Wednesday, 27 May 2015

Plank 2015 Liveblog: Day Two Session Four

The final session of the day is the first parallel session of the conference.  According to the conference timetable, the first talk was supposed to be at 5pm.  Even if we hadn't been running late, that would have left us with no time for the coffee break; or to put it another way, the schedule had an error.  Which isn't exactly a surprise for thie conference.  As it is, it looks like this session will start at 5:40pm, and so probably not finish till 8.

Given how bad timekeeping has been at this conference, I'll mostly stay in this session.  There is one talk at the end of another session I want to attend, though.

"Dark Matter with Ultra Compact Mini Halos", Ki-Young Choi

Consider a non-standard cosmology with an early matter-dominated era; e.g. with early curvatons or other moduli.  How to probe this?  Perturbations grow linearly in this time, compared to logarithmically during radiation domination.

Usually suppress structure by kinetic decoupling scales; not true in matter domination.  Kinetic decoupling usually occurs at 5 - 1000 MeV.  Sets smallest proto-halos.  Compare free-streaming length, which also smooths out small scale structure.

Is DM populated by scalar decay?  Assumed thermal.
When does matter domination occur?  Must be close to BBN to give observable features.

"Modulation, Asymmetry and the Diurnal Variation in Axionic Dark Matter Searches", J Vergados

A lot of review here.

Okay, finally actually getting to axions.

Slide filled with textextextextextextextext

Axion is cold, so same velocity profile.  (One?) detection channel is conversion to photons in magnetic field (Primakoff effect).

Here's some stuff.  And here's some more stuff.  And this is also stuff.  Equations!

"Simplified SIMPs at the LHC", Bryan Zaldivar

Self-interactions motivated by astro small-scale problems (too big to fail, etc).  Many constraints when DM interacts strongly with SM.  Need repulsive potential (heavy water), asymmetric or non-thermal (relic density), and fermionic (neutron star collapse).

LHC signature is trackless jet.  Neutron-like signal and no MET; neutral and strongly interacts with detector.  QCD background is huge.  Use number of tracks and charged energy fraction as discriminants.  Claiming a pretty good discrimination, though I'm a bit skeptical.

"Asymmetric Self-interacting Dark Matter", Kallia Petraki

Standard arguments for asymmetry, self-interactions.  Large self-interactions points to light force mediator.  Also gives desired velocity dependence of scattering; larger in smaller objects (dwarf spheroidals).  Large couplings to light mediator another reason to want asymmetric DM; efficient annihilations of DM to mediator.

DM of this kind typically forms bound states.  This rich spectrum then has many implications for observables.  Minimal idea is "atomic DM": force is dark QED.  DM must be multi-component, i.e. "electron" and "proton".  Need to break dark force giving light vector.

Cosmic history: asymmetry must be generated before dark freeze out.  After annihilating away symmetric component, recombination (form dark atoms).  Dark photon phase transition must happen after this.  Massive dark photon then offers a path for indirect detection through kinetic mixing (decay to SM).  Direction to explain INTEGRAL 511 keV line.

Dark atoms produced in Supernovae?  No, they are hydrogen-like.
Challenge to asymmetric argument.  Also, question about generation of asymmetries.  Not a focus of this talk; many models exist, assume one can work.
Kinetic mixing leading to millicharges?  Dark photon has mass.
How is dark U(1) broken?  Dark Higgs.  Brought up that can do with Stuckelberg.

"Dark Matter and Gauge Coupling Unification in Non-supersymmetric SO(10) Grand Unified Models", Natsumi Nagata

Dark matter is traditionally stabilised by a discrete symmetry.  If this is just added by hand, this is less than ideal.  Can we do better, outside of SUSY or UED?  Simple as a remnant of e.g. a U(1) symmetry broken by a Higgs.  This is naturally contained in SO(10), which breaks to SU(5) x U(1).  Remember that this GUT can work outside of SUSY.

If Higgs is 126 (672, ...) residual symmetry is Z2 (Z3, ...).  Systematically construct both thermal and non-thermal models.  Come up with a new name for non-thermal models, because that's highly necessary.  Non-thermal models here produced through heavy (but not GUT-scale) intermediates, freeze in?  Intermediates exitst for unification.  Must reheat below their mass scale.

2 Candidate models constructed.  Proton lifetime within reach of future experiments.

"Non-custodial Warped Extra Dimensions at the LHC", Barry Dillon

For the last talk of the session I've decamped to something more towards collider pheno.  Addressing S and T parameters.  Consider a bulk Higgs to reduce corrections.  Still gives KK scale above 8 TeV.  Too high to be observable at LHC.  Can reduce problems using custodial SU(2) (or other ideas, e.g. deformed geometry).

Trying to solve problem using higher-dimensional operators.  Effect is not so much a cancellation of leading order term with these operators, as changing the relationship between S and T to lie closer to the long axis of the preferred ellipse.

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