Friday, 29 May 2015

Planck 2015 Liveblog: Day Five, Session Two

The first of two parallel sessions, I'll be splitting my time between DM and SUSY.

12:45 pm: "Dark Matter: Connecting Direct Detection and LHC Searches", Andreas Crivellin

Loop effects very important here in EFT analysis.  Also consider MSSM with only SM Higgs/+ Heavy Higgs/+ Stops.

Key perspective is to use the equivalence of the DD and LHC couplings.

Crucially important ot include running, mixing and matching in EFT to properly relate experiments at different scales.  In particular, operators whcih do not contribute at tree level can give important loop corrections.  Examples include operators coupling to two gauge bosons, to heavy quarks, or vector-axial vector operators.

MSSM section is on a paper I read recently.  Interesting idea to add more and more sparticles to light spectrum (motivated by naturaleness).  Observe blind spots due to cancellations that are invisible to DD, but can be seen by combining LHC searches and flavour experiments such as b to sγ.

1:00 pm: "The Unnatural Composite Higgs", James Barnard

Theory can have as many tunings as predictions.  In particular, composite Higgses can have tunings both for Higgs VEV and mass (equivalently, μ2 and λ).  Aim is to properly quantify this.  Define vectors and hence surfaces for separate tunings.  If surfaces are aligned, tunings are dependent (only one).  If perpendicular, tunings are independent and get worse.

Then define matrix of inner products and take determinant to get tuning associated with multiple outputs.  Has sensible behaviour.

Apply to SO(5)/SO(4) models, with three possible choices for top embeddings.  Scan with MultiNest to be efficient.  Apply CMS top partner and LHC Higgs coupling bounds.  (5, 5) model is tuned due to fact Higgs mass comes from cancelling one-loop against two-loop term.  (14, 14) and (14, 1) models better, actually less tuned than naive estimates.

1:20 pm: "The Dark Side of Naturalness: Beyond the MSSM", Andreas Goudelis

Not a discussion of Higgs naturalness, but about DM constraints.

Though have used tuning for Higgsino mass...

Standard WIMP relic density (MSSM examples):
  • Adjust couplings, open/close annihilation channels (neutralino composition)
  • Mediator mass (light squark exchange, Higgs funnel)
  • Coannihilation (stau, stop, etc.) 
First has experimental constraints, latter two though are fine tuned.  Small variations of input parameters lead to large variations in relic density.

Consider extensions of MSSM with (Hu Hd)2 higher-dimensional operators.  These operators modifying the Higgs will necessarily also modify the Higgsino phenomenology.  To remain in EFT domain, need low to moderate tan β.  Also find new cancellations that allow "well-tempered" neutralinos, with comparable mixtures of Higgsino and Bino, to pass LUX constraints.  But these are still quite fine tuned.

Main benefit comes in with pure Higgsino DM.  Higgsino below W mass is fine with DD and relic density, but ruled out by LEP chargino search.  However, new effects can split the multiplet, allowing the neutral component to be light and the chargino to be heavy.  This seems to be the only natural neutralino DM remaining in the MSSM.

What if only impose bound of not overclosing universe?  Things get better, see plenary talk from yesterday.

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