Invisible's Journal Club
Past events
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Date of the event: Tue, 09/06/2015 - 15:00
Date: June 9th 15 PM (CET)
Presenter: M. Laine (Bern U)
Title: Gravitational wave background from Standard Model physics
Abstract: Apart from CMB photons and neutrinos, another principal carrier of information from very early epochs in the history of the universe are gravitational waves. Besides inflation, they have been proposed to contain features originating from post-inflationary phenomena such as preheating or thermal phase transitions. However, a gravitational wave background, akin to blackbody radiation, is also being emitted from a plasma without any phase transition. In this talk the general properties of the thermal background are discussed. The absence of additional relativistic degrees of freedom in Planck data sets an upper bound on the total energy density carried by gravitational waves and thereby on the highest temperature of the radiation epoch. Theoretically it might even be possible to observe the thermal background with future generations of GHz range detectors.
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Date of the event: Tue, 26/05/2015 - 15:00Date: May 26th 15 PM (CET)Presenter: C. Hill (Fermilab)Title: Axion Induced Oscillating Electric DipolesAbstract: An oscillating cosmic axion dark matter field will induce an oscillating electric dipole for any magnetic dipole. This may offer a new detection venue for the axion.
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Date of the event: Tue, 28/04/2015 - 15:00Date: April 28th 15pm CETPresenter: R. Sundrum (Maryland U)Title: Naturalness in the Dark at the Large Hadron ColliderAbstract: "Top partners" (such as the SUSY stop) are essential components of most mechanisms for solving the electroweak hierarchy problem, and therefore a central target of LHC searches. I will point out the loophole in arguments suggesting such partners should always be colored (and therefore easily produced). I then review the Twin Higgs mechanism for solving the little hierarchy problem with a dark (standard model neutral) sector, including an uncolored top partner, coupled to the standard model via the Higgs portal. After developing the minimal bottom-up model of this type I will describe its novel phenomenology in terms of displaced vertex decays of the Higgs boson.
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Date of the event: Tue, 21/04/2015 - 15:00Date: April 21st @ 15:00 pm (CET)Presenter: T. J. Weiler (Vanderbilt U)Title: Dark Matter at the LHC: EFTs and gauge invarianceAbstract: Effective field theory (EFT) formulations of dark matter interactions have proven to be a con- venient and popular way to quantify LHC bounds on dark matter. However, some of the non- renormalizable EFT operators considered do not respect the gauge symmetries of the Standard Model. We carefully discuss under what circumstances such operators can arise, and outline poten- tial issues in their interpretation and application
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Date of the event: Tue, 24/03/2015 - 15:00
Date: March 24th @ 15:00 (CET)
Presenter: M. Lisanti (Princeton U)
Title: Bringing Dark Matter into Focus
Abstract: Although dark matter comprises the vast majority of the matter in the universe, its properties remain elusive. Direct detection experiments are a promising avenue for discovering and characterizing the dark sector. These experiments seek toidentify dark matter particles as they scatter off nuclei in underground detectors.The standard picture since the 1980s is that the scattering rate modulates annually due to the Earth's orbit around the Sun. We have recently discovered a new modulation effect: Unbound dark-matter particles are focused by the Sun's gravitational potential, affecting their phase-space density in the lab frame. This 'gravitational focusing' results in a significant overall shift in the phase of the annual modulation and provides a powerful new tool for characterizing the properties of the dark matter particle. Gravitational focusing has additional applications to relic neutrino searches, providing the only source of annual modulation in that case.
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Date of the event: Tue, 24/02/2015 - 15:00
Date: February 24th @ 15:00 (CET)
Presenter: Andrea Wulzer (Padova U.)
Title: Robust collider limits on heavy-mediator dark matter
Abstract: We explain how to consistently use Effective Field Theories (EFTs) to set universal bounds on heavy-mediator Dark Matter at colliders, without prejudice on the model underlying a given effective interaction. We illustrate the method for a Majorana fermion, universally coupled to the Standard Model quarks via a dimension-6 axial-axial four-fermion operator. We recast the ATLAS mono-jet analysis and show that a considerable fraction of the parameter space, seemingly excluded by a na\"ive EFT interpretation, is actually still unexplored. Consistently set EFT limits can be reinterpreted in any specific underlying model. We provide two explicit examples for the chosen operator and compare the reach of our model-independent method with that obtainable by dedicated analyses.
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Date of the event: Tue, 10/02/2015 - 15:00Date: February 10th @ 15:00 (CET)Title: Higgs inflation as a miragePresenter: J. Barbón (IFT-UAM)Abstract: Models of Higgs inflation are constructed by a naive UV extrapolation of a very particular effective action. This procedure clashes with standard notions of effective field theory. In particular, the extrapolation must be trusted over a large hierarchy of intermediate scales. We introduce a simple toy model as a partial UV completion, in which this intermediate hierarchy is generated by a tuning of relevant operators in the UV theory. We further discuss how this model can be used to quantify the accuracy of the extrapolation procedure (or rather the lack of it).
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Date of the event: Tue, 27/01/2015 - 15:00Date: January 27th @ 15PM (CET)Title: Neutrino masses from cosmological intergalactic dataPresenter: Matteo Viel (Trieste Observatory)Abstract: I will review the tightest constraints that can be obtain from the Lyman-alpha forest on: neutrino masses and cold dark matter coldness. I will also discuss consistency with other data sets (CMB, weak lensing and cluster number counts). Finally I will present the forecasts on the above quantities that could be obtained with future observations.
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