93 research outputs found
Solving the Conformal Constraints for Scalar Operators in Momentum Space and the Evaluation of Feynman's Master Integrals
No full textGraviton vertices and the mapping of anomalouscorrelators to momentum space for a generalconformal field theory
No full textWe investigate the mapping of conformal correlators and of their anomalies from configuration to momen- tum space for general dimensions, focusing on the anomalous correlators TOO, TVV - involving the energy- momentum tensor (T ) with a vector (V ) or a scalar operator (O) - and the 3-graviton vertex T T T . We compute the T OO, T V V and T T T one-loop vertex functions in dimensional regularization for free field theories involving conformal scalar, fermion and vector fields. Since there are only one or two independent tensor structures solv- ing all the conformal Ward identities for the T OO or T V V vertex functions respectively, and three independent tensor structures for the T T T vertex, and the coefficients of these tensors are known for free fields, it is possible to identify the corresponding tensors in momentum space from the computation of the correlators for free fields. This works in general d dimensions for T OO and T V V correlators, but only in 4 dimensions for T T T , since vector fields are conformal only in d = 4. In this way the general solution of the Ward identities including anomalous ones for these correlators in (Euclidean) position space, found by Osborn and Petkou is mapped to the ordinary diagrammatic one in momentum space. We give simplified expressions of all these correlators in configuration space which are explicitly Fourier integrable and provide a diagrammatic interpretation of all the contact terms arising when two or more of the points coincide. We discuss how the anomalies arise in each approach. We then outline a general algorithm for mapping correlators from position to momentum space, and illustrate its application in the case of the V V V and T OO vertices. The method implements an intermediate regularization - similar to differential regularization - for the identification of the integrands in momentum space, and one extra regulator. The relation between the ordinary Feynman expansion and the logarithmic one generated by this approach are briefly discussed
TTT in CFT: Trace identities and the conformal anomaly effective action
No full textStress-energy correlation functions in a general Conformal Field Theory (CFT) in four dimensions are described in a fully covariant approach, as metric variations of the quantum effective action in an arbitrary curved space background field. All Conservation, Trace and Conformal Ward Identities (CWIs), including contact terms, are completely fixed in this covariant approach. The Trace and CWIs are anomalous. Their anomalous contributions may be computed unambiguously by metric variation of the exact 1PI quantum effective action determined by the conformal anomaly of 〈Tμν〉 in d=4 curved space. This action implies the existence of massless propagator poles in three and higher point correlators of Tμν. The metric variations of the anomaly effective action in its local form in terms of a scalar conformalon field are carried out explicitly for the case of the correlator of three CFT stress-energy tensors, and the result is shown to coincide with the algebraic reconstruction of 〈TTT〉 from its transverse, tracefree parts, determined independently by the solution of the CWIs in d dimensional flat space in the momentum representation. This demonstrates that the specific analytic structure and massless poles predicted by the general curved space anomaly effective action are in fact a necessary feature of the exact solution of the anomalous CWIs in any d=4 CFT
Supporting Cyber-Physical Systems with Wireless Sensor Networks: An Outlook of Software and Services
No full textSensing, communication, computation and control technologies are the essential building blocks of a cyber-physical system (CPS). Wireless sensor networks (WSNs) are a way to support CPS as they provide fine-grained spatial-temporal sensing, communication and computation at a low premium of cost and power. In this article, we explore the fundamental concepts guiding the design and implementation of WSNs. We report the latest developments in WSN software and services for meeting existing requirements and newer demands; particularly in the areas of: operating system, simulator and emulator, programming abstraction, virtualization, IP-based communication and security, time and location, and network monitoring and management. We also reflect on the ongoing
efforts in providing dependable assurances for WSN-driven CPS. Finally, we report on its applicability with a case-study on smart buildings
The Trace Anomaly and Dynamical Vacuum Energy in Cosmology
No full textThe trace anomaly of conformal matter implies the existence of massless scalar poles in physical amplitudes involving the stress-energy tensor. These poles may be described by a local effective action with massless scalar fields, which couple to classical sources, contribute to gravitational scattering processes, and can have long range gravitational effects at macroscopic scales. In an effective field theory approach, the effective action of the anomaly is an infrared relevant term that should be added to the Einstein-Hilbert action of classical General Relativity to take account of macroscopic quantum effects. The additional scalar degrees of freedom contained in this effective action may be understood as responsible for both the Casimir effect in flat spacetime and large quantum backreaction effects at the horizon scale of cosmological spacetimes. These effects of the trace anomaly imply that the cosmological vacuum energy is dynamical, and its value depends on macroscopic boundary conditions at the cosmological horizon scale, rather than sensitivity to the extreme ultraviolet Planck scale.The trace anomaly of conformal matter implies the existence of massless scalar poles in physical amplitudes involving the stress-energy tensor. These poles may be described by a local effective action with massless scalar fields, which couple to classical sources, contribute to gravitational scattering processes, and can have long range gravitational effects at macroscopic scales. In an effective field theory approach, the effective action of the anomaly is an infrared relevant term that should be added to the Einstein-Hilbert action of classical General Relativity to take account of macroscopic quantum effects. The additional scalar degrees of freedom contained in this effective action may be understood as responsible for both the Casimir effect in flat spacetime and large quantum backreaction effects at the horizon scale of cosmological spacetimes. These effects of the trace anomaly imply that the cosmological vacuum energy is dynamical, and its value depends on macroscopic