This thesis work analyzes basic field theoretical aspects of a class of models motivated by orientifold vacua of string theory and some of their phenomenological applications at the Large Hadron Collider. They extend the gauge structure of the Standard Model by anomalous extra U(1) symmetries, which involve Stuckelberg axions for anomaly cancellation and are accompanied by Chern-Simons interactions. In particular, these effective actions are characterized by a physical pseudoscalar (the axi-Higgs) in the CP-odd spectrum, which has the properties of a generalized Peccei-Quinn axion, with independent mass and couplings to the gauge fields. Amplitudes mediated by anomalous gauge interactions are studied at the new collider in some specific channels such as Drell-Yan and double prompt-photon and shown to be small. Finally, we address the problem of the relation between the Green-Schwarz and the Wess-Zumino mechanism(s) for anomaly cancellations in effective lagrangeans involving anomalous gauge interactions, with their gauge symmetry restored either with local or non-local counterterms and identify some unitarity bounds in the Wess-Zumino case. These are due to the presence of anomaly poles in scattering amplitudes mediated by the anomaly (BIM amplitudes) and whose cancellation requires necessarly non-local counterterms. While the axi-Higgs appears in the Wess-Zumino case, two axion-like particles are needed for the cancellation of the gauge anomalies at all scales, one of them being a ghost.
We describe a simple connection between the Froggatt-Nielsen, Stueckelberg and Higgs mechanisms, all three of them combined in a consistent way. This is illustrated in the context of a class of generalizations of the Standard Model with a gauge structure extended by a certain number of anomalous U(1) factors. These are built in the effective action in a way that gauge invariance and unitarity are preserved. Among other features, a physical axion with properties different from those of a Peccei-Quinn axion emerges.
A Stueckelberg extension of the MSSM with only one abelian vector and one chiral superfield as an alternative to an abelian extension with Higgs scalars is presented. The bosonic sector contains a new gauge boson Z' which is a sharp resonance, and a new CP-even scalar, which combines with the MSSM Higgs bosons to produce three neutral CP-even massive states. The neutral fermionic sector has two additional fermions which mix with the four MSSM neutralinos to produce an extended 6x6 neutralino mass matrix. For the case when the LSP is composed mostly of the Stueckelberg fermions, the LSP of the …
In 1938, Stueckelberg introduced a scalar field which makes an Abelian gauge theory massive but preserves gauge invariance. The Stueckelberg mechanism is the introduction of new fields to reveal a symmetry of a gauge--fixed theory. We first review the Stueckelberg mechanism in the massive Abelian gauge theory. We then extend this idea to the standard model, stueckelberging the hypercharge U(1) and thus giving a mass to the physical photon. This introduces an infrared regulator for the photon in the standard electroweak theory, along with a modification of the weak mixing angle accompanied by a…
We study the non-abelian $SU(2)_D$ extension of the $U(1)_D$ Stueckelberg portal, which plays a role of the mediator between the Standard Model (SM) and Dark Sector (DS). This portal is specified by the Stueckelberg mechanism for generation of dark gauge boson masses. Proposed $U(1)_D\times SU(2)_D$ Stueckelberg portal has a connection with SM matter fields in analogy with Familon Model. We derive bounds on the couplings of dark portal bosons and SM particles, which govern diagonal and non-diagonal flavor transitions of quarks and leptons.
