Brane Worlds, the Cosmological Constant and String Theory

We argue that traditional methods of compactification of string theory make it very difficult to understand how the cosmological constant becomes zero. String inspired models can give zero cosmological constant after fine tuning but since string theory has no free parameters it is not clear that this is allowed. Brane world scenarios on the other hand while they do not answer the question as to why the cosmological constant is zero do actually allow a choice of integration constants that permit flat four space solutions. In this paper we discuss gauged supergravity realizations of such a world. To the extent that this starting point can be considered a low energy effective action of string theory (and there is some recent evidence supporting this) our model may be considered a string theory realization of this scenario.Comment: 18 pages, 5 figures. Shorter version and a few new comments adde

T. C. Flournoy letter to Moses Dawson

Letter from Flournoy (Cincinnati, Ohio) to Dawson (Cincinnati, Ohio) declining invitation to the Friends of Free Principles dinner in Cincinnati, Ohio on March 4, 1836.https://www.exhibit.xavier.edu/dawson_correspondence/1044/thumbnail.jp

Recreational Rights to the Dry Sand Beach in Florida: Property, Custom and Controversy

At the close of the 2018 legislative session Florida Governor Rick Scott signed HB 631 into law. Included in the bill, which addressed a number of issues relating to actions for ejectment from real property, was an amendment to the Florida Community Planning Act entitled “Establishment of Recreational Customary Use.” The new statute immediately created a sandstorm of controversy as the media seized on what many in the public perceived to be a land grab over the public’s right to recreate on Florida’s sandy beaches. As it turns out, the story is considerably more nuanced, and neither the advocates on both sides nor the media did the public any favors in the commentary and reporting on this issue. However, both the background to the legislation and subsequent events indicate that the public is rightly concerned about efforts to limit recreational access, some of which have been spurred or exacerbated by what had been a largely localized controversy. This paper begins by briefly describing the history of the current controversy, which had its origins in Walton County, Florida. The conflict centers on arguments about the public’s right to use the dry sand beach -- that area of the beach that is between the line of vegetation and the mean high tide line, and is often privately owned. We then discuss the broader legal context that gives rise to boundary disputes along dynamic shorelines and provide the essential policy-relevant facts concerning public and private sandy beach ownership. In order to fully understand the legal basis for the public’s claim of right to use the sandy beaches and the legislative response, we summarize the history of the relevant legal doctrine – known as customary use -- that came over from England during the post-colonial era and made its way into the law of a number of states, including Florida. We offer a detailed review of the Florida Supreme Court’s landmark case on the customary use doctrine along with subsequent lower court cases interpreting it. We then attempt to identify the legal issues that have created widespread confusion regarding the interplay among the common law property rights at issue, local ordinances that recognize and regulate those rights, and particularly, the state legislation that precipitated the widespread attention to and conflict over this issue -- HB 631, now codified in Fla. Stat. 163.035. After flagging several legal issues at the heart of the conflict, we provide an annotated summary of the statute that describes the interpretive issues it raises or may raise. We conclude by discussing some of the options available to the Florida legislature to resolve the sandstorm of controversy that HB 631 engendered

Asymmetric Orbifolds, Non-Geometric Fluxes and Non-Commutativity in Closed String Theory

In this paper we consider a class of exactly solvable closed string flux backgrounds that exhibit non-commutativity in the closed string coordinates. They are realized in terms of freely-acting asymmetric Z_N-orbifolds, which are themselves close relatives of twisted torus fibrations with elliptic Z_N-monodromy (elliptic T-folds). We explicitly construct the modular invariant partition function of the models and derive the non-commutative algebra in the string coordinates, which is exact to all orders in {\alpha}'. Finally, we relate these asymmetric orbifold spaces to inherently stringy Scherk-Schwarz backgrounds and non-geometric fluxes.Comment: 30 page

Closed String Tachyons and Semi-Classical Instabilities

We conjecture that the end point of bulk closed string tachyon decay at any non-zero coupling, is the annihilation of space time by Witten's bubble of nothing, resulting in a topological phase of the theory. In support of this we present a variety of situations in which there is a correspondence between the existence of perturbative tachyons in one regime and the semi-classical annihilation of space-time. Our discussion will include many recently investigated scenarios in string theory including Scherk-Schwarz compactifications, Melvin magnetic backgrounds, and noncompact orbifolds. We use this conjecture to investigate a possible web of dualities relating the eleven-dimensional Fabinger-Horava background with nonsupersymmetric string theories. Along the way we point out where our conjecture resolves some of the puzzles associated with bulk closed string tachyon condensation.Comment: 31 pages, 5 figures 3 figures added, typos corrected and references added. Discussion of Type 0/Heterotic s-duality extended and some other points clarified Revision of discussion on Fabinger-Horava string descendents, section on Scherk-Schwarz compactification of Horava-Witten removed, some references adde

