CPT and Other Symmetries in String/M Theory

We initiate a search for non-perturbative consistency conditions in M theory. Some non-perturbative conditions are already known in Type I theories; we review these and search for others. We focus principally on possible anomalies in discrete symmetries. It is generally believed that discrete symmetries in string theories are gauge symmetries, so anomalies would provide evidence for inconsistencies. Using the orbifold cosmic string construction, we give some evidence that the symmetries we study are gauged. We then search for anomalies in discrete symmetries in a variety of models, both with and without supersymmetry. In symmetric orbifold models we extend previous searches, and show in a variety of examples that all anomalies may be canceled by a Green-Schwarz mechanism. We explore some asymmetric orbifold constructions and again find that all anomalies may be canceled this way. Then we turn to Type IIB orientifold models where it is known that even perturbative anomalies are non-universal. In the examples we study, by combining geometric discrete symmetries with continuous gauge symmetries, one may define non-anomalous discrete symmetries already in perturbation theory; in other cases, the anomalies are universal. Finally, we turn to the question of CPT conservation in string/M theory. It is well known that CPT is conserved in all string perturbation expansions; here in a number of examples for which a non-perturbative formulation is available we provide evidence that it is conserved exactly.Comment: 52 pages.1 paragraph added in introduction to clarify assumption

Of CP and other Gauge Symmetries in String Theory

We argue that \CP is a gauge symmetry in string theory. As a consequence, \CP cannot be explicitly broken either perturbatively or non-pertubatively; there can be no non-perturbative \CP-violating parameters. String theory is thus an example of a theory where all $\theta$ angles arise due to spontaneous \CP violation, and are in principle calculable.Comment: 8 page

Sprayable Foams Based on an Amphiphilic Biopolymer for Control of Hemorrhage Without Compression

Hemorrhage (severe blood loss) from traumatic injury is a leading cause of death for soldiers in combat and for young civilians. In some cases, hemorrhage can be stopped by applying compression of a tourniquet or bandage at the injury site. However, the majority of hemorrhages that prove fatal are “non-compressible”, such as those due to an internal injury in the truncal region. Currently, there is no effective way to treat such injuries. In this initial study, we demonstrate that a sprayable polymer-based foam can be effective at treating bleeding from soft tissue without the need for compression. When the foam is sprayed into an open cavity created by injury, it expands and forms a self-supporting barrier that counteracts the expulsion of blood from the cavity. The active material in this foam is the amphiphilic biopolymer, hydrophobically modified chitosan (hmC), which physically connects blood cells into clusters via hydrophobic interactions (the hemostatic mechanism of hmC is thus distinct from the natural clotting cascade, and it works even with heparinized or citrated blood). The amphiphilic nature of hmC also allows it to serve as a stabilizer for the bubbles in the foam. We tested the hmC-based hemostatic foam for its ability to arrest bleeding from an injury to the liver in pigs. Hemostasis was achieved within minutes after application of the hmC foams (without the need for external compression). The total blood loss was 90% lower with the hmC foam relative to controls