Vacuum polarization by topological defects in de Sitter spacetime

In this paper we investigate the vacuum polarization effects associated with a massive quantum scalar field in de Sitter spacetime in the presence of gravitational topological defects. Specifically we calculate the vacuum expectation value of the field square, $$. Because this investigation has been developed in a pure de Sitter space, here we are mainly interested on the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and Quantum Gravity (MCCQG

Mesoscopic Transport Through Ballistic Cavities: A Random S-Matrix Theory Approach

We deduce the effects of quantum interference on the conductance of chaotic cavities by using a statistical ansatz for the S matrix. Assuming that the circular ensembles describe the S matrix of a chaotic cavity, we find that the conductance fluctuation and weak-localization magnitudes are universal: they are independent of the size and shape of the cavity if the number of incoming modes, N, is large. The limit of small N is more relevant experimentally; here we calculate the full distribution of the conductance and find striking differences as N changes or a magnetic field is applied.Comment: 4 pages revtex 3.0 (2-column) plus 2 postscript figures (appended), hub.pam.94.

Matrix Model Maps and Reconstruction of AdS SUGRA Interactions

We consider the question of reconstructing (cubic) SUGRA interactions in AdS/CFT. The method we introduce is based on the matrix model maps (MMP) which were previously successfully employed at the linearized level. The strategy is to start with the map for 1/2 BPS configurations which is exactly known (to all orders) in the hamiltonian framework. We then use the extension of the matrix model map with the corresponding Ward identities to completely specify the interaction. A central point in this construction is the non-vanishing of off-shell interactions (even for highest-weight states).Comment: 28 page

Margins, Liquidity and the Cost of Hedging

http://web.mit.edu/ceepr/www/publications/workingpapers.htmlRecent financial reforms, such as the Dodd-Frank Act in the U.S. and the European Market Infrastructure Regulation, encourage greater use of clearing and therefore increased margining of derivative trades. They also impose margining requirements on OTC derivative dealers. One question arising out of the debates over these reforms is, does a margin mandate increases the cost of hedging by non-financial corporations—the so-called end-users of derivatives? Our answer is, No. We show that a non-margined derivative is equivalent to a package of (i) a margined derivative, and (ii) a contingent line of credit. A margin mandate merely requires that this package be marketed as two distinct products, but it does not change the total financing or capital that the non-financial corporation requires to back its hedging. Nor does it raise the cost to banks or other dealer of offering the package, at least not directly. There may be an indirect effect if the clearing mandate succeeds in lowering systemic risk, but indirect macro effects such as this are beyond the scope of this paper. We also explore how accounting rules and bank regulations may treat the implicit credit embedded in the non-margined derivative differently from an explicit line of credit. This is important to understanding business and banker reaction to details of the proposal. Finally, we place the current debate in the context of the historical evolution of margin practices and regulations from the earliest trading of derivatives in the U.S. in the 1860’s to the present

Vacuum Polarization for a Massless Spin-1/2 Field in the Global Monopole Spacetime at Nonzero Temperature

In this paper we present the effects produced by the temperature in the renormalized vacuum expectation value of the zero-zero component of the energy-momentum tensor associated with massless left-handed spinor field in the pointlike global monopole spacetime. In order to develop this calculation we had to obtain the Euclidean thermal Green function in this background. Because the expression obtained for the thermal energy density cannot be expressed in a closed form, its explicit dependence on the temperature is not completely evident. So, in order to obtain concrete information about its thermal behavior, we develop a numerical analysis of our result in the high-temperature limit for specific values of the parameter $\alpha$ which codify the presence of the monopole.Comment: 22 pages, LaTex format, 5 figure