Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAxions and anomalous $U(1)$s
165
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Inspired by recent studies of high-scale decay constant or flavorful QCD axions, we review and clarify their existence in effective string models with anomalous $U(1)$ gauge groups. We find that such models, when coupled to charged scalars getting vacuum expectation values, always have one light axion, whose mass can only come from nonperturbative effects. If the main nonperturbative effect is from QCD, then it becomes a Peccei-Quinn axion candidate for solving the strong CP problem. We then study simple models with universal Green-Schwarz mechanism and only one charged scalar field: in the minimal gaugino condensation case the axion mass is tied to the supersymmetry breaking scale and cannot be light enough, but slightly refined models maintain a massless axion all the way down to the QCD scale. Both kinds of models can be extended to yield intermediate scale axion decay constants. Finally, we gauge flavorful axion models under an anomalous $U(1)$ and discuss the axion couplings which arise.
rate research
Read More
Massive $U(1)$ gauge theories featuring parametrically light vectors are suspected to belong in the Swampland of consistent EFTs that cannot be embedded into a theory of quantum gravity. We study four-dimensional, chiral $U(1)$ gauge theories that appear anomalous over a range of energies up to the scale of anomaly-cancelling massive chiral fermions. We show that such theories require to be UV-completed at a finite cutoff below which a radial mode must appear, and cannot be decoupled -- a Stuckelberg limit does not exist. When the infrared fermion spectrum contains a mixed $U(1)$-gravitational anomaly, this class of theories provides a toy model of a boundary into the Swampland, for sufficiently small values of the vector mass. In this context, we show that the limit of a parametrically light vector comes at the cost of a quantum gravity scale that lies parametrically below $M_{Pl}$, and our result provides field theoretic evidence for the existence of a Swampland of EFTs that is disconnected from the subset of theories compatible with a gravitational UV-completion. Moreover, when the low energy theory also contains a $U(1)^3$ anomaly, the Weak Gravity Conjecture scale makes an appearance in the form of a quantum gravity cutoff for values of the gauge coupling above a certain critical size.
We study the origin of electroweak symmetry under the assumption that $SU(4)_{rm C} times SU(2)_{rm L} times SU(2)_{rm R}$ is realized on a five-dimensional space-time. The Pati-Salam type gauge symmetry is reduced to $SU(3)_{rm C} times SU(2)_{rm L} times U(1)_{rm R} times U(1)_{rm B-L}$ by orbifold breaking mechanism on the orbifold $S^1/Z_2$. The breakdown of residual gauge symmetries occurs radiatively via the Coleman-Weinberg mechanism, such that the $U(1)_{rm R} times U(1)_{rm B-L}$ symmetry is broken down to $U(1)_{rm Y}$ by the vacuum expectation value of an $SU(2)_{rm L}$ singlet scalar field and the $SU(2)_{rm L} times U(1)_{rm Y}$ symmetry is broken down to the electric one $U(1)_{rm EM}$ by the vacuum expectation value of an $SU(2)_{rm L}$ doublet scalar field regarded as the Higgs doublet. The negative Higgs squared mass term is originated from an interaction between the Higgs doublet and an $SU(2)_{rm L}$ singlet scalar field as a Higgs portal. The vacuum stability is recovered due to the contributions from Kaluza-Klein modes of gauge bosons.
Since their proposal nearly half a century ago, physicists have sought axions in both high energy and condensed matter settings. Despite intense and growing efforts, to date experimental success has been limited, with the most prominent results arising in the context of topological insulators. Here we propose a novel mechanism whereby axions can be realized in quantum spin liquids. We discuss the necessary symmetry requirements and identify possible experimental realizations in candidate pyrochlore materials, such as ${text{Ba}_{3}text{Yb}_{2}text{Zn}_{5}text{O}_{11}}$. In this context, the axions couple both to the external and to the emergent electromagnetic fields. We show that the interaction between the axion and the emergent photon leads to a characteristic dynamical response, which can be measured experimentally in inelastic neutron scattering. This work sets the stage for studying axion electrodynamics in the highly tunable setting of frustrated magnets.
We investigate the properties of localized anomalous U(1)s in heterotic string theory on the orbifold T^6/Z_3. We argue that the local four dimensional and original ten dimensional Green-Schwarz mechanisms can be implemented simultaneously, making the theory manifestly gauge invariant everywhere, in the bulk and at the fixed points. We compute the shape of the Fayet-Iliopoulos tadpoles, and cross check this derivation for the four dimensional auxiliary fields by a direct calculation of the tadpoles of the internal gauge fields. Finally we study some resulting consequences for spontaneous symmetry breaking, and derive the profile of the internal gauge field background over the orbifold.
Embeddings of the standard model in type II string theory typically contain a variety of U(1) gauge factors arising from D-branes in the bulk. In general, there is no reason why only one of these - the one corresponding to weak hypercharge - should be massless. Observations require that standard model particles must be neutral (or have an extremely small charge) under additional massless U(1)s, i.e. the latter have to belong to a so called hidden sector. The exchange of heavy messengers, however, can lead to a kinetic mixing between the hypercharge and the hidden-sector U(1)s, that is testable with near future experiments. This provides a powerful probe of the hidden sectors and, as a consequence, of the string theory realisation itself. In the present paper, we show, using a variety of methods, how the kinetic mixing can be derived from the underlying type II string compactification, involving supersymmetric and nonsupersymmetric configurations of D-branes, both in large volumes and in warped backgrounds with fluxes. We first demonstrate by explicit example that kinetic mixing occurs in a completely supersymmetric set-up where we can use conformal field theory techniques. We then develop a supergravity approach which allows us to examine the phenomenon in more general backgrounds, where we find that kinetic mixing is natural in the context of flux compactifications. We discuss the phenomenological consequences for experiments at the low-energy frontier, searching for signatures of light, sub-electronvolt or even massless hidden-sector U(1) gauge bosons and minicharged particles.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
