## Journal Club

Seminar Room, Mondays at 14:00

### Monday 14th of November, 2016

# Runaway Relaxion Monodromy

(Submitted on 17 Oct 2016)

We examine the relaxion mechanism in string theory. An essential feature is that an axion winds overN≫1 fundamental periods. In string theory realizations via axion monodromy, this winding number corresponds to a physical charge carried by branes or fluxes. We show that this monodromy charge backreacts on the compact space, ruining the structure of the relaxion action. In particular, the barriers generated by strong gauge dynamics have height∝e−N , so the relaxion does not stop when the Higgs acquires a vev. Backreaction of monodromy charge can therefore spoil the relaxion mechanism. We comment on the limitations of technical naturalness arguments in this context.

R. Vega-Morales

# Lattice QCD for Cosmology

(Submitted on 23 Jun 2016 (v1), last revised 27 Jun 2016 (this version, v2))

We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to several tens of MeV we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (chi) up to the few GeV temperature region. These two results, EoS and chi, can be used to predict the dark matter axion's mass in the post-inflation scenario and/or give the relationship between the axion's mass and the universal axionic angle, which acts as a initial condition of our universe.

Presented by A. Ayala