boundary conditions at the cosmological horizon scale, rather than sensitivity to the extreme ultraviolet Planck scale.The trace anomaly of conformal matter implies the existence of massless scalar poles in physical amplitudes involving the stress-energy tensor. These poles may be described by a local effective action with massless scalar fields, which couple to classical sources, contribute to gravitational scattering processes, and can have long range gravitational effects at macroscopic scales. In an effective field theory approach, the effective action of the anomaly is an infrared relevant term that should be added to the Einstein-Hilbert action of classical General Relativity to take account of macroscopic quantum effects. The additional scalar degrees of freedom contained in this effective action may be understood as responsible for both the Casimir effect in flat spacetime and large quantum backreaction effects at the horizon scale of cosmological spacetimes. These effects of the trace anomaly imply that the cosmological vacuum energy is dynamical, and its value depends on macroscopic boundary conditions at the cosmological horizon scale, rather than sensitivity to the extreme ultraviolet Planck scale
RF Information Harvesting for Medium Access in Event-driven Batteryless Sensing
No full textWe present radio-frequency (RF) information harvesting, a chan-nel sensing technique that takes advantage of the energy in the wireless medium to detect channel activity at essentially no en-ergy cost. RF information harvesting is essential for event-driven wireless sensing applications using battery-less devices that har-vest tiny amounts of energy from impromptu events, such as op-erating a switch, and then transmit the event notification to a one-hop gateway. As multiple such devices may concurrently de-tect events, coordinating access to the channel is key. RF infor-mation harvesting allows devices to break the symmetry between concurrently-transmitting devices based on the harvested energy from the ongoing transmissions. To demonstrate the benefits of RF information harvesting, we integrate it in a tailor-made ultra low-power hardware MAC protocol we call Radio Frequency-Distance Packet Queuing (RF-DiPaQ). We build a hardware/software proto-type of RF-DiPaQ and use an established Markov framework to study its performance at scale. Comparing RF-DiPaQ against sta-ple contention-based MAC protocols, we show that it outperforms pure Aloha and 1-CSMA by factors of 3.55 and 1.21 respectively in throughput, while it saturates at more than double the offered load compared to 1-CSMA. As traffic increases, the energy saving of RF-DiPaQ against CSMA protocols increases, consuming 36% less energy than np-CSMA at typical offered loads.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Embedded System
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Pair production and back reaction in strong fields: Numerical results
No full textThe problem I shall address in detail in this talk is pair production of either bosons or fermions from strong electric fields which are functions only of time t, or only of the fluid proper time {tau} = (t{sup 2} - z{sup 2}){sup 1/2}. I shall compare the results of the numerical simulation of this problem (for the degradation of the field, the particle spectra, etc.) with a semi-classical transport approach using a Schwinger-inspired source term
New Horizons in Gravity: The Trace Anomaly, Dark Energy and Condensate Stars
No full textGeneral Relativity receives quantum corrections relevant at macroscopic distance scales and near event horizons. These arise from the conformal scalar degrees of freedom in the extended effective field theory of gravity generated by the trace anomaly of massless quantum fields in curved space. The origin of these conformal scalar degrees of freedom as massless poles in two-particle intermediate states of anomalous amplitudes in flat space is exposed. At event horizons the conformal anomaly scalar degrees of freedom can have macroscopically large effects on the geometry, potentially removing the classical event horizon of black hole and cosmological spacetimes, replacing them with a quantum boundary layer where the effective value of the gravitational vacuum energy density can change. In the effective theory, the cosmological term becomes a dynamical condensate, whose value depends upon boundary conditions near the horizon. In the conformal phase where the anomaly induced fluctutations dominate, and the condensate dissolves, the effective cosmological "constant" is a running coupling which has an infrared stable fixed point at zero. By taking a positive value in the interior of a fully collapsed star, the effective cosmological term removes any singularity, replacing it with a smooth dark energy interior. The resulting gravitational condensate star configuration resolves all black hole paradoxes, and provides a testable alternat ive to black holes as the final state of complete gravitational collapse. The observed dark energy of our universe likewise may be a macroscopic finite size effect whose value depends not on microphysics but on the cosmological horizon scale.General Relativity receives quantum corrections relevant at macroscopic distance scales and near event horizons. These arise from the conformal scalar degrees of freedom in the extended effective field theory of gravity generated by the trace anomaly of massless quantum fields in curved space. The origin of these conformal scalar degrees of freedom as massless poles in two-particle intermediate states of anomalous amplitudes in flat space is exposed. At event horizons the conformal anomaly scalar degrees of freedom can have macroscopically large effects on the geometry, potentially removing the classical event horizon of black hole and cosmological spacetimes, replacing them with a quantum boundary layer where the effective value of the gravitational vacuum energy density can change. In the effective theory, the cosmological term becomes a dynamical condensate, whose value depends upon boundary conditions near the horizon. In the conformal phase where the anomaly induced fluctutations dominate, and the condensate dissolves, the effective cosmological 'constant' is a running coupling which has an infrared stable fixed point at zero. By taking a positive value in the interior of a fully collapsed star, the effective cosmological term removes any singularity, replacing it with a smooth dark energy interior. The resulting gravitational condensate star configuration resolves all black hole paradoxes, and provides a testable alternative to black holes as the final state of complete gravitational collapse. The observed dark energy of our universe likewise may be a macroscopic finite size effect whose value depends not on microphysics but on the cosmological horizon scale
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