String theory constructions using D-brane physics offer a framework where ingredients like extra abelian factors in the gauge group, more than one Higgs doublet and a generalized Green-Schwarz mechanism appear at the same time. Motivated by works towards the direction of obtaining the Standard Model in orientifold constructions, we study in the present work a Stueckelberg extension of the two-Higgs-doublet model. The distinctive features of our model are i) a sharp decay width for the heavy gauge boson, and ii) a charged Higgs boson having two main decay channels at tree level with equal branc…
We discuss the problem of unitarity for Yang-Mills theory in the Landau gauge with a mass term a la Stueckelberg. We assume that the theory (non-renormalizable) makes sense in some subtraction scheme (in particular the Slavnov-Taylor identities should be respected!) and we devote the paper to the study of the space of the unphysical modes. We find that the theory is unitary only under the hypothesis that the 1-PI two-point function of the vector mesons has no poles (at p^2=0). This normalization condition might be rather crucial in the very definition of the theory. With all these provisos the…
Abelian vector bosons can get massive through the Stueckelberg mechanism without spontaneous symmetry breaking via condensation of Higgs scalar fields. This appears very naturally in models derived from string theory and supergravity. The simplest scenarios of this type consist of extensions of the Standard Model (SM) or the minimal supersymmetric standard model (MSSM) by an extra U(1)_X gauge group with Stueckelberg type couplings. For the SM, the physical spectrum is extended by a massive neutral gauge boson Z' only, while the extension of the MSSM contains a CP-even neutral scalar and two e…
Stueckelberg mechanism introduces a scalar field, known as Stueckelberg field, so that gauge symmetry is preserved in the massive abelian gauge theory. In this work, we show that the role of the Stueckelberg field is similar to the Kulish and Faddeev coherent state approach to handle infrared (IR) divergences. We expect that the light-front quantum electrodynamics (LFQED) with Stueckelberg field must be IR finite in the massless limit of the gauge boson. We have explicitly shown the cancellation of IR divergences in the relevant diagrams contributing to self-energy and vertex correction at lea…
A overview is given of the recent developments in the $U(1)_X$ Stueckelberg extensions of the Standard Model and of MSSM where all the Standard Model particles are neutral under the $U(1)_X$ but an axion which is absorbed is charged under both $U(1)_X$ and $U(1)_Y$ and acts as the connector field coupling the Standard Model sector with the Stueckelberg sector. Coupled with the usual Higgs mechanism that breaks the $SU(2)_L\times U(1)_Y$ gauge symmetry, this scenario produces mixings in the neutral gauge boson sector generating an extra $Z'$ boson. The couplings of the extra $Z'$ to the Standar…
An extension of the standard model of electro-weak interactions by an extra abelian gauge boson is given, in which the extra gauge boson and the hypercharge gauge boson both couple to an axionic scalar in a form that leads to a Stueckelberg mass term. The theory leads to a massive Z$'$ whose couplings to fermions are uniquely determined and suppressed by small mixing angles. Such a Z$'$ could have low mass and appear in $e^+e^-$ collisions as a sharp resonance. The branching ratios into $f\bar f$ species, and the forward-backward asymmetry are found to have distinctive features. The model also…
We investigate the decoupling of heavy right handed neutrinos in the context of an SO(10) GUT model, where a remnant anomalous symmetry is $U(1)_{X}$. In this model the see-saw mechanism which generates the neutrino masses is intertwined with the Stueckelberg mechanism, which leaves the CP-odd phase of a very heavy Higgs in the low energy spectrum as an axion-like particle. Such pseudoscalar is predicted to be ultralight, in the $10^{-20}$ eV mass range. In this scenario, the remnant anomalous $X$ symmetry of the particles of the Standard Model is interpreted as due to the incomplete decouplin…
A detailed analysis of a Stueckelberg extension of the electro-weak gauge group with an extra U(1) factor is presented for the Standard Model as well as for the MSSM. The extra gauge boson gets massive through a Stueckelberg type coupling to a pseudo-scalar, instead of a Higgs effect. This new massive neutral gauge boson Z' has vector and axial vector couplings uniquely different from those of conventional extra abelian gauge bosons, such as appear e.g. in GUT models. The extended MSSM furthermore contains two extra neutralinos and one extra neutral CP-even scalar, the latter with a mass large…
We analyze the conditions under which some supersymmetric generalizations of a class of models descending from string theory allow an axion in the physical spectrum, due to the presence of anomalous abelian gauge interactions. The gauge structure of these constructions involve the Stueckelberg supermultiplet and a supersymmetric version of the Wess-Zumino term for anomaly cancellation. While these conditions are not satisfied by the MSSM superpotential, we show that an axion-like particle appears in the spectrum if extra Standard Model singlets are present. We show that the minimal requirement…
We analyze the quantum consistency of anomalous abelian models and of their effective field theories, rendered anomaly-free by a Wess-Zumino term, in the case of multiple abelian symmetries. These models involve the combined Higgs-Stuckelberg mechanism and predict a pseudoscalar axion-like field that mixes with the goldstones of the ordinary Higgs sector. We focus our study on the issue of unitarity of these models both before and after spontaneous symmetry breaking and detail the set of Ward identities and the organization of the loop expansion in the effective theory. The analysis is perform…
The axion particle may or may not exist, but the axion field can be used, as shown here, in an explicitly local formulation of a chiral U(1) gauge theory with both classical and quantum gauge invariance. Nonabelian analogues of axion fields, which have recently been introduced, can be used, together with their special symmetries, in a similar construction of nonabelian chiral gauge theories. As in known cases, the gauge symmetry is broken and the gauge boson acquires a mass by swallowing the axions which are therefore not physical in this construction.
