427 research outputs found
4D Effective Theory and Geometrical Approach
We consider the 4D effective theory for the light Kaluza-Klein (KK) modes.
The heavy KK mode contribution is generally needed to reproduce the correct
physical predictions: an equivalence, between the effective theory and the
D-dimensional (or geometrical) approach to spontaneous symmetry breaking (SSB),
emerges only if the heavy mode contribution is taken into account. This happens
even if the heavy mode masses are at the Planck scale. In particular, we
analyze a 6D Einstein-Maxwell model coupled to a charged scalar and fermions.
Moreover, we briefly review non-Abelian and supersymmetric extensions of this
theory.Comment: 7 pages, 2 figures. Proceeding for the Cairo International Conference
on High Energy Physics (CICHEP II), 14 - 17 January 200
Chiral Asymmetry from a 5D Higgs Mechanism
An intriguing feature of the Standard Model is that the representations of
the unbroken gauge symmetries are vector-like whereas those of the
spontaneously broken gauge symmetries are chiral. Here we provide a toy model
which shows that a natural explanation of this property could emerge in higher
dimensional field theories and discuss the difficulties that arise in the
attempt to construct a realistic theory. An interesting aspect of this type of
models is that the 4D low energy effective theory is not generically gauge
invariant. However, the non-invariant contributions to the observable
quantities are very small, of the order of the square of the ratio between the
light particle mass scale and the Kaluza-Klein mass scale. Remarkably, when we
take the unbroken limit both the chiral asymmetry and the non-invariant terms
disappear.Comment: 30 pages, 5 figures, uses axodraw.sty. Extended version, matches the
article published on JHE
Relaxing Lorentz invariance in general perturbative anomalies
We analyze the role of Lorentz symmetry in the perturbative non-gravitational
anomalies for a single family of fermions. The theory is assumed to be
translational invariant, power-counting renormalizable and based on a local
action, but is allowed to have general Lorentz violating operators. We study
the conservation of global and gauge currents associate with general internal
symmetry groups and find, by using a perturbative approach, that Lorentz
symmetry does not participate in the clash of symmetries that leads to the
anomalies. We first analyze the triangle graphs and prove that there are
regulators for which the anomalous part of the Ward identities exactly
reproduces the Lorentz invariant case. Then we show, by means of a regulator
independent argument, that the anomaly cancellation conditions derived in
Lorentz invariant theories remain necessary ingredients for anomaly freedom.Comment: 18 pages, 1 figure. Few comments added. Article published in Physical
Review
On the Decoupling of Heavy Modes in Kaluza-Klein Theories
In this paper we examine the 4-dimensional effective theory for the light
Kaluza-Klein (KK) modes. Our main interest is in the interaction terms. We
point out that the contribution of the heavy KK modes is generally needed in
order to reproduce the correct predictions for the observable quantities
involving the light modes. As an example we study in some detail a
6-dimensional Einstein-Maxwell theory coupled to a charged scalar and fermions.
In this case the contribution of the heavy KK modes are geometrically
interpreted as the deformation of the internal space.Comment: 38 pages, 1 figur
Aspects of Physics with Two Extra Dimensions
In this thesis we discuss some aspects concerning the construction of a 4D
effective theory derived from higher dimensional (in particular 6D) models. The
first part is devoted to the study of how the heavy Kaluza-Klein modes
contribute to the low energy dynamics of the light modes. The second part
concerns the analysis of the spectrum arising from non standard
compactifications of 6D minimal gauged supergravities, involving a warp factor
and conical defects in the internal manifold. We also review some of the
background material.Comment: PhD Thesis, 142 pages, 2 Postscript figures, uses axodraw.st
Gravitational waves from fundamental axion dynamics
A totally asymptotically free QCD axion model, where all couplings flow to zero in the infinite energy limit, was recently formulated. A very interesting feature of this fundamental theory is the ability to predict some low-energy observables, like the masses of the extra fermions and scalars. Here we find and investigate a region of the parameter space where the Peccei-Quinn (PQ) symmetry is broken quantum mechanically through the Coleman-Weinberg mechanism. This results in an even more predictive framework: the axion sector features only two independent parameters (the PQ symmetry breaking scale and the QCD gauge coupling). In particular, we show that the PQ phase transition is strongly first order and can produce gravitational waves within the reach of future detectors. The predictivity of the model leads to a rigid dependence of the phase transition (like its duration and the nucleation temperature) and the gravitational wave spectrum on the PQ symmetry breaking scale and the QCD gauge coupling
Axion–sterile neutrino dark matter
Extending the standard model with three right-handed neutrinos and a simple QCD axion sector can account for neutrino oscillations, dark matter and baryon asymmetry; at the same time, it solves the strong CP problem, stabilizes the electroweak vacuum and can implement critical Higgs inflation (satisfying all current observational bounds). We perform here a general analysis of dark matter (DM) in such a model, which we call the a nu MSM. Although critical Higgs inflation features a (quasi) inflection point of the inflaton potential, we show that DM cannot receive a contribution from primordial black holes in the a nu MSM. This leads to a multicomponent axion-sterile neutrino DM and allows us to relate the axion parameters, such as the axion decay constant, to the neutrino parameters. We include several DM production mechanisms: the axion production via misalignment and decay of topological defects as well as the sterile neutrino production through the resonant and non-resonant mechanisms and in the recently proposed CPT-symmetric universe
Running with Rugby Balls: Bulk Renormalization of Codimension-2 Branes
We compute how one-loop bulk effects renormalize both bulk and brane
effective interactions for geometries sourced by codimension-two branes. We do
so by explicitly integrating out spin-zero, -half and -one particles in
6-dimensional Einstein-Maxwell-Scalar theories compactified to 4 dimensions on
a flux-stabilized 2D geometry. (Our methods apply equally well for D dimensions
compactified to D-2 dimensions, although our explicit formulae do not capture
all divergences when D>6.) The renormalization of bulk interactions are
independent of the boundary conditions assumed at the brane locations, and
reproduce standard heat-kernel calculations. Boundary conditions at any
particular brane do affect how bulk loops renormalize this brane's effective
action, but not the renormalization of other distant branes. Although we
explicitly compute our loops using a rugby ball geometry, because we follow
only UV effects our results apply more generally to any geometry containing
codimension-two sources with conical singularities. Our results have a variety
of uses, including calculating the UV sensitivity of one-loop vacuum energy
seen by observers localized on the brane. We show how these one-loop effects
combine in a surprising way with bulk back-reaction to give the complete
low-energy effective cosmological constant, and comment on the relevance of
this calculation to proposed applications of codimension-two 6D models to
solutions of the hierarchy and cosmological constant problems.Comment: 42 pages + appendices. This is the final version which appears in
JHE
(In)equivalence of metric-affine and metric effective field theories
In a geometrical approach to gravity the metric and the (gravitational) connection can be independent and one deals with metric-affine theories. We construct the most general action of metric-affine effective field theories, including a generic matter sector, where the connection does not carry additional dynamical fields. Among other things, this helps in identifying the complement set of effective field theories where there are other dynamical fields, which can have an interesting phenomenology. Within the latter set, we study in detail a vast class where the Holst invariant (the contraction of the curvature with the Levi-Civita antisymmetric tensor) is a dynamical pseudoscalar. In the Einstein-Cartan case (where the connection is metric compatible and fermions can be introduced) we also comment on the possible phenomenological role of dynamical dark photons from torsion and compute interactions of the above-mentioned pseudoscalar with a generic matter sector and the metric. Finally, we show that in an arbitrary realistic metric-affine theory featuring a generic matter sector the equivalence principle always emerges at low energies without the need to postulate it
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