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The generator of spatial di eomorphisms in the Koslowski-Sahlmann representation
http://hdl.handle.net/2289/5862
Title: The generator of spatial di eomorphisms in the Koslowski-Sahlmann representation<br/><br/>Authors: Varadarajan, Madhavan<br/><br/>Abstract: A generalization of the representation, underlying the discrete spatial geometry of loop quantum gravity, to accomodate states labelled by smooth spatial geometries, was discovered by Koslowski and further studied by Sahlmann. We show how to construct the diffeomorphism constraint operator in this Koslowski–Sahlmann (KS) representation from suitable connection and triad dependent operators. We show that the KS representation supports the action of hitherto unnoticed 'background exponential' operators which, in contrast to the holonomy-flux operators, change the smooth spatial geometry label of the states. These operators are shown to be quantizations of certain connection dependent functions and play a key role in the construction of the diffeomorphism constraint operator.<br/><br/>Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Constraint algebra in loop quantum gravity reloaded. I. Toy model of a U(1)3 gauge theory
http://hdl.handle.net/2289/5861
Title: Constraint algebra in loop quantum gravity reloaded. I. Toy model of a U(1)3 gauge theory<br/><br/>Authors: Henderson, Adam; Laddha, Alok; Tomlin, Casey<br/><br/>Abstract: We analyze the issue of anomaly-free representations of the constraint algebra in loop quantum gravity (LQG) in the context of a diffeomorphism-invariant U(1)3 theory in three spacetime dimensions. We construct a Hamiltonian constraint operator whose commutator matches with a quantization of the classical Poisson bracket involving structure functions. Our quantization scheme is based on a geometric interpretation of the Hamiltonian constraint as a generator of phase space-dependent diffeomorphisms. The resulting Hamiltonian constraint at finite triangulation has a conceptual similarity with the μ¯ scheme in loop quantum cosmology and highly intricate action on the spin-network states of the theory. We construct a subspace of non-normalizable states (distributions) on which the continuum Hamiltonian constraint is defined which leads to an anomaly-free representation of the Poisson bracket of two Hamiltonian constraints in loop quantized framework. Our work, along with the work done in [C. Tomlin and M. Varadarajan, Phys. Rev. D 87, 044039 (2013)], suggests a new approach to the construction of anomaly-free quantum dynamics in Euclidean LQG.<br/><br/>Description: Open AccessEnhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light
http://hdl.handle.net/2289/5849
Title: Enhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light<br/><br/>Authors: Aasi, J.; Abadie, J.; Iyer, B.R.; and 150 co-authors<br/><br/>Abstract: Nearly a century after Einstein first predicted the existence of gravitational waves, a global network of Earth-based gravitational wave observatories1, 2, 3, 4 is seeking to directly detect this faint radiation using precision laser interferometry. Photon shot noise, due to the quantum nature of light, imposes a fundamental limit on the attometre-level sensitivity of the kilometre-scale Michelson interferometers deployed for this task. Here, we inject squeezed states to improve the performance of one of the detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) beyond the quantum noise limit, most notably in the frequency region down to 150 Hz, critically important for several astrophysical sources, with no deterioration of performance observed at any frequency. With the injection of squeezed states, this LIGO detector demonstrated the best broadband sensitivity to gravitational waves ever achieved, with important implications for observing the gravitational-wave Universe with unprecedented sensitivity<br/><br/>Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Condensation and intermittency in an open boundary aggregation-fragmentation model.
http://hdl.handle.net/2289/5844
Title: Condensation and intermittency in an open boundary aggregation-fragmentation model.<br/><br/>Authors: Sachdeva, Himani; Barma, Mustansir; Rao, Madan<br/><br/>Abstract: We study real space condensation in aggregation-fragmentation models where the total mass is not conserved, as in phenomena such as cloud formation and intracellular trafficking. We study the scaling properties of the system with influx and outflux of mass at the boundaries using numerical simulations, supplemented by analytical results in the absence of fragmentation. The system is found to undergo a phase transition to an unusual condensate phase, characterized by strong intermittency and giant fluctuations of the total mass. A related phase transition also occurs for biased movement of large masses, but with some crucial differences which we highlight.<br/><br/>Description: Open Access