Flavoured warped axion

We consider a 5D extension of the DFSZ axion model that addresses both the axion quality and fermion mass hierarchy problems, and predicts flavour-dependent, off-diagonal axion-fermion couplings. The axion is part of a 5D complex scalar field charged under a U(1)PQ symmetry that is spontaneously broken in the bulk, and is insensitive to explicit PQ breaking on the UV boundary. Bulk Standard Model fermions interact with two Higgs doublets that can be localized on the UV boundary or propagate in the bulk to explain the fermion masses and mixings. When the Higgs doublets are localized on the UV boundary, they induce flavour diagonal couplings between the fermions and the axion. However, when the Higgs doublets propagate in the bulk, the overlap of the axion and fermion profiles generates flavour off-diagonal couplings. The effective scale of these off-diagonal couplings in both the quark and lepton sectors can be as small as 1011 GeV, and therefore will be probed in future precision flavour experiments.

Scale and quality of Peccei-Quinn symmetry and weak gravity conjectures

The promising solution to the strong CP problem by a Peccei-Quinn (PQ) symmetry may introduce quality and hierarchy problems, which are both relevant to Planck physics. In this paper, we study whether both problems can be explained by introducing a simple hidden gauge group which satisfies the WGC or its variant. As a concrete example, we point out that a weakly-coupled hidden SU(N ) gauge symmetry, which is broken down to SO(N ), can do this job in the context of a Tower/sub-Lattice WGC. Cosmology is discussed.

Scalar dark matter probes the scale of nonlocality

Scalar dark matter (DM) in a theory introduces hierarchy problems, and suffers from the inability to predict the preferred mass range for the DM. In a WIMP-like minimal scalar DM setup we show that the infinite derivative theory can predict the DM mass and its coupling. The scale of nonlocality [Formula: see text] in such a theory in its lowermost limit (constrained by LHC) implies a DM mass [Formula: see text] TeV and a coupling with the Standard Model (SM) Higgs [Formula: see text]. Planned DM direct detection experiments reaching such sensitivity in the DM will effectively translate into lower bounds on the scale at which the nonlocality comes into the play.

The Importance of Scalar Fields as Extradimensional Metric Components in Kaluza-Klein Models

Extradimensional models are achieving their highest popularity nowadays, among other reasons, because they can plausible explain some standard cosmology issues, such as the cosmological constant and hierarchy problems. In extradimensional models, we can infer that the four-dimensional matter rises as a geometric manifestation of the extra coordinate. In this way, although we still cannot see the extra dimension, we can relate it to physical quantities that are able to exert such a mechanism of matter induction in the observable universe. In this work we propose that scalar fields are those physical quantities. The models here presented are purely geometrical no matter the fact that Lagrangian is assumed and even the scalar fields are contained in the extradimensional metric. The results are capable of describing different observable cosmic features and yield an alternative to ultimately understand the extra dimension and the mechanism in which it is responsible for the creation of matter in the observable universe.

HIERARCHY PROBLEMS IN STRING THEORY AND LARGE VOLUME MODELS

Nature generates many hierarchically different scales. It is necessary to explain where these scales come from and how they are related. Three such scales are the weak scale, the scale associated with axion physics, and the scale associated with neutrino masses. I review the large volume models that arise in flux compactifications of type IIB string theory and explain how an intermediate string scale can quantitatively explain the above three scales. The models also predict a new physical scale at 1 MeV, associated to a gravitationally coupled scalar.