The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform

L. H. Ford - One of the best experts on this subject based on the ideXlab platform.

  • Vacuum Quantum Stress Tensor Fluctuations : A Diagonalization Approach
    Physical Review D, 2018
    Co-Authors: Enrico D. Schiappacasse, Christopher J. Fewster, L. H. Ford
    Abstract:

    Large vacuum fluctuations of a quantum Stress Tensor can be described by the asymptotic behavior of its probability distribution. Here we focus on Stress Tensor operators which have been averaged with a sampling function in time. The Minkowski vacuum state is not an eigenstate of the time-averaged operator, but can be expanded in terms of its eigenstates. We calculate the probability distribution and the cumulative probability distribution for obtaining a given value in a measurement of the time-averaged operator taken in the vacuum state. In these calculations, we use the normal ordered square of the time derivative of a massless scalar field in Minkowski spacetime as an example of a Stress Tensor operator. We analyze the rate of decrease of the tail of the probability distribution for different temporal sampling functions, such as compactly supported functions and the Lorentzian function. We find that the tails decrease relatively slowly, as exponentials of fractional powers, in agreement with previous work using the moments of the distribution. Our results lead additional support to the conclusion that large vacuum Stress Tensor fluctuations are more probable than large thermal fluctuations, and may have observable effects.

  • Quantum Stress Tensor Fluctuations and Primordial Gravity Waves
    Physical Review D, 2017
    Co-Authors: Jen-tsung Hsiang, L. H. Ford, Kin-wang Ng, Chun-hsien Wu
    Abstract:

    We examine the effect of the Stress Tensor of a quantum matter field, such as the electromagnetic field, on the spectrum of primordial gravity waves expected in inflationary cosmology. We find that the net effect is a small reduction in the power spectrum, especially at higher frequencies, but which has a different form from that described by the usual spectral index. Thus this effect has a characteristic signature, and is in principle observable. The net effect is a sum of two contributions, one of which is due to quantum fluctuations of the matter field Stress Tensor. The other is a quantum correction to the graviton field due to coupling to the expectation value of this Stress Tensor. Both contributions are sensitive to initial conditions in the very early universe, so this effect has the potential to act as a probe of these initial conditions.

  • Quantum Stress Tensor Fluctuations and their Physical Effects
    arXiv: General Relativity and Quantum Cosmology, 2008
    Co-Authors: L. H. Ford, Chun-hsien Wu
    Abstract:

    We summarize several aspects of recent work on quantum Stress Tensor fluctuations and their role in driving fluctuations of the gravitational field. The role of correlations and anticorrelations is emphasized. We begin with a review of the properties of the Stress Tensor correlation function. We next consider some illuminating examples of non‐gravitational effects of Stress Tensors fluctuations, specifically fluctuations of the Casimir force and radiation pressure fluctuations. We next discuss passive fluctuations of spacetime geometry and some of their operational signatures. These include luminosity fluctuations, line broadening, and angular blurring of a source viewed through a fluctuating gravitational field. Finally, we discuss the possible role of quantum Stress Tensor fluctuations in the early universe, especially in inflation. The fluctuations of the expansion of a congruence of comoving geodesics grows during the inflationary era, due to non‐cancellation of anticorrelations that would have occurr...

  • Minkowski vacuum Stress Tensor fluctuations
    Physical Review D, 2005
    Co-Authors: L. H. Ford, Thomas A. Roman
    Abstract:

    We study the fluctuations of the Stress Tensor for a massless scalar field in two- and four-dimensional Minkowski spacetime in the vacuum state. Covariant expressions for the Stress Tensor correlation function are obtained as sