Wednesday, 27 May 2015

Planck 2015 Liveblog: Day Three Session Three

Today was the day of the conference excursion, to the Dodona archeological site/amphitheatre.  So we have only three sets of talks, finishing with the second set of parallel talks.  Thanks to the excursion, we're back on schedule, more or less, and I'm going to try changing sessions after three talks.

5:00 pm: "Supersymmetry and Naturalness", Csaba Balazs

Observable evidence of SUSY: got a job!

Why are we obsessed with SUSY?  Are we really obsessed with naturalness, and have just mistaken SUSY as the best example of that?

Naturalness is simply the statement that physics at different scales are well-separated.  To be quantitative, we must define a fine-tuning measure.  Use Barbieri-Ellis-Giudice measure for concreteness, to match with literature.  Important questions though; why is it a derivative?  What are we taking the derivative of (mZ, mH, v, ...)?  What are we taking the derivative with respect to (tan β, B, ...)?  Derivative or logarithmic derivative or ... ?

Bayesian motivation and answer for all these questions.  If e.g. theory predicts mZ (μ), this function is invertible: μ (mZ).  In Baysian analysis, using delta-function likelihood (since mZ well-measured) then evidence is just BEG measure.  This also makes it easy to generalise to multi-parameter theories (inputs and outputs), since replace derivative with Jacobean.

Result is that even CMSSM has ~few percent fine tuning regions.  CNMSSM is even better.  Extends up even to m0 ~ 10 TeV.

Why truncate plots at 16 TeV?  Limits of scan.  No fundamental reason.  Question remains how high this can go.
Regions of low fine tuning at EW scale fine tuned at high scales?  Likely.  Some degree of subjectivity in formalism.
Comment: frequentist interpretation: Jacobean is covariance matrix.
Low fine-tuning is focus point, small μ - yes.
Additional data would make fine tuning worse, remove these low-tuned regions - yes, upcoming work.

5:25 pm: "What is a Natural SUSY scenario?", Jesus Moreno

Ten minutes late already, which will make switching to the next session later trickier.

Naturalness given as caused by top loops.

Standard Lore is that stops should be light to have natural SUSY.  Also very light Higgsinos, not too heavy gluinos.  However, these are done in various approximations that are not robust.  We should not restrict ourselves to the leading-log approximation.  We also want limits in terms of physical masses, not Lagrangian parameters.

As known, focus point has heavy stops without paying much of a price in naturalness; Higgs runs insensitively to m0, while stop mass much more dependent.

Should also consider other fine tunings, e.g. that associated with large tan β.

Scan spectrum and express limits by computing BEG fine tuning.

I kind of lost interest in the second half of this talk.

6:10 pm: "Particle Cosmological Probes on Light Dark Matter", Kenji Kadota

I skipped a talk to get here on time.  Dark matter below DD range, with an electric dipole moment.  Constraints exist for LEP/LHC; consider extension to ILC and also supernovae.

ILC search based on clean mono-photon search.  Backgrounds (invisible Z, W) controllable.  SNe based on cooling constraints.  Collider gives upper bound of ~ 0.01 for dipole moment (in TeV-1),  Supernovae constraints exist at much lower moments, excluding between 10-5 and 10-6.

Also constraints from helioseismology.  Uncertainties not trivial, but easy to exceed them with DM so constraints can be made.

There's too much text on the slides that I literally cannot read, because it is too small.

I'm skipping the next talk, which is about inflation.

6:50 pm: "Hidden Sector DM in Non-Thermal Cosmologies", Bob Zheng

Ah, a talk on a paper I've read.  Aim was to classify possible non-thermal cosmologies in string/SUSY theories.  Generically get moduli, gravitationally coupled scalar fields that can lead to a period of pre-BBN matter domination.  (This gives lower bound on mass of 50 TeV.)  This significantly alters early-Universe cosmology.  Problems if moduli mass is at SUSY breaking mass.  Generically rule out standard neutralino.  So take some RPV, and let DM live in a hidden sector, where it is less constrained.

2-sector model with weak coupling.  This means that two sectors need not be in thermal equilibrium.  Classify models first by annihilation efficiency: is it larger than the Hubble rate when the moduli decays?  If so, DM insensitive to moduli decay (freezes out later, during radiation domination).  Otherwise things change somewhat.

For efficient annihilation, two subcases depending on whether DM is relativistic or not at reheating.  If so, standard freeze out.  If not, get additional production from moduli decay and final density tracks moduli density.

For inefficient annihilation, relic abundance gets two contributions: from moduli decay and from early-time freeze-out.

Indirect signals still possible if annihilation rate comparable to thermal WIMP.  This is because annihilate to light but unstable hidden sector states.  However, this implies an unbroken hidden-sector gauge theory.  (This is not ruled out if the hidden sector is colder than the SM, or the gauge group confines.)  This will affect structure formation.

Decays of non-LSPs?  Assumption that sectors weakly coupled means only LSP decays that way.
What about freeze-in?  Subsumed in the inefficient annihilation case.
Temperature of kinetic decoupling? Somewhat model-dependent.

7:10 pm: "Higgs Dark Matter from Warped Extra Dimensions", Aqeel Ahmed

Consider a Z2-symmetric RS (IR-UV-IR). This is to purely to give DM.  Bulk Higgs.  Got inert doublet model, somehow.

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