Classes of confining gauge field configurations

We present a numerical method to compute path integrals in effective SU(2) Yang-Mills theories. The basic idea is to approximate the Yang-Mills path integral by summing over all gauge field configurations, which can be represented as a linear superposition of a small number of localized building blocks. With a suitable choice of building blocks many essential features of SU(2) Yang-Mills theory can be reproduced, particularly confinement. The analysis of our results leads to the conclusion that topological charge as well as extended structures are essential elements of confining gauge field configurations.Comment: 18 pages, 16 figures, several sections adde

Low-energy modes of spin-imbalanced Fermi gases in BCS phase

The low-energy modes of a spin-imbalanced superfluid Fermi gas in the Bardeen-Cooper-Schrieffer (BCS) side are studied. The gas is assumed to be sufficiently dilute so that the pairing of atoms can be considered effective only in s-wave between fermions of different internal state. The order parameter at equilibrium is determined by the mean-field approximation, while the properties of the collective modes are calculated within a Gaussian approximation for the fluctuations of the order parameter. In particular we investigate the effects of asymmetry between the populations of the two different components and of temperature on the frequency and damping of collective modes. It is found that the temperature does not much affect the frequency and the damping of the modes, whereas an increase of the imbalance shifts the frequency toward lower values and enhances the damping sensitively. Besides the Bogoliubov-Anderson phonons, we observe modes at zero frequency for finite values of the wave-number. These modes indicate that an instability develops driving the system toward two separate phases, normal and superfluid.Comment: 7 pages, 4 figures, submitted to European Physical Journal D for publicatio

Fermions in the pseudoparticle approach

The pseudoparticle approach is a numerical technique to compute path integrals without discretizing spacetime. The basic idea is to integrate over those field configurations, which can be represented by a sum of a fixed number of localized building blocks (pseudoparticles). In a couple of previous papers we have successfully applied the pseudoparticle approach to pure SU(2) Yang-Mills theory. In this work we discuss how to incorporate fermionic fields in the pseudoparticle approach. To test our method, we compute the phase diagram of the 1+1-dimensional Gross-Neveu model in the large-N limit.Comment: 11 pages, 10 figure

Light Stop Searches at the LHC in Events with One Hard Photon or Jet and Missing Energy

Low energy supersymmetric models provide a solution to the hierarchy problem and also have the necessary ingredients to solve two of the most outstanding issues in cosmology: the origin of the baryon asymmetry and the source of dark matter. In the MSSM, weak scale generation of the baryon asymmetry may be achieved in the presence of light stops, with masses lower than about 130 GeV. Moreover, the proper dark matter density may be obtained in the stop-neutralino co-annihilation region, where the stop-neutralino mass difference is smaller than a few tens of GeV. Searches for scalar top quarks (stops) in pair production processes at the Tevatron and at the Large Hadron Collider (LHC) become very challenging in this region of parameters. At the LHC, however, light stops proceeding from the decay of gluino pairs may be identified, provided the gluino mass is smaller than about 900 GeV. In this article we propose an alternative method for stop searches in the co-annihilation region, based on the search for these particles in events with missing energy plus one hard photon or jet. We show that this method is quite efficient and, when complemented with ongoing Tevatron searches, allows to probe stop masses up to about 160 GeV, fully probing the region of parameters consistent with electroweak baryogenesis in the MSSM.Comment: 17 pages, 6 figure

The complementarity of LEP, the Tevatron and the LHC in the search for a light MSSM Higgs boson

We study the properties of the Higgs boson sector in the MSSM, putting special emphasis on radiative effects which can affect the discovery potential of the LHC, Tevatron and/or LEP colliders. We concentrate on the V b b-bar channel, with V=Z or W, and on the channels with diphoton final states, which are the dominant ones for the search for a light Standard Model Higgs boson at LEP/Tevatron and LHC, respectively. By analyzing the regions of parameter space for which the searches in at least one of these colliders can be particularly difficult, we demonstrate the complementarity of these three colliders in the search for a light Higgs boson which couples in a relevant way to the W and Z gauge bosons (and hence plays a relevant role in the mechanism of electroweak symmetry breaking).Comment: 35 pages, including 11 Postscript figures, using JHEP.cl

Direct printing of polymer microstructures on flat and spherical surfaces using a letterpress technique

We have developed a letterpress technique capable of printing polymer films with micrometer scale feature sizes onto flat or spherically shaped nonporous substrates. This printing technique deposits polymer only in desired regions thereby eliminating subsequent developing and subtraction steps. Flat or curved printing plates, which are fabricated from either rigid or deformable materials, are used to transfer thin molten polymer films onto flat target substrates. By deforming the printing plates into a spherical shape, it is also possible to print patterned films onto the concave side of a spherically deformed target substrate. These printed films serve as good resists for both wet chemical etching and reactive ion etching. Interferometric measurements of the polymer film thickness are used to probe physical mechanisms affecting printing instabilities, pattern fidelity, and edge resolution. Our experimental study indicates that this letterpress technique may prove suitable for high-throughput device fabrication involving large-area microelectronics