Yangians in Deformed Super Yang-Mills Theories

We discuss the integrability structure of deformed, four-dimensional N=4 super Yang-Mills theories using Yangians. We employ a recent procedure by Beisert and Roiban that generalizes the beta deformation of Lunin and Maldacena to produce N=1 superconformal gauge theories, which have the superalgebra SU(2,2|1)xU(1)xU(1). The deformed theories, including those with the more general twist, were shown to have retained their integrable structure. Here we examine the Yangian algebra of these deformed theories. In a five field subsector, we compute the two cases of SU(2)xU(1)xU(1)xU(1) and SU(2|1)xU(1)xU(1) as residual symmetries of SU(2,2|1)xU(1)xU(1). We compute a twisted coproduct for these theories, and show that only for the residual symmetry do we retain the standard coproduct. The twisted coproduct thus provides a method for symmetry breaking. However, the full Yangian structure of SU(2|3) is manifest in our subsector, albeit with twisted coproducts, and provides for the integrability of the theory.Comment: 17 page

Gravitational anomaly and fundamental forces

I present an argument, based on the topology of the universe, why there are three generations of fermions. The argument implies a preferred gauge group of SU(5), but with SO(10) representations of the fermions. The breaking pattern SU(5) to SU(3)xSU(2)xU(1) is preferred over the pattern SU(5) to SU(4)xU(1). On the basis of the argument one expects an asymmetry in the early universe microwave data, which might have been detected already.Comment: Contribution to the 2nd School and Workshop on Quantum Gravity and Quantum Geometry. Corfu, september 13-20 2009. 10 page

Removing Singularities

Big bang/crunch curvature singularities in exact CFT string backgrounds can be removed by turning on gauge fields. This is described within a family of {SL(2)xSU(2)xU(1)_x}/{U(1)xU(1)} quotient CFTs. Uncharged incoming wavefunctions from the ``whiskers'' of the extended universe can be fully reflected if and only if a big bang/crunch curvature singularity, from which they are scattered, exists. Extended BTZ-like singularities remain as long as U(1)_x is compact.Comment: 21 pages, harvma

The torment of exile and the aesthetics of nostalgia : transnational Chinese neo-romanticism in Xu Xu’s post-war fiction

Physical exile certainly was a painful reality for Xu Xu. Restorative nostalgia might to some extent have informed his literary activity in those years. However, nostalgia in Xu Xu’s postwar fiction, I will argue in this paper, constitutes above all the expression of a quest for a purely aesthetic utopia that had already begun to take shape in his pre-war oeuvre and that came to full fruition in his post-war fiction. By analyzing a number of Xu Xu’s novellas from Hong Kong, such as Bird Talk, The Other Shore 彼岸 (1951), and The All-Souls Tree 百靈樹 (1954), I will show that nostalgia in Xu’s fiction is ultimately time and place unspecific, and that Xu himself was aware of the limits and fallacy of restorative nostalgia. Nostalgia, I will illustrate, was a way for Xu Xu to give expression both to a real sense of loss as well as a sense of metaphysical homelessness that did not directly result from his exile in Hong Kong, but that is bound up with the experience of modernity and the reality of China’s cultural post-war politics. Nostalgia thus becomes the expression of a literary aesthetic that connects Xu Xu to a number of other writers who are typically associated with a twentieth-century revival of romanticism, foremost Hermann Hesse (1877−1962). Like for Xu Xu, the expression of nostalgia was as much an aesthetic gesture for Hesse as it was a political gesture. My reading of Xu Xu’s use of nostalgia thus challenges conventional interpretations of the use of nostalgia in postwar Chinese literature and enhances our understanding of the interplay of aesthetics and politics in the work of Chinese writers in exile. In my analysis of Xu’s work in the context of neo-romanticism, I will draw on the work of Michael Löwy who understands the romantic critique of modernity as bound up with an experience of loss. “The Romantic vision,” Löwy writes, “is characterized by the painful and melancholic conviction that in the modern reality something precious has been lost, at the level of both individuals and humanity at large; certain essential human values have been alienated. This alienation, keenly sensed, is often experienced as exile […]” (Löwy 2001, 21). Löwy quotes Friedrich Schlegel as speaking of the soul, the seat of humanness, as living “under the willows of exile (unter den Trauerweiden der Verbannung),” far removed from the true hearth of homeland (Löwy 2001, 21). It is precisely this sense of metaphysical homelessness, I will argue, that lies at the root of the nostalgic longing expressed by Xu Xu’s fictional protagonists. Yet Löwy’s study on romanticism informs this paper in another way. Löwy understands romanticism as a highly diverse movement the numerous strands of which can be found in genres and literatures not usually thought to be part of the romantic canon. By drawing on Xu’s own critical writing on the role of the artist in society and by illustrating his intellectual proximity to writers and thinkers of the romantic movement, I will argue that Xu Xu’s postwar fiction contributes to a transnational romantic canon and constitutes a creative engagement with romantic aesthetics that links modern Chinese literature to global literary modernity

Towards an Anomaly-Free Quantum Dynamics for a Weak Coupling Limit of Euclidean Gravity: Diffeomorphism Covariance

The G-->0 limit of Euclidean gravity introduced by Smolin is described by a generally covariant U(1)xU(1)xU(1) gauge theory. In an earlier paper, Tomlin and Varadarajan constructed the quantum Hamiltonian constraint of density weight 4/3 for this U(1)xU(1)xU(1) theory so as to produce a non-trivial anomaly free LQG-type representation of the Poisson bracket between a pair of Hamiltonian constraints. These constructions involved a choice of regulating coordinate patches. The use of these coordinate patches is in apparent conflict with spatial diffeomorphism covariance. In this work we show how an appropriate choice of coordinate patches together with suitable modifications of these constructions results in the diffeomorphism covariance of the continuum limit action of the Hamiltonian constraint operator, while preserving the anomaly free property of the continuum limit action of its commutator.Comment: 56 pages, No figure

N=1 Matter from Fractional Branes

We study a bound state of fractional D3-branes localized inside the world-volume of fractional D7-branes on the orbifold C^3/Z_2 x Z_2. We determine the open string spectrum that leads to N=1 U(N1)xU(N2)xU(N3)xU(N4) gauge theory with matter having the number of D7-branes as a flavor index. We derive the linearized boundary action of the D7-brane on this orbifold using the boundary state formalism and we discuss the tadpole cancellation. After computing the asymptotic expression of the supergravity solution the anomalies of the gauge theory are reproduced.Comment: LaTeX 20 pages, 1 figure, small changes and references adde