Journal Club

Seminar Room

Thursday 1st of February, 2018

Hour: 10:00

Title: A Cosmological Signature of the Standard Model Higgs Vacuum Instability: Primordial Black Holes as Dark Matter

Presented by: Mar Bastero Gil

Ref: https://arxiv.org/abs/1710.11196v1

Abstract:

For the current central values of the Higgs and top masses, the Standard Model Higgs potential develops an instability at a scale of the order of 1011 GeV. We show that a cosmological signature of such instability could be dark matter in the form of primordial black holes seeded by Higgs fluctuations during inflation. The existence of dark matter might not require physics beyond the Standard Model.

Hour: 10:00

Title: A no-go theorem for non-standard explanations of the τ→KSπντ CP asymmetry

Presented by: José Santiago Pérez

Ref: https://arxiv.org/abs/1712.06595v1

Abstract:

The CP asymmetry in τ→KSπντ, as measured by the BaBar collaboration, differs from the Standard Model prediction by 2.8σ. Most non-standard interactions do not allow for the required strong phase needed to produce a non-vanishing CP asymmetry, leaving only new tensor interactions as a possible mechanism. We demonstrate that, contrary to previous assumptions in the literature, the crucial interference between vector and tensor phases is suppressed by at least two orders of magnitude due to Watson's final-state-interaction theorem. Furthermore, we find that the strength of the relevant CP-violating tensor interaction is strongly constrained by bounds from the neutron electric dipole moment and D-D¯ mixing. These observations together imply that it is extremely difficult to explain the current τ→KSπντ measurement in terms of physics beyond the Standard Model originating in the ultraviolet

Hour: 10:00

Title: LHC as an Axion Factory: Probing an Axion Explanation for (g-2) with Exotic Higgs Decays

Presented by: Roberto Vega-Morales

Ref: https://arxiv.org/abs/1704.08207v1

Abstract:

We argue that a large region of so far unconstrained parameter space for axion-like particles (ALPs), where their couplings to the Standard Model are of order (0.01−1)TeV−1, can be explored by searches for the exotic Higgs decays h→Za and h→aa in Run-2 of the LHC. Almost the complete region in which ALPs can explain the anomalous magnetic moment of the muon can be probed by searches for these decays with subsequent decay a→γγ, even if the relevant couplings are loop suppressed and the a→γγ branching ratio is less than~1.

Hour: 10:00

Title: New LHC bound on low-mass diphoton resonances

Presented by: Roberto Vega-Morales

Ref: https://arxiv.org/abs/1710.01743v2

Abstract:

We derive a new bound on diphoton resonances using inclusive diphoton cross section measurements at the LHC, in the so-far poorly constrained mass range between the Upsilon and the SM Higgs. This bound sets the current best limit on axion-like particles that couple to gluons and photons, for masses between 10 and 65 GeV. We also estimate indicative sensitivities of a dedicated diphoton LHC search in the same mass region, at 7, 8 and 14 TeV. As a byproduct of our analysis, we comment on the axion-like particle interpretation of the CMS excesses in low-mass dijet and diphoton searches.