Journal Club
Seminar Room
If you want to propose a paper, you can contact Supratim Das Bakshi (sdb AT ugr.es)
Monday 15th of February, 2016
A Broadband Approach to Axion Dark Matter Detection
(Submitted on 2 Feb 2016)
When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axion dark matter with masses in the range of 10^{-13} eV to 10^{-6} eV, particularly the QCD axion with a GUT-scale decay constant.
Presented by R. Vega-Morales
Dark Sunshine: Detecting Dark Matter through Dark Photons from the Sun
(Submitted on 3 Feb 2016)
Dark matter may interact with the Standard Model through the kinetic mixing of dark photons,A′ , with Standard Model photons. Such dark matter will accumulate in the Sun and annihilate into dark photons. The dark photons may then leave the Sun and decay into pairs of charged Standard Model particles that can be detected by the Alpha Magnetic Spectrometer. The directionality of this "dark sunshine" is distinct from all astrophysical backgrounds, providing an opportunity for unambiguous dark matter discovery by AMS. We perform a complete analysis of this scenario including Sommerfeld enhancements of dark matter annihilation and the effect of the Sun's magnetic field on the signal, and we define a set of cuts to optimize the signal probability. With the three years of data already collected, AMS may discover dark matter with mass 1 TeV≲mX≲ 10 TeV, dark photon massesmA′∼(100) MeV, and kinetic mixing parameters10−11≲ε≲10−8 . The proposed search extends beyond existing beam dump and supernova bounds, and it is complementary to direct detection, probing the same region of parameter space for elastic dark matter, but potentially far more in the case of inelastic dark matter.
Presented by R. Vega-Morales
One-loop effective lagrangians after matching
(Submitted on 30 Jan 2016)
We discuss the shortcomings of the recently proposed functional method to compute the one-loop Standard Model (SM) effective lagrangian when the heavy fields couple linearly to the SM. In particular, one-loop contributions resulting from the exchange of both heavy and light fields must be explicitly taken into account through matching because the proposed functional approach alone does not account for them. We review a simple case with a heavy scalar singlet of charge−1 to illustrate the argument. As two other examples where this matching is needed and the functional method gives a vanishing result, up to renormalization of the heavy sector parameters, we re-evaluate the one-loop corrections to the T--parameter due to a heavy scalar triplet of hypercharge−1 coupling to the Brout-Englert-Higgs boson and to a heavy vector-like quark singlet of charged2/3 mixing with the top quark, respectively. In all cases we make use of a new code for matching fundamental and effective theories in models with arbitrary heavy field additions.
Presented by J. Santiago
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