Multi-modal digital documentation and visualization of the unesco painted churches in troodos (cyprus)

In 1985, the World Heritage Committee inscribed the site “Painted Churches in the Troodos Region” of the Republic of Cyprus on the UNESCO World Heritage List. The latter included nine Byzantine and Post Byzantine Churches to which a tenth church was added in 2001. In the framework of the IH-AT project, all the churches and the premises in their proximities were analysed using a wide array of non-destructive digital methodologies coupled with more traditional art-historical studies. Image- and Range-based techniques were used to document all the morphological features of the buildings with the final goal of understanding their humble architecture. Additionally, a Ground Penetrating Radar (GPR) was performed to investigate the presence of buried structures that, according to historical sources, were once surrounding the religious sites. For the exploitation and visualization of the extensive database by the scientific community and the public at large, a web portal comprised of reliable and efficient technology-ready tools have been developed. The proposed methodology was implemented to provide new insights on the churches’ architectural features; confirm the presence or absence of buried remains of archaeological interest; and help heritage professionals, with lack or minimal programming skills, to customize online visualizations of 3D interactive models

D-instantons and Closed String Tachyons in Misner Space

We investigate closed string tachyon condensation in Misner space, a toy model for big bang universe. In Misner space, we are able to condense tachyonic modes of closed strings in the twisted sectors, which is supposed to remove the big bang singularity. In order to examine this, we utilize D-instanton as a probe. First, we study general properties of D-instanton by constructing boundary state and effective action. Then, resorting to these, we are able to show that tachyon condensation actually deforms the geometry such that the singularity becomes milder.Comment: 24 pages, 1 figure, minor change

D-branes in a Big Bang/Big Crunch Universe: Nappi-Witten Gauged WZW Model

We study D-branes in the Nappi-Witten model, which is a gauged WZW model based on (SL(2,R) x SU(2)) / (U(1) x U(1)). The model describes a four dimensional space-time consisting of cosmological regions with big bang/big crunch singularities and static regions with closed time-like curves. The aim of this paper is to investigate by D-brane probes whether there are pathologies associated with the cosmological singularities and the closed time-like curves. We first classify D-branes in a group theoretical way, and then examine DBI actions for effective theories on the D-branes. In particular, we show that D-brane metric from the DBI action does not include singularities, and wave functions on the D-branes are well behaved even in the presence of closed time-like curves.Comment: 50 pages, 2 figures, minor change

Closed strings in Misner space: a toy model for a Big Bounce ?

Misner space, also known as the Lorentzian orbifold $R^{1,1}/boost$, is one of the simplest examples of a cosmological singularity in string theory. In this lecture, we review the semi-classical propagation of closed strings in this background, with a particular emphasis on the twisted sectors of the orbifold. Tree-level scattering amplitudes and the one-loop vacuum amplitude are also discussed.Comment: 30 pages, 3 figures, to appear in the Proceedings of the NATO ASI and EC Summer School ``String Theory: from Gauge Interactions to Cosmology'', Cargese, France, June 7-19, 200

Flux Backgrounds in 2D String Theory

We study RR flux backgrounds in two dimensional type 0 string theories. In particular, we study the relation between the 0A matrix model and the extremal black hole in two dimensions. Using T-duality we find a dual flux background in type 0B theory and propose its matrix model description. When the Fermi level is set to zero this system remains weakly coupled and exhibits a larger symmetry related to the structure of flux vacua. Finally, we construct a two dimensional type IIB background as an orbifold of the 0B background.Comment: Harvmac, 40 pages, 6 figs, minor changes, references adde

