Closed-String Tachyon Condensation and the Worldsheet Super-Higgs Effect

Alternative gauge choices for worldsheet supersymmetry can elucidate dynamical phenomena obscured in the usual superconformal gauge. In the particular example of the tachyonic $E_8$ heterotic string, we use a judicious gauge choice to show that the process of closed-string tachyon condensation can be understood in terms of a worldsheet super-Higgs effect. The worldsheet gravitino assimilates the goldstino and becomes a dynamical propagating field. Conformal, but not superconformal, invariance is maintained throughout.Comment: 4 pages; v2: typos corrected, a reference added; v3: final version, to appear in Phys. Rev. Lett. (abstract and intro modified for a broader audience

A sensitive S-band noise receiver developed for the Mariner Mars 1964 spacecraft program

Sensitive S-band noise receiver for Mariner Mars 1964 spacecraft progra

Traffic flow densities in large transport networks

We consider transport networks with nodes scattered at random in a large domain. At certain local rates, the nodes generate traffic flowing according to some navigation scheme in a given direction. In the thermodynamic limit of a growing domain, we present an asymptotic formula expressing the local traffic flow density at any given location in the domain in terms of three fundamental characteristics of the underlying network: the spatial intensity of the nodes together with their traffic generation rates, and of the links induced by the navigation. This formula holds for a general class of navigations satisfying a link-density and a sub-ballisticity condition. As a specific example, we verify these conditions for navigations arising from a directed spanning tree on a Poisson point process with inhomogeneous intensity function.Comment: 20 pages, 7 figure

Large deviations in relay-augmented wireless networks

We analyze a model of relay-augmented cellular wireless networks. The network users, who move according to a general mobility model based on a Poisson point process of continuous trajectories in a bounded domain, try to communicate with a base station located at the origin. Messages can be sent either directly or indirectly by relaying over a second user. We show that in a scenario of an increasing number of users, the probability that an atypically high number of users experiences bad quality of service over a certain amount of time, decays at an exponential speed. This speed is characterized via a constrained entropy minimization problem. Further, we provide simulation results indicating that solutions of this problem are potentially non-unique due to symmetry breaking. Also two general sources for bad quality of service can be detected, which we refer to as isolation and screening.Comment: 28 pages, 5 figures; corrected several misprint

Large-deviation principles for connectable receivers in wireless networks

We study large-deviation principles for a model of wireless networks consisting of Poisson point processes of transmitters and receivers, respectively. To each transmitter we associate a family of connectable receivers whose signal-to-interference-and-noise ratio is larger than a certain connectivity threshold. First, we show a large-deviation principle for the empirical measure of connectable receivers associated with transmitters in large boxes. Second, making use of the observation that the receivers connectable to the origin form a Cox point process, we derive a large-deviation principle for the rescaled process of these receivers as the connection threshold tends to zero. Finally, we show how these results can be used to develop importance-sampling algorithms that substantially reduce the variance for the estimation of probabilities of certain rare events such as users being unable to connectComment: 29 pages, 2 figure

Letter from Charles [A.] Keeler to John Muir, 1901 Feb 23.

Dunedin, N. Z.,February 23rdf 1901.My dear Mr. Muir:Very often since we have been on this interesting voyage we have thought and spoken of you. Of course I have been constantly making comparisons of everything with Alaska and to speak of the Harriman Expedition is to recall my roommate during those two delightful months on the Elder. How you would enjoy this New Zealand country! The coast is not unlike the California shore - bleak brown hills over which the wind sweeps and the fog drifts - but in a week we shall be amid the wonderful lakes surrounded by snow-capped mountains, and with densely forested shores. I hope to visit Southerland Falls, 1900 ft. high, and anticipate much of interest in the excursions amid the mountains.We spent over two months at Tahiti, studying the life of the tropics - the mountains and the plains covered with brilliant verdure, the sparkling sea of the brightest blue, the ring of coral reef encircling the lagoon, with white breakers ever dashing upon it, and the bright people so gentle and friendly in their ways, with bronzed skin and wreathes of flowers. It was beautiful and charming for a time, but the life of the tropics is so utterly corrupt that we were glad enough to be off exploring fresh fields and pastures new.We have been hard at work, striving to portray the life we have seen. Louise has made over 60 drawings and I have written industriously. Our present plan is to remain three months in New Zealand, but beyond that we are uncertain. The Oceanic Steamship Company have written to London asking for our transportation home via London, visiting India and Egypt on the way. If this is granted you will not see us for many a long day, but if they refuse it we shall return by Samoa and Honolulu, reaching home about the first of August.I hope you are well and writing away at your visions of mountain and forest. We should be most happy to have a line from you way off here, but in any event we feel sure you have not forgotten us in our flight across the seas.With kindest regards to Mrs. Muir and the girls, from us both, believe me,Very sincerely your friend,Charles KeelerOur address isCare Union Steamship Co., Auckland, N.Z.0284

M-Theory Through the Looking Glass: Tachyon Condensation in the E_8 Heterotic String

We study the spacetime decay to nothing in string theory and M-theory. First we recall a nonsupersymmetric version of heterotic M-theory, in which bubbles of nothing -- connecting the two E_8 boundaries by a throat -- are expected to be nucleated. We argue that the fate of this system should be addressed at weak string coupling, where the nonperturbative instanton instability is expected to turn into a perturbative tachyonic one. We identify the unique string theory that could describe this process: The heterotic model with one E_8 gauge group and a singlet tachyon. We then use worldsheet methods to study the tachyon condensation in the NSR formulation of this model, and show that it induces a worldsheet super-Higgs effect. The main theme of our analysis is the possibility of making meaningful alternative gauge choices for worldsheet supersymmetry, in place of the conventional superconformal gauge. We show in a version of unitary gauge how the worldsheet gravitino assimilates the goldstino and becomes dynamical. This picture clarifies recent results of Hellerman and Swanson. We also present analogs of R_\xi gauges, and note the importance of logarithmic CFT in the context of tachyon condensation.Comment: 36 pages, 1 figur