Quark confinement , topological susceptibility and all that in 4 dimensional gluodynamics

We discuss a few tightly connected problems, such as the $U(1)$ problem, confinement, the $\theta$ -dependence within a framework of the dynamical toron approach. We calculate two fundamental characteristics of the theory: the vacuum expectation value (vev) of the Wilson loop and the topological susceptibility. The analogy with well known 2+1 dimensional QED which exhibits confinement phenomenon is also discussed.Comment: 14 pages, CERN-TH 6564/9

Once more on θ\theta-vacua in 2+12+1 dimensional QED and 3+1 dimensional gluodynamics

Two different but tightly connected problems, $U(1)$ and strong CP violation problems, are discussed in two different models which exhibit both asymptotic freedom and confinement. One of them is the 3d Polyakov's model of compact QED and the other is 4d gluodynamics. It is shown that although both these models possess the long range interactions of the topological charges, only in the former case physics does not depend on $\theta$; while the latter exhibits an explicit $\theta$- dependence. The crucial difference is due to the observation, that the pseudoparticles of 4d gluodynamics possess an aditional quantum number, apart of the topological charge $Q$ .Comment: 15 page

Evolution of String-Wall Networks and Axionic Domain Wall Problem

We study the cosmological evolution of domain walls bounded by strings which arise naturally in axion models. If we introduce a bias in the potential, walls become metastable and finally disappear. We perform two dimensional lattice simulations of domain wall networks and estimate the decay rate of domain walls. By using the numerical results, we give a constraint for the bias parameter and the Peccei-Quinn scale. We also discuss the possibility to probe axion models by direct detection of gravitational waves produced by domain walls.Comment: 19 pages, 7 figures; revised version of the manuscript, accepted for publication in JCA

Fractons in Twisted Multiflavor Schwinger Model

We consider two-dimensional QED with several fermion flavors on a finite spatial circle. A modified version of the model with {\em flavor-dependent} boundary conditions $\psi_p(L) = e^{2\pi ip/ N} \psi_p(0)$, $p = 1, \ldots , N$ is discussed ($N$ is the number of flavors). In this case a non-contactable contour in the space of the gauge fields is {\em not} determined by large gauge transformations. The Euclidean path integral acquires the contribution from the gauge field configurations with fractional topological charge. The configuration with $\nu = 1/N$ is responsible for the formation of the fermion condensate $\langle\bar{\psi}_p \psi_p\rangle_0$. The condensate dies out as a power of $L^{-1}$ when the length $L$ of the spatial box is sent to infinity. Implications of this result for non-abelian gauge field theories are discussed in brief.Comment: 29 pages, 3 figures available upon request, Report TPI-MINN-94-24-T Plain LATE

Axionic dark energy and a composite QCD axion

We discuss the idea that the model-independent (MI) axion of string theory is the source of quintessential dark energy. The scenario is completed with a composite QCD axion from hidden sector squark condensation that could serve as dark matter candidate. The mechanism relies on the fact that the hidden sector anomaly contribution to the composite axion is much smaller than the QCD anomaly term. This intuitively surprising scenario is based on the fact that below the hidden sector scale $\Lambda_h$ there are many light hidden sector quarks. Simply, by counting engineering dimensions the hidden sector instanton potential can be made negligible compared to the QCD anomaly term.Comment: 9 pages, 7 figure

Chiral Condensate and Short-Time Evolution of QCD(1+1) on the Light-Cone

Chiral condensates in the trivial light-cone vacuum emerge if defined as short-time limits of fermion propagators. In gauge theories, the necessary inclusion of a gauge string in combination with the characteristic light-cone infrared singularities contain the relevant non-perturbative ingredients responsible for formation of the condensate, as demonstrated for the 't Hooft model.Comment: 4 pages, Revtex

Small steps towards Grand Unification and the electron/positron excesses in cosmic-ray experiments

We consider a small extension of the standard model by adding two Majorana fermions; those are adjoint representations of the SU(2)_L and SU(3)_c gauge groups of the standard model. In this extension, the gauge coupling unification at an energy scale higher than 10^{15} GeV is realized when the masses of the triplet and the octet fermions are smaller than 10^4 GeV and 10^{12} GeV, respectively. We also show that an appropriate symmetry ensures a long lifetime of the neutral component of the triplet fermion whose thermal relic density naturally explains the observed dark matter density. The electron/positron excesses observed in recent cosmic-ray experiments can be also explained by the decay of the triplet fermion.Comment: 11 pages, 5 figure

New constraints for heavy axion-like particles from supernovae

We derive new constraints on the coupling of heavy pseudoscalar (axion-like) particles to photons, based on the gamma ray flux expected from the decay of these particles into photons. After being produced in the supernova core, these heavy axion-like particles would escape and a fraction of them would decay into photons before reaching the Earth. We have calculated the expected flux on Earth of these photons from the supernovae SN 1987A and Cassiopeia A and compared our results to data from the Fermi Large Area Telescope. This analysis provides strong constraints on the parameter space for axion-like particles. For a particle mass of 100 MeV, we find that the Peccei-Quinn constant, f_a, must be greater than about 10^{15} GeV. Alternatively, for fa=10^{12} GeV, we exclude the mass region between approximately 100 eV and 1 GeV.Comment: 14 pages, 4 figures. Version published in JCAP. Major changes in the exposition. Added a figure. Added appendix. Minor changes in the results. Some changes in the bibliograph

Confusing the extragalactic neutrino flux limit with a neutrino propagation limit

We study the possible suppression of the extragalactic neutrino flux due to a nonstandard interaction during its propagation. In particular, we study neutrino interaction with an ultra-light scalar field dark matter. It is shown that the extragalactic neutrino flux may be suppressed by such an interaction, leading to a new mechanism to reduce the ultra-high energy neutrino flux. We study both the cases of non-self-conjugate as well as self-conjugate dark matter. In the first case, the suppression is independent of the neutrino and dark matter masses. We conclude that care must be taken when explaining limits on the neutrino flux through source acceleration mechanisms only, since there could be other mechanisms for the reduction of the neutrino flux.Comment: 15 pages, 4 figures. Important changes implemented. Abstract modified. Conclusions remain. To be published in JCA

The Partonic Nature of Instantons

In both Yang-Mills theories and sigma models, instantons are endowed with degrees of freedom associated to their scale size and orientation. It has long been conjectured that these degrees of freedom have a dual interpretation as the positions of partonic constituents of the instanton. These conjectures are usually framed in d=3+1 and d=1+1 dimensions respectively where the partons are supposed to be responsible for confinement and other strong coupling phenomena. We revisit this partonic interpretation of instantons in the context of d=4+1 and d=2+1 dimensions. Here the instantons are particle-like solitons and the theories are non-renormalizable. We present an explicit and calculable model in d=2+1 dimensions where the single soliton in the CP^N sigma-model can be shown to be a multi-particle state whose partons are identified with the ultra-violet degrees of freedom which render the theory well-defined at high energies. We introduce a number of methods which reveal the partons inside the soliton, including deforming the sigma model and a dual version of the Bogomolnyi equations. We conjecture that partons inside Yang-Mills instantons hold the key to understanding the ultra-violet completion of five-dimensional gauge theories.Comment: 28 pages. v3: extra references and comments. Mathematica notebooks for the figures can be downloaded from http://www.damtp.cam.ac.uk/user/dt281/parton.htm