## Journal Club

Seminar Room

### Thursday 1st of February, 2018

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

(Submitted on 26 Apr 2017)

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 decaysh→Za andh→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 decaya→γγ , even if the relevant couplings are loop suppressed and thea→γγ branching ratio is less than~1.

Presented by Roberto VM

# New LHC bound on low-mass diphoton resonances

(Submitted on 4 Oct 2017 (v1), last revised 27 Nov 2017 (this version, v2))

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.

Presented by Roberto VM

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

(Submitted on 30 Oct 2017)

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 of1011 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.

Presented by Mar B

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

(Submitted on 18 Dec 2017)

The CP asymmetry inτ→KSπντ , as measured by the BaBar collaboration, differs from the Standard Model prediction by2.8σ . 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 andD -D¯ mixing. These observations together imply that it is extremely difficult to explain the currentτ→KSπντ measurement in terms of physics beyond the Standard Model originating in the ultraviolet.

Presented by Jose S

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