A Matrix Model Dual of Type 0B String Theory in Two Dimensions

We propose that type 0B string theory in two dimensions admits a dual description in terms of a one dimensional bosonic matrix model of a hermitian matrix. The potential in the matrix model is symmetric with respect to the parity-like Z_2 transformation of the matrix. The two sectors in the theory, namely the NSNS and RR scalar sectors correspond to two classes of operators in the matrix model, even and odd under the Z_2 symmetry respectively. We provide evidence that the matrix model successfully reconstructs the perturbative S-matrix of the string theory, and reproduces the closed string emission amplitude from unstable D-branes. Following recent work in two dimensional bosonic string, we argue that the matrix model can be identified with the theory describing N unstable D0-branes in type 0B theory. We also argue that type 0A theory is described in terms of the quantum mechanics of brane-antibrane systems.Comment: Latex, 20 pages, typos corrected, explanations added, references adde

Matrix Model and Time-like Linear Dilaton Matter

We consider a matrix model description of the 2d string theory whose matter part is given by a time-like linear dilaton CFT. This is equivalent to the c=1 matrix model with a deformed, but very simple fermi surface. Indeed, after a Lorentz transformation, the corresponding 2d spacetime is a conventional linear dilaton background with a time-dependent tachyon field. We show that the tree level scattering amplitudes in the matrix model perfectly agree with those computed in the world-sheet theory. The classical trajectories of fermions correspond to the decaying D-branes in the time-like linear dilaton CFT. We also discuss the ground ring structure. Furthermore, we study the properties of the time-like Liouville theory by applying this matrix model description. We find that its ground ring structure is very similar to that of the minimal string.Comment: 30 pages, harvmac, typos corrected, acknowledgements and comments added(v2), published version (v3

Testing QCD with Hypothetical Tau Leptons

We construct new tests of perturbative QCD by considering a hypothetical tau lepton of arbitrary mass, which decays hadronically through the electromagnetic current. We can explicitly compute its hadronic width ratio directly as an integral over the e^+ e^- annihilation cross section ratio, R_{e^+e^-}. Furthermore, we can design a set of commensurate scale relations and perturbative QCD tests by varying the weight function away from the form associated with the V-A decay of the physical tau. This method allows the wide range of the R_{e^+e^-} data to be used as a probe of perturbative QCD.Comment: 4 pages, 4 figure

Mesonic Chiral Rings in Calabi-Yau Cones from Field Theory

We study the half-BPS mesonic chiral ring of the N=1 superconformal quiver theories arising from N D3-branes stacked at Y^pq and L^abc Calabi-Yau conical singularities. We map each gauge invariant operator represented on the quiver as an irreducible loop adjoint at some node, to an invariant monomial, modulo relations, in the gauged linear sigma model describing the corresponding bulk geometry. This map enables us to write a partition function at finite N over mesonic half-BPS states. It agrees with the bulk gravity interpretation of chiral ring states as cohomologically trivial giant gravitons. The quiver theories for L^aba, which have singular base geometries, contain extra operators not counted by the naive bulk partition function. These extra operators have a natural interpretation in terms of twisted states localized at the orbifold-like singularities in the bulk.Comment: Latex, 25pgs, 12 figs, v2: minor clarification

Non-Minimal Sneutrino Inflation, Peccei-Quinn Phase Transition and non-Thermal Leptogenesis

We consider a phenomenological extension of the minimal supersymmetric standard model which incorporates non-minimal chaotic inflation, driven by a quartic potential associated with the lightest right-handed sneutrino. Inflation is followed by a Peccei-Quinn phase transition based on renormalizable superpotential terms, which resolves the strong CP and mu problems of the minimal supersymmetric standard model provided that one related parameter of the superpotential is somewhat small. Baryogenesis occurs via non-thermal leptogenesis, which is realized by the inflaton decay. Confronting our scenario with the current observational data on the inflationary observables, the baryon assymetry of the universe, the gravitino limit on the reheating temperature and the upper bound on the light neutrino masses, we constrain the effective Yukawa coupling involved in the decay of the inflaton to relatively small values and the inflaton mass to values lower than 10^12 GeV.Comment: 21 pages including 3 figures; Final versio