Monday, 23 May 2016

Planck 2016 Liveblog: Day One Session Two

Second session of the day looks quite technical.  Thankfully, at least for me, most other plenary sessions look more phenomenological.  We're running a few minutes behind already, thanks to the first session running about 15 minutes over.

11:30 am: Aspects of string phenomenology and new physics, Ignatios Antoniadis

People should really put their talks on the website before giving them.

Problem of scales: Dark Energy, Electroweak, Inflation and Planck.  Different scales implies hierarchy challenges.  Possible that some of these could be connected.  e.g. famous ADD large extra dimension theories, where true quantum gravity scale is close to EW scale.  Accelerator signals come at four different scales: gravitational radiation in the bulk (missing energy), string vibrations (dijet resonances), KK resonances, and extra U(1)s and anomaly induced terms.

D-branes used to generate gauge/fermion multiplets in the usual way.  Green-Schwarz mechanism: ALPs.  Generation of baryon/lepton number U(1)s automatically.

750 GeV resonance, spin-0/2 (but both closed string) explanation.  Related to anomaly cancellation; suppresses mass by order of magnitude from string scale.

Does string theory predict relative couplings to gluons/photons?  No.
Can explain 750 GeV using weak couplings to Planck scale if cross section is a bit smaller, say 3fb.
Strong CP problem? ...
How can 750 GeV explanation be checked?  String scale is not too large; LHC can not fully exclude, but 100 TeV can.

12:00 pm: Holographic renormalization group a la Wilson, Manuel Perez-Victoria

Holography: UV/IR conection.  e.g. AdS metric invariant under isometry x → tx, x → tz (scale invariance).  Theories around non-trivial solutions to gravity are dual to CFTs.  The duality interconnects RGEs to gravity EOMs.

Defining your terms is nice.

12:25 pm: Natural SUSY from x-dimensions, Mariano Quiros

Little hierarchy problem can be phrased as tendency for heavy stops to destabilize the EW vacuum.  Attempt to increase Higgs mass with either additional D- or F-terms.  D-terms require the Higgs to be charged under the new gauge group and imposes anomaly cancellation conditions.  F-terms do not require an extended gauge sector.  These correspond to adding a singlet (NMSSM) or triplet (TMSSM) to the theory.

Singlets are simpler, but tadpoles are a serious problem.  They generically destabilize any hierarchy.  This can only be forbidden by a symmetry, but then you have domain wall problems.  Triplets have tadpoles forbidden by gauge symmetry, but the challenge their is that EWPO constrain their VEVs to be small.

Go to 5D theory with Scherk-Schwarz breaking of SUSY.  Basic MSSM in flat 5D to start.  Bulk N = 2 SUSY broken to N = 1 by orbifolding, and all SUSY broken by twisted boundary conditions.  The Higgs soft masses are automatically such that they satisfy focus point conditions, i.e. the tree-level VEV is zero independent of the scale of the soft masses, and EWSB is purely radiative.  This is accomplished with bulk triplets and boundary-localised couplings to the Higgs.

Third generation sfermions boundary-localised.  Then only light sparticles, automatically natural spectrum.  DM is stau sneutrino (DD?).  DM is heavy (280 GeV) which leads to no collider stop bounds.  Indirect bounds from gluino searches bound to 550 GeV.

LSP DD question.  Indeed, can not be DM: must be unstable.
Stability of EW vacuum: not a problem now due to light stops, plus 1/R can be taken large.
Flavour physics: first two generations have aligned masses.

No comments:

Post a Comment