We elaborate on an extension of the Standard Model with a gauge structure enlarged by a single anomalous U(1), where the presence of a Wess-Zumino term is motivated by the Green-Schwarz mechanism of string theory. The additional gauge interaction is anomalous and requires an axion for anomaly cancelation. The pseudoscalar implements the Stückelberg mechanism and undergoes mixing with the standard Higgs sector to render the additional U(1) massive. We consider a 2-Higgs doublet model. We show that the anomalous effective vertices involving neutral currents are potentially observable. We clarify…
We give a simplified proof for the perturbative renormalizability of theories with massive vector particles. For renormalizability it is sufficient that the vector particle is treated as an gauge field, corresponding to an Abelian gauge group. Contrary to the non-Abelian case one does not need the Higgs mechanism to create the appropriate mass terms. The proof uses ``Stueckelberg's trick'' and the Ward-Takahashi identities from local Abelian gauge invariance. The simplification is due to the fact that, again contrary to the non-Abelian case, no BRST analysis is needed.
The solution to the Strong CP problem is analysed within the Minimal Flavour Violation (MFV) context. An Abelian factor of the complete flavour symmetry of the fermionic kinetic terms may play the role of the Peccei-Quinn symmetry in traditional axion models. Its spontaneous breaking, due to the addition of a complex scalar field to the Standard Model scalar spectrum, generates the MFV axion, which may redefine away the QCD theta parameter. It differs from the traditional QCD axion for its couplings that are governed by the fermion charges under the axial Abelian symmetry. It is also distinct …
The effects of possible explicit violation of the Peccei-Quinn symmetry responsible for the solution of the strong CP problem are studied in supersymmetric models. It is shown that automatic models with an abelian $U(1)$ gauge symmetry are easy to construct both in the context of fundamental and composite models of axions. It is argued that it is preferable to use abelian rather than nonabelian gauge groups in order to obtains automatic symmetries. A composite model with no exact $R$ symmetry is studied and it is found that, unlike common belief, supersymmetry is broken.
In axion gauge field inflation an axion-like particle driving cosmic inflation is coupled to the Chern-Simons density of an Abelian or non-Abelian gauge group. In the case of a non-Abelian gauge group, this can lead to the formation of a stable, homogeneous and isotropic gauge field background. We study the dynamics of the inflaton and gauge fields in terms of the two effective coupling parameters: the gauge coupling and the axion decay constant. Starting from the Bunch-Davies vacuum in the far past, we find that the non-trivial gauge field background arises only significantly after the cosmic…
We combine two popular extensions of beyond the Standard Model physics within the framework of intersecting D6-brane models: discrete Zn symmetries and Peccei-Quinn axions. The underlying natural connection between both extensions is formed by the presence of massive U(1) gauge symmetries in D-brane model building. Global intersecting D6-brane models on toroidal orbifolds of the type T6/Z2N and T6/Z2xZ2M with discrete torsion offer excellent playgrounds for realizing these extensions. A generation-dependent Z2 symmetry is identified in a global Pati-Salam model, while global left-right symmetr…
A pseudoscalar inflaton $φ$, coupled to the topological charge density $F\tilde{F}$ of a non-Abelian sector, can decay to gauge bosons ($φ\to g g $), which may thermalize rapidly. The friction felt by $φ$ is then increased by non-Abelian "strong sphalerons", leading to a self-amplifying process that can efficiently heat up the medium. We determine a lower bound for the gravitational wave production rate from such a process, originating via hydrodynamic fluctuations and particle collisions, in terms of a minimal number of parameters. Only a moderate fraction of energy density is converted to gr…
We present a supersymmetric extension of the Standard Model (USSM-A) with an anomalous U(1) and Stueckelberg axions for anomaly cancellation, generalizing similar non-supersymmetric constructions. The model, built by a bottom-up approach, is expected to capture the low-energy supersymmetric description of axionic symmetries in theories with gauged anomalous abelian interactions, previously explored in the non-supersymmetric case for scenarios with intersecting branes. The choice of a USSM-like superpotential, with one extra singlet superfield and an extra abelian symmetry, allows a physical ax…
We study the production and backreaction of massive vector-like fermions in the background of a classical SU(2) gauge field during axion-driven inflation. We demonstrate all ultraviolet divergences due to the interactions with the fermions can be absorbed by renormalization of the axion wavefunction and the gauge coupling. The effects of the fermion-axion interaction vanish in the massless limit as required by symmetry. For very massive fermions, contact interactions are induced between the axion, the gauge field and the gravitational field. In this massive limit, we find the usual axion-gauge…
Multimodal axion emissions from Abelian-Higgs cosmic strings
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University（东北大学前沿跨学科研究院）；Department of Physics, Tohoku University（东北大学物理系）；Cosmology, Gravity, and Astroparticle Physics Group, Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS)（基础科学研究院宇宙理论物理中心宇宙学、引力与天体粒子物理组）
We present a brief overview of axion models associated to anomalous abelian (gauge) symmetries, discussing their main phenomenological features. Among these, the mechanism of vacuum misalignment introduced at the QCD and at the electroweak phase transitions, with the appearance of periodic potentials, responsible for the generation of a mass for these types of axions.
