Wednesday, 22 May 2013

Planck 2013 Day Three Live Blog 4

Last parallel session of the day, and I'm going to the Dark Matter session.  Conference Website.

4:00pm: Tiziana Scarna, "Effective Theory of Dark Matter Decay into Monochromatic Photons and its Implications: Constraints from Associated Cosmic-Ray Emission"

That's not a title, that's an abstract.  No surprise the title on the slide is shorter.

Decaying dark matter might be able to produce more gamma rays than annihilation; why?  Total annihilation cross section is fixed by relic abundance, and then expect photons to be loop suppressed; no such factor for decays.

If DM decays to the SM, it must have a lifetime in excess of 1026 seconds.  A dimension 6 operator with a GUT scale suppression would give the right suppression (for EW-scale DM).  So construct all operators that can contribute (with at most one non-DM BSM particle).  About 30 such operators, as photon can only couple through field strength tensor (neutral).

Three dimension five operators, two each for scalar, fermion and vector DM.  Larger but still manageable at dimension six.  All operators can also lead to at least decays to Z bosons, which will contribute to cosmic ray signals.  Those can be used to place constraints.

Constraints based on diffuse photon and antiproton observations.  The former dominate at high mass, the latter at low.

4:20pm: Stefan Vogl, "Internal Bremsstrahlung Signatures from Dark Matter Annihilations in Light of Direct Detection and Collider Searches"

Internal bremsstrahlung is possible source of hard photon from three body final state.  Most interesting in cases where the two-body final state without the photon is chirality suppressed, such as a Majorana fermion DM particle.  The three-body state with the photon is not suppressed, which off-sets the phase-space suppression.

IB can fit 130 GeV; not shown how this compares to a line.

Use other observations to constrain this possibility.  What observables are predicted?  Always have other SM fields, so always other photons.  Specific toy model in question has Yukawa-like couplings to quarks, so direct detection constraints; while intermediary scalar must be coloured and couples to gluons.

4:40pm: Camilo A Garcia Cely, "Study of internal bremsstrahlung in the inert doublet model"

Three exclamation marks.  Oh dear.

Splitting of inert doublet is set by Higgs VEV; so easy to go to limit where splitting is small compared to mass, and this is the limit where IB becomes important.  This puts the DM in the TeV range, so it annihilates to Higgses and gauge bosons.

The inert doublet model in this domain is very bad for the two-photon final state, because the rates to W/Z are so large.  That makes IB an attractive possibility.  The existence of t-channel annihilation through the charged scalar makes IB more important than FSR.  This is not due to chiral suppression, but a purely phase space effect when the charged scalar is nearly degenerate with the DM.

As yet, this is unconstrained by HESS.  However, the limits are only one to two orders magnitude too weak.

5:00pm: Yi Cai: "Dark Matter and Co-annihilation"

Yet another effective operator approach.  Not that there's anything wrong with that.

Recall the previous work, where we relate operators with direct detection and collider searches; as is well known, the collider searches win comfortably at low masses.  However, there are concerns about the collider limits; in particular, perturbativity and the need for a UV completion.  Relic abundance is also a potential problem.

Coannihilation is an alternative mechanism to get the correct relic abundance in a thermal process.  Our effective theory of the dark sector now contains two particles; direct detection is not usefully constrained, but collider constraints are still relevant.

Not trivial to fit the relic abundance in the effective theory, but I didn't follow why.  It doesn't help that the plots are too small to read.

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