Calculation of epsilon'/epsilon

I shortly review the present status of the theoretical calculations of epsilon'/epsilon and the comparison with the present experimental results. I discuss the role of higher order chiral corrections and in general of non-factorizable contributions for the explanation of the Delta I = 1/2 selection rule and direct CP violation in kaon decays. Still lacking reliable lattice calculations, analytic methods and phenomenological approaches are helpful in understanding correlations among theoretical effects and the experimental data. Substantial progress from lattice QCD is expected in the coming years.Comment: 10 pages, Invited talk at the 9th Int. Symposium on Heavy Flavour Physics, Pasadena, CA, 10-13 September 2001 Comments added on Table

Aspects of symmetry breaking in SO(10) GUTs

I review some recent results on the Higgs sector of minimal SO(10) grand unified theories both with and without supersymmetry. It is shown that nonsupersymmetric SO(10) with just one adjoint triggering the first stage of the symmetry breaking does provide a successful gauge unification when radiative corrections are taken into account in the scalar potential, while in the supersymmetric case it is argued that the troubles in achieving a phenomenologically viable breaking with representations up to the adjoint are overcome by considering the flipped SO(10) embedding of the hypercharge.Comment: 8 pages, 1 figure; prepared for the proceedings of DISCRETE'10 - Symposium on Prospects in the Physics of Discrete Symmetrie

N=1 Super QCD and Fractional Branes

We show how to get the one-loop beta function and the chiral anomaly of N=1 Super QCD from a stack of fractional N D3-branes localized inside the world-volume of 2M fractional D7-branes on the orbifold C^3/(Z_2 x Z_2). They are obtained by analyzing the classical supergravity background generated by such a brane configuration, in the spirit of the gauge/gravity correspondence.Comment: 4 pages, LaTeX. Talk given at the IXth International Symposium on Particles, Strings and Cosmology PASCOS '03, Mumbai-India, January 3-8 2003. To appear in a special issue of Praman

The Gauge/Gravity Correspondence for Non-Supersymmetric Theories

We review the string construction of the ``orientifold field theories'' and we show that for these theories the gauge/gravity correspondence is only valid for a large number of colours.Comment: 7 pages, Latex, Talk given at 37. International Symposium Ahrenshoop, Berlin, August 2004. Added references and acknowledgements; corrected typo

Why Michigan v. EPA Requires that the Meaning of the Cost/Rationality Nexus Be Clarified

This article examines the recent decision in Michigan v. EPA, in which the U.S. Supreme Court held that the EPA acted unreasonably in not considering costs at the listing phase of the regulation of power plants’ emissions under a specific provision of the Clear Air Act (CAA). In Michigan, the Court interpreted the applicable statutory provision based on the principles of rational administrative decision-making, thereby establishing a connection between cost consideration by administrative agencies and the principles of reasonable exercise of administrative discretion. We contend that Michigan failed to properly appreciate the logical and axiological connection between cost consideration and administrative rationality (i.e., the cost/rationality nexus). More specifically, the Court failed to distinguish between two independent steps of cost consideration: cost determination and cost quantification. Cost determination considers that one set of relevant interests must be made a cost upon someone else, and decides how to allocate rights between competing interests. This decision rests on political considerations and moral factors that are independent of the concept of cost. Cost quantification requires deliberating to what extent one set of interests should be made a cost upon someone else. Unlike cost determination, cost quantification is logically based on the concept of cost. Cost quantification assumes cost determination in order to function. The failure to appreciate this distinction led to illogical reasoning by the Court and to a decision that is inconsistent with Congress’ cost determination. This paper contributes to the legal-economic literature on cost-benefit analysis (CBA) by outlining a functional dimension of cost consideration by administrative agencies that is frequently overlooked in legal-economic literature. While CBA proponents often note that cost consideration provides agencies with a method for promoting social welfare maximization, we emphasize that cost consideration enhances the rationality of administrative action by ensuring a transparent and accountable definition of the set of relevant interests that underpins the definition of costs and benefits

Worldsheet instantons and (0,2) linear models

We study the stability of heterotic compactifications described by (0,2) gauged linear sigma models with respect to worldsheet instanton corrections to the space-time superpotential following the work of Beasley and Witten. We show that generic models elude the vanishing theorem proved there, and may not determine supersymmetric heterotic vacua. We then construct a subclass of linear models for which a vanishing theorem holds, generating an extensive list of consistent heterotic backgrounds.Comment: 21 pages; v2: minor correction

A (0,2) mirror duality

We construct a class of exactly solved (0,2) heterotic compactifications, similar to the (2,2) models constructed by Gepner. We identify these as special points in moduli spaces containing geometric limits described by non-linear sigma models on complete intersection Calabi-Yau spaces in toric varieties, equipped with a bundle whose rank is strictly greater than that of the tangent bundle. These moduli spaces do not in general contain a locus exhibiting (2,2) supersymmetry. A quotient procedure at the exactly solved point realizes the mirror isomorphism, as was the case for Gepner models. We find a geometric interpretation of the mirror duality in the context of hybrid models.Comment: 37 page

N=8 BPS black holes preserving 1/8 supersymmetry

In the context of N=8 supergravity we consider BPS black-holes that preserve 1/8 supersymmetry. It was shown in a previous paper that, modulo U-duality transformations of E_{7(7)} the most general solution of this type can be reduced to a black-hole of the STU model. In this paper we analize this solution in detail, considering in particular its embedding in one of the possible Special K\"ahler manifold compatible with the consistent truncations to N=2 supergravity, this manifold being the moduli space of the T^6/Z^3 orbifold, that is: SU(3,3)/SU(3)*U(3). This construction requires a crucial use of the Solvable Lie Algebra formalism. Once the group-theoretical analisys is done, starting from a static, spherically symmetric ans\"atz, we find an exact solution for all the scalars (both dilaton and axion-like) and for gauge fields, together with their already known charge-dependent fixed values, which yield a U-duality invariant entropy. We give also a complete translation dictionary between the Solvable Lie Algebra and the Special K\"ahler formalisms in order to let comparison with other papers on similar issues being more immediate. Although the explicit solution is given in a simplified case where the equations turn out to be more manageable, it encodes all the features of the more general one, namely it has non-vanishing entropy and the scalar fields have a non-trivial radial dependence.Comment: 29+1 pages, 1 Latex file; a misprint in the entropy formula, eq.(5.14), correcte