Classical equipartition dynamics between axions and non-Abelian gauge fields
Walter Burke Institute for Theoretical Physics, California Institute of Technology（加州理工学院沃尔特·伯克理论物理研究所）；Fakultät für Physik, Universität Bielefeld（比勒费尔德大学物理学院）；AEC, Institute for Theoretical Physics, University of Bern（伯尔尼大学理论物理研究所）
We study cosmological field configurations (solutions) in a model in which the pseudo-scalar phase of a complex field couples to the Pontryagin density of a massive non-abelian gauge field, in analogy to how the Peccei-Quinn axion field couples to the $SU(3)$-color gauge field of QCD. Assuming that the self-interaction potential of the complex scalar field has the typical {\it Mexican hat} form, we find that the radial fluctuations of this field can act as {\it Dark Matter}, while its phase may give rise to tracking {\it Dark Energy}. In our model, Dark-Energy domination will, however, not con…
Pseudoscalars appearing in particle physics are reviewd systematically. From the fundamental point of view at an ultra-violat completed theory, they can be light if they are realized as pseudo-Goldstone bosons of some spontaneously broken global symmetries. The spontaneous breaking scale is parametrized by the decay constant $f$. The global symmetry is defined by the lowest order terms allowed in the effective theory consistent with the gauge symmetry in question. Since any global symmetry is known to be broken at least by quantum gravitational effects, all pseudoscalars should be massive. The…
Axion is a promising candidate of dark matter. After the Peccei-Quinn symmetry breaking, axion strings are formed and attached by domain walls when the temperature of the universe becomes comparable to the QCD scale. Such objects can cause cosmological disasters if they are long-lived. As a solution for it, the Lazarides-Shafi mechanism is often discussed through introduction of a new non-Abelian (gauge) symmetry. We study this mechanism in detail and show configuration of strings and walls. Even if Abelian axion strings with a domain wall number greater than one are formed in the early univer…
In our previous work, we found new types of the cosmic string solutions in the Abelian-Higgs model with an enhanced $U(1)$ global symmetry. We dubbed those solutions as the compensated/uncompensated strings. The compensated string is similar to the conventional cosmic string in the Abrikosov-Nielsen-Olesen (ANO) string, around which only the would-be Nambu-Goldstone (NG) boson winds. Around the uncompensated string, on the other hand, the physical NG boson also winds, where the physical NG boson is associated with the spontaneous breaking of the enhanced symmetry. Our previous simulation in th…
We show that axions interacting with abelian gauge fields obtain a potential from loops of magnetic monopoles. This is a consequence of the Witten effect: the axion field causes the monopoles to acquire an electric charge and alters their energy spectrum. The axion potential can also be understood as a type of instanton effect due to a Euclidean monopole worldline winding around its dyon collective coordinate. We calculate this effect, which has features in common with both nonabelian instantons and Euclidean brane instantons. To provide consistency checks, we argue that this axion potential v…
The baryon asymmetry of the universe may be explained by rotations of the QCD axion in field space and baryon number violating processes. We consider the minimal extension of the Standard Model by a non-Abelian gauge interaction, $SU(2)_R$, whose sphaleron process violates baryon number. Assuming that axion dark matter is also created from the axion rotation by the kinetic misalignment mechanism, the mass scale of the $SU(2)_R$ gauge boson is fixed as a function of the QCD axion decay constant, and vise versa. Significant portion of the parameter space has already been excluded by new gauge bo…
Gauge-flation, non-Abelian gauge field inflation, which was introduced in arXiv:1102.1513 and analyzed more thoroughly in arXiv:1102.1932, is a model of inflation driven by non-Abelian gauge fields minimally coupled to Einstein gravity. In this model certain rotationally invariant combination of gauge fields play the role of inflaton. Recently, the chromo-natural inflation model was proposed arXiv:1202.2366 which besides the non-Abelian gauge fields also involve an axion field. In this short note we show that the model involving axions, indeed allows for various slow-roll trajectories for diff…
