Non-supersymmetric Orientifolds of Gepner Models

Starting from a previously collected set of tachyon-free closed strings, we search for N=2 minimal model orientifold spectra which contain the standard model and are free of tachyons and tadpoles at lowest order. For each class of tachyon-free closed strings -- bulk supersymmetry, automorphism invariants or Klein bottle projection -- we do indeed find non-supersymmetric and tachyon free chiral brane configurations that contain the standard model. However, a tadpole-cancelling hidden sector could only be found in the case of bulk supersymmetry. Although about half of the examples we have found make use of branes that break the bulk space-time supersymmetry, the resulting massless open string spectra are nevertheless supersymmetric in all cases. Dropping the requirement that the standard model be contained in the spectrum, we find chiral tachyon and tadpole-free solutions in all three cases, although in the case of bulk supersymmetry all massless spectra are supersymmetric. In the other two cases we find truly non-supersymmetric spectra, but a large fraction of them are nevertheless partly or fully supersymmetric at the massless level.Comment: 13 pages, 4 figure

Classification of Simple Current Invariants

We summarize recent work on the classification of modular invariant partition functions that can be obtained with simple currents in theories with a center (Z_p)^k with p prime. New empirical results for other centers are also presented. Our observation that the total number of invariants is monodromy-independent for (Z_p)^k appears to be true in general as well. (Talk presented in the parallel session on string theory of the Lepton-Photon/EPS Conference, Geneva, 1991.)Comment: 8 page

Minimal Models from W-Constrained Hierarchies via the Kontsevich-Miwa Transform

A direct relation between the conformal formalism for 2d-quantum gravity and the W-constrained KP hierarchy is found, without the need to invoke intermediate matrix model technology. The Kontsevich-Miwa transform of the KP hierarchy is used to establish an identification between W constraints on the KP tau function and decoupling equations corresponding to Virasoro null vectors. The Kontsevich-Miwa transform maps the $W^{(l)}$-constrained KP hierarchy to the $(p^\prime,p)$ minimal model, with the tau function being given by the correlator of a product of (dressed) $(l,1)$ (or $(1,l)$) operators, provided the Miwa parameter $n_i$ and the free parameter (an abstract $bc$ spin) present in the constraints are expressed through the ratio $p^\prime/p$ and the level $l$.Comment: 11 pp REVISED (minor changes in the presentation, easier to read

Adding value to urban spaces. Two examples from Lisbon

Through a comparative analysis of two urban spaces located in the city of Lisbon, Portugal, I intend to demonstrate how some values can be added to space in order to attract certain residents, investors or interests, and how these urban spaces make use of these values to differentiate and promote themselves in various ways. In considering the gentrification process in the city centre and the construction of a spatial and social neighborhood identity in a more peripheral area, I focus on the urban middle classes and some social strategies of belonging.info:eu-repo/semantics/publishedVersio

Constraints on extra dimensions from precision molecular spectroscopy

Accurate investigations of quantum level energies in molecular systems are shown to provide a test ground to constrain the size of compactified extra dimensions. This is made possible by the recent progress in precision metrology with ultrastable lasers on energy levels in neutral molecular hydrogen (H$_2$, HD and D$_2$) and the molecular hydrogen ions (H$_2^+$, HD$^+$ and D$_2^+$). Comparisons between experiment and quantum electrodynamics calculations for these molecular systems can be interpreted in terms of probing large extra dimensions, under which conditions gravity will become much stronger. Molecules are a probe of space-time geometry at typical distances where chemical bonds are effective, i.e. at length scales of an \AA. Constraints on compactification radii for extra dimensions are derived within the Arkani-Hamed-Dimopoulos-Dvali framework, while constraints for curvature or brane separation are derived within the Randall-Sundrum framework. Based on the molecular spectroscopy of D$_2$ molecules and HD$^+$ ions, the compactification size for seven extra dimensions (in connection to M-theory defined in 11 dimensions) of equal size is shown to be limited to $R_7 < 0.6 \mu$m. While limits on compactification sizes of extra dimensions based on other branches of physics are compared, the prospect of further tightening constraints from the molecular method is discussed

Between doorkeeper apartments and housemaid rooms: ways of living in a changing Lisbon

If the city is a repository of different ways of dwelling that reflect social heterogeneity in terms of class, economic power and social status, the house, as the primary space of intimate and family life, is still the most faithful reflection of these same ways of living and their changes over time. This article proposes to approach processes of social and architectural transformation that marked the domestic space and the culture of living in Lisbon in the mid-20th century. One of the objectives is to illustrate not only how the houses –their architecture, their living– reflect the social, cultural and symbolic values of an era, but also how certain historic characters often underestimated –such as housemaids and doorkeepers– can assume greater prominence in the understanding of the home culture and ways of inhabiting.info:eu-repo/semantics/acceptedVersio