T-duality in the weakly curved background

We consider the closed string propagating in the weakly curved background which consists of constant metric and Kalb-Ramond field with infinitesimally small coordinate dependent part. We propose the procedure for constructing the T-dual theory, performing T-duality transformations along coordinates on which the Kalb-Ramond field depends. The obtained theory is defined in the non-geometric double space, described by the Lagrange multiplier $y_\mu$ and its $T$-dual $\tilde{y}_\mu$. We apply the proposed T-duality procedure to the T-dual theory and obtain the initial one. We discuss the standard relations between T-dual theories that the equations of motion and momenta modes of one theory are the Bianchi identities and the winding modes of the other

The Ursinus Weekly, October 18, 1973

U.S.G.A. initiates tough new policy, vows good supervision of open houses • Ursinus admission requirements, unlike national trends, maintain standards • Cooperative atmosphere at education banquet • Ursinus karate club holds demonstration • Chapel program begins • College Union calendar full • Debating club forming; Mr. Perreten will head group • Editorial: On the outside looking in; Autumn at Ursinus • Letters to the Editor: Early riser protests; Declaration of independence; Compromise called for • Alumni Corner • Film: “Heavy Traffic” • Bagpiper Bud Hamilton plays at first College Union program • Ornithology - flocking together Supersax plays Bird • Library staff portrait: Mr. James Rue • Bearettes down Glassboro, F&M, and Bucks County • Another game, another loss • Cross country wins roll on • Soccer team now 3-2https://digitalcommons.ursinus.edu/weekly/1002/thumbnail.jp

Duality Invariant M-theory: Gauged supergravities and Scherk-Schwarz reductions

We consider the reduction of the duality invariant approach to M-theory by a U-duality group valued Scherk-Schwarz twist. The result is to produce potentials for gauged supergravities that are normally associated with non-geometric compactifications. The local symmetry reduces to gauge transformations with the gaugings exactly matching those of the embedding tensor approach to gauged supergravity. Importantly, this approach now includes a nontrivial dependence of the fields on the extra coordinates of the extended space.Comment: 22 pages Latex; v2: typos corrected and references adde

Matrix theory origins of non-geometric fluxes

We explore the origins of non-geometric fluxes within the context of M theory described as a matrix model. Building upon compactifications of Matrix theory on non-commutative tori and twisted tori, we formulate the conditions which describe compactifications with non-geometric fluxes. These turn out to be related to certain deformations of tori with non-commutative and non-associative structures on their phase space. Quantization of flux appears as a natural consequence of the framework and leads to the resolution of non-associativity at the level of the unitary operators. The quantum-mechanical nature of the model bestows an important role on the phase space. In particular, the geometric and non-geometric fluxes exchange their properties when going from position space to momentum space thus providing a duality among the two. Moreover, the operations which connect solutions with different fluxes are described and their relation to T-duality is discussed. Finally, we provide some insights on the effective gauge theories obtained from these matrix compactifications.Comment: 1+31 pages, reference list update

Mirrorfolds with K3 Fibrations

We study a class of non-geometric string vacua realized as completely soluble superconformal field theory (SCFT). These models are defined as `interpolating orbifolds' of $K3 \times S^1$ by the mirror transformation acting on the $K3$ fiber combined with the half-shift on the $S^1$-base. They are variants of the T-folds, the interpolating orbifolds by T-duality transformations, and thus may be called `mirrorfolds'. Starting with arbitrary (compact or non-compact) Gepner models for the $K3$ fiber, we construct modular invariant partition functions of general mirrorfold models. In the case of compact $K3$ fiber the mirrorfolds only yield non-supersymmetric string vacua. They exhibit IR instability due to winding tachyon condensation which is similar to the Scherk-Schwarz type circle compactification. When the fiber SCFT is non-compact (say, the ALE space in the simplest case), on the other hand, both supersymmetric and non-supersymmetric vacua can be constructed. The non-compact non-supersymmetric mirrorfolds can get stabilised at the level of string perturbation theory. We also find that in the non-compact supersymmeric mirrorfolds D-branes are {\em always} non-BPS. These D-branes can get stabilized against both open- and closed-string marginal deformations.Comment: Eqns (2.61) and (3.17) correcte