We use a lattice simulation to study a model of axion inflation where the inflaton is coupled to a U(1) gauge field through Chern-Simons interaction. These kinds of models have already been studied with a lattice simulation in the context of reheating. In this work, we focus on the deep inflationary phase and discuss the new aspects that need to be considered in order to simulate gauge fields in this regime. Our main result is reproducing with precision the growth of the gauge field on the lattice induced by the rolling of the axion on its potential, thus recovering the results of linear pertu…
Chromo-natural inflation is a model where non-abelian gauge fields are sustained by the coupling of the axion with the gauge field through the Chern-Simons term. While minimal warm inflation is a model where the axion produces a thermal bath of non-abelian gauge particles through the Chern-Simons term. Since both axion inflation models are based on the same action, a natural question is if those are compatible or not. We study axion inflation with the Chern-Simons term and find that chromo-natural inflation can accommodate radiation with a temperature much larger than the Hubble parameter duri…
We study the impact of sphaleron-induced thermal friction on the axion dark-matter abundance due to the interaction of an axion-like particle (ALP) with a dark non-abelian gauge sector in a secluded thermal bath. Thermal friction can either enhance the axion relic density by delaying the onset of oscillations or suppress it by damping them. We derive an analytical formula for the \emph{frictional adiabatic invariant}, which remains constant along the axion evolution and which allows us to compute the axion relic density in a general set-up. Even in the most minimal scenario, in which a single …
We present a model that solves the strong CP problem via an axion parametrically heavier than the standard one. Within this picture the Standard Model quarks are embedded into a larger non-abelian Grand Color group that at high scales splits into ordinary QCD and an additional confining dynamics under which exotic chiral fermions are charged. Crucially, the vacuum expectation value of the axion is automatically relaxed to zero because the only renormalizable source of explicit CP violation, beyond those encoded in the topological angles, is contained in the Standard Model Yukawa couplings, and…
We consider six-dimensional supergravity compactified on orbifolds with Wilson lines and bulk flux. Torus Wilson lines are decomposed into Wilson lines around the orbifold fixed points, and twisted boundary conditions of matter fields are related to fractional localized flux. Both, orbifold singularities and flux lead to chiral fermions in four dimensions. We show that in addition to the standard bulk and fixed point anomalies the Green-Schwarz term also cancels the four-dimensional anomaly induced by the flux background. The two axions contained in the antisymmetric tensor field both contribu…
Motivated by the Xenon1T excess in electron-recoil measurements, we investigate the prospects of probing axion-like particles (ALP) in lepton flavor violation experiments. In particular, we identify such ALP as a pseudo-Goldstone from the spontaneous breaking of the flavor symmetries that explain the mixing structure of the Standard Model leptons. We present the case of the flavor symmetries being a non-Abelian U(2) and the ALP originating from its U(1) subgroup, which is anomaly-free with the Standard Model group. We build two explicit realistic examples that reproduce leptonic masses and mix…
Real time evolution of classical gauge fields is relevant for a number of applications in particle physics and cosmology, ranging from the early Universe to dynamics of quark-gluon plasma. We present a lattice formulation of the interaction between a $shift$-symmetric field and some $U(1)$ gauge sector, $a(x)\tilde{F}_{μν}F^{μν}$, reproducing the continuum limit to order $\mathcal{O}(dx_μ^2)$ and obeying the following properties: (i) the system is gauge invariant and (ii) shift symmetry is exact on the lattice. For this end we construct a definition of the {\it topological number density} $Q =…
We outline some general features of possible extensions of the Standard Model that include anomalous U(1) gauge symmetries, a certain number of axions and their mixings with the CP-odd Higgs sector. As previously shown, after the mixing one of the axions becomes a physical pseudoscalar (the axi-Higgs) that can take the role of a modified QCD axion. It can be driven to be very light by the same non-perturbative effects that are held responsible for the solution of the strong CP-problem. At the same time the axi-Higgs has a sizeable gauge interaction, which is not allowed to the Peccei-Quinn axi…
