C. C. Nishi

The Quest for an Intermediate-Scale Accidental Axion and Further ALPs

A bstractThe recent detection of the cosmic microwave background polarimeter experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically excludes all plausible axion models where its decay constant is above 1013 GeV. Moreover, there are strong theoretical, astrophysical, and cosmological motivations for models involving, in addition to the axion, also axion-like particles (ALPs), with decay constants in the intermediate scale range, between 109 GeV and 1013 GeV. Here, we present a general analysis of models with an axion and further ALPs and derive bounds on the relative size of the axion and ALP photon (and electron) coupling. We discuss what we can learn from measurements of the axion and ALP photon couplings about the fundamental parameters of the underlying ultraviolet completion of the theory. For the latter we consider extensions of the Standard Model in which the axion and the ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global chiral U(1) (Peccei-Quinn (PQ)) symmetries, occurring accidentally as low energy remnants from exact discrete symmetries. In such models, the axion and the further ALP are protected from disastrous explicit symmetry breaking effects due to Planck-scale suppressed operators. The scenarios considered exploit heavy right handed neutrinos getting their mass via PQ symmetry breaking and thus explain the small mass of the active neutrinos via a seesaw relation between the electroweak and an intermediate PQ symmetry breaking scale. For a number of explicit models, we determine the parameters of the low-energy effective field theory describing the axion, the ALPs, and their interactions with photons and electrons, in terms of the input parameters, in particular the PQ symmetry breaking scales. We show that these models can accommodate simultaneously an axion dark matter candidate, an ALP explaining the anomalous transparency of the universe for γ-rays, and an ALP explaining the recently reported 3.55 keV gamma line from galaxies and clusters of galaxies, if the respective decay constants are of intermediate scale. Moreover, they do not suffer severely from the domain wall problem.

S 4 flavored C P symmetry for neutrinos

, this almost completes the CP-conserving part of the lepton mixing matrix,under the assumption that there are no sterile neutrinos. This narrows the focus of the eld to three remainingunknowns of neutrino avor physics: (i) Dirac versus Majorana nature of the neutrino masses, (ii) mass hierarchyamong them|namely, normal versus inverted|and (iii) leptonic CP-violating phases. The last item has two partsto it: Dirac phase, which is analogous to the CKM phase in quark sector, and Majorana phases, which are exclusiveto the neutrino sector for Majorana neutrinos. The former can be measured in oscillation experiments whereas thelatter may play a role in neutrinoless double beta decay searches. All these phases may play a role in understandingthe origin of matter.On the theoretical side, despite such a vast amount of information, the nature of BSM physics responsible forneutrino avor properties remains largely unknown and is the subject of extensive investigation. There are twogeneric approaches: one based on symmetries in the lepton sector leaving the quarks aside and a second one based ongrand uni ed theories where both quarks and leptons are considered together.The quark-lepton uni ed grand-uni cation-based approach not only provides a very natural embedding of the seesawmechanism to explain small neutrino masses but also, in a very economical class of renormalizable SO(10) models,turns out to be very predictive. Indeed, the recently measured value of

Properties of the general N-Higgs-doublet model. I. The orbit space

We study the scalar sector of the general N-Higgs-doublet model via geometric constructions in the space of gauge orbits. We give a detailed description of the shape of the orbit space both for general N and, in more detail, for N = 3. We also comment on remarkable analogies between NHDM and quantum information theory.

An

We propose a simple extension of the electroweak standard model based on the discrete

S_3

S_3

Model for Lepton Mass Matrices with Nearly Minimal Texture

symmetry that is capable of realizing a nearly minimal Fritzsch-type texture for the Dirac mass matrices of both charged leptons and neutrinos. This is achieved with the aid of additional

New and trivial CP symmetry for extended A

Z_5

_4

and

flavor

Z_3

Mu-tau reflection symmetry with a texture-zero

symmetries, one of which can be embedded in