For the hurry guys, just jump to the Equations (1-3) for the effective operators they used, (14-15) to have a feeling of the dependence on momentum/velocities and Fig.1 for the classical generic case, Fig.2 for the anapole/dipole interaction and Fig.3 for the isospin violating case. Then for the skeptical, their Fig.7 to see how conservative they tried to be concerning the Leff moto. What is still left to be done? Inelastic scattering, but I am pretty confident that I will have to present a paper about that in the following week(s).  You can find the annoted version of the paper here.

Exploring a Dark Sector Through the Higgs Portal at a Lepton Collider

by Z. Chacko, Y. Cui and S. Hong

In this work, the authors look at the prospect of contraining the invisible Higgs branching ratio for different kinds of benchmark linear collider scenario (from 250 GeV ILC to 350 GeV TLEP passing through 1 TeV ILC). Without wondering how realistic are this scenario, they found the the percent level could be reached, making this detection way more efficient that future direct detection prospect. Their results are summarized on Fig.6. However, be careful as for each range of the DM mass, a different type of linear collider scenario has been taken (look at the paragraph «combined result» to see the details) and even if it «seems» that for dark mater mass below 60 GeV (Higgs threshold for its decay) the ILC will be more efficient than XENON 1T, do not forget that they took in consideration a 1000 fb-1 / 250 GeV ILC which would not be avaible before 2030, at least 10 years after a XENON1T project. All in all, the analysis is quite nice to read. You can find an annoted version of the paper here.

Βounding the Higgs width at the LHC using full analytic results for gg -> 2e 2μ

by J.M. Campbell, R.K. Ellis, C. Williams

In this work, the authors revisit the hadronic production of the four-lepton final state, e^- e^+ \mu^- \mu^+, through the fusion of initial state gluons. This process is mediated by loops of quarks and they provide first full analytic results for helicity amplitudes that account for both the effects of the quark mass in the loop and off-shell vector bosons.They confirmed and extended a recent analysis of Caola and Melnikov that proposes to use a measurement of the off-shell region to constrain the total width of the Higgs boson. Using a simple cut-and-count method, existing LHC data should bound the width at the level of 25-45 times the Standard Model expectation.  In their analysis the bound on the Higgs width is improved by a factor of about 1.6 using a simple cut on the MEM discriminant, compared to an invariant mass cut m_{4l} > 300 GeV.

Probing Higgs couplings with high P_T Higgs production

by A. Azatov and A. Paul

In this work, the authors  study possible extensions of the Standard Model which predict modifications of the Higgs couplings to gluons and to the SM top quark. The values of these two couplings can, in general, be independent. They discuss a way to measure these interactions by studying the Higgs production at high p_T within an effective field theory formalism. They also propose an observable r_\pm with reduced theoretical errors and suggest its experimental interpretation.

Hidden Sector Dark Matter with Global U(1)X-symmetry and FERMI-LAT 130 GeV γ-ray Excess

by S. Baek and H. Okada

I would say that, generally speaking, writting an article about a 130 GeV line (which in fact is 135.. 133.. Anyway, around that value) is a little bit «cavalier» nowadays. But still some interesting ideas can emerge. I would not really consider this idea (based on the recent Weinberg model which aims was to fit an excess of cosmic neutrino) as especially seducive. The authors «fit» the FEMRI line through the annihlation of a dark matter charged into a U(1)X global group into 2 of its goldstone modes which in turn each of them decays into 2 pions and each pions decays into 2 photons (so 8 photons at the end of the process) thanks to the SM Higgs/Goldstone mixing. It thus justifies a 520 GeV DM candidate (130*4 for those who did not follow). The Goldstone mode should be around 500 MeV to respect the Weinberg condition on cosmic neutrino. No scan, no real analysis, just a sentence after Eq. (III.10) showing that for a reasonable set of parameters, conditions (intensity of the line + invisible Higgs decay constraints + LUX data) seem to be satisfied. Ok. Why not. I think this kind of paper will interest people interested in this kind of paper.  Jump on Fig.2 to understand the process and the conclusion for.. the conclusion. Their reference [7] is just a piece of diamond. You can find an annoted version of the paper here.

Reflections on the direct detection of particle dark matter

by R.H. Sanders

R.H. Sanders (a MOND afficionado) explains in this 4 pages why the «dark matter paradigm» is not a «scientific theory» because not falsifiable. Philisophical discussion, some interesting points cocnerning the sociology of Physics community (there is something «a la « Peter Woit in the Stirng field, same arguments used against the stringy guys). A little recreation for your metro transport.  You can find the annoted version of the paper here.

Planck’s law and the light quantum hypothesis

by S. Bose (1924)

In 1923 Bose submitted this paper to «Philosophical Magazine» which were the PRL of the time. It was rejected immediately. In despair, he wrote to Einstein and asked to him if he can translate it in german as he wrote «I do not know sufficient German to translate the paper» and submit it to «Zeitschrift fur Physik». In this paper, he rederivates the Planck formula without any pseudo-classical interpretation or motivation (Wien’s law..) but only  with pure quantum considerations. The article is incredibly modern and can be considered as the first quantum-thermodynamics paper. The help of Einstein can justify the name «Bose-Einstein statistics» to the last equation of the paper.  You can find the original paper here.