Energy and momentum dependence of the soft-axion interaction rate
SUBATECH, Nantes Université, IMT Atlantique, IN2P3/CNRS（南特大学、IMT大西洋学院、法国国家科学研究中心/欧洲核子研究实验粒子物理研究所）；AEC, Institute for Theoretical Physics, University of Bern（伯尔尼大学理论物理研究所）；Instituto de Física, Universidade de São Paulo（圣保罗大学物理研究所）
Strong (sublattice or tower) formulations of the Weak Gravity Conjecture (WGC) imply that, if a weakly coupled gauge theory exists, a tower of charged particles drives the theory to strong coupling at an ultraviolet scale well below the Planck scale. This tower can consist of low-spin states, as in Kaluza-Klein theory, or high-spin states, as with weakly-coupled strings. We provide a suggestive bottom-up argument based on the mild $p$-form WGC that, for any gauge theory coupled to a fundamental axion through a $θF \wedge F$ term, the tower is a stringy one. The charge-carrying string states at…
We study UV-complete Froggatt-Nielsen-like models for the generation of mass and mixing hierarchies, assuming that the integrated heavy fields are chiral with respect to an abelian Froggatt-Nielsen symmetry. It modifies the mixed anomalies with respect to the Standard Model gauge group, which opens up the possibility to gauge the Froggatt-Nielsen symmetry without the need to introduce additional spectator fermions, while keeping mass matrices usually associated to anomalous flavour symmetries. We give specific examples where this happens, and we study the flavourful axion which arises from an …
We study the trispectrum of the gravitational waves (GWs) generated through the dynamics of an axionic spectator field and SU(2) gauge fields during inflation. In non-Abelian gauge theory, the gauge fields have four-point self-interactions, which induce the tree-level GW trispectrum. We formulate this type of the GW trispectrum including the non-dynamical contributions and evaluate it in the equilateral limit as a unique signal of this model. We find that the ratio of the GW trispectrum to the cube of the scalar power spectrum can be as large as $\mathcal{O}(10^6)$ in the viable parameter spac…
We illustrate the structure and the main phenomenological features of a supersymmetric model (the USSM-A) built following a bottom-up approach and containing an anomalous abelian gauge symmetry. This model supports a gauged axion in its spectrum and provides a generalization of the global (supersymmetric) Peccei-Quinn construction. Complete simulations of the neutralino relic density are performed. Bounds from CAST and WMAP, combined with dark matter simulations, provide significant constraints on the scale of the interactions between the axion and the gauge fields.
We discuss the $U(1)_X$ extensions of the standard model with focus on the Stueckelberg mechanism for mass growth for the extra $U(1)_X$ gauge boson. The assumption of an axionic connector field which carries dual U(1) quantum numbers, i.e., quantum numbers for the hypercharge $U(1)_Y$ and for the hidden sector gauge group $U(1)_X$, allows a non-trivial mixing between the mass growth for the neutral gauge vector bosons in the $SU(2)_L\times U(1)_Y$ sector and the mass growth for the vector boson by the \st mechanism in the $U(1)_X$ sector. This results in an extra $Z'$ which can be very narrow…
We study a non-Abelian gauge theory with a pseudo scalar coupling ϕε^{μναβ} F_{μν}^a F_{αβ}^a in the case where a constant chromo-electric, or chromo-magnetic, strength expectation value is present. We compute the interaction potential within the framework of gauge-invariant, path-dependent, variables formalism. While in the case of a constant chromo-electric field strength expectation value the static potential remains Coulombic, in the case of a constant chromo-magnetic field strength the potential energy is the sum of a Coulombic and a linear potentials, leading to the confinement of static…
Extensions of the Standard Model with extra neutral currents due to additional anomalous abelian gauge factors are considered. We summarize the main features of the effective action associated to these theories. They are characterized by an axion-like particle (the {\em axi-higgs}) which can be (almost) massless, with its mass generated non-perturbatively in the QCD vacuum as for an ordinary Peccei-Quinn axion, but that can also mix with the scalars of the Higgs sector, becoming a heavy axion. We briefly describe the interplay between the electroweak and the QCD sectors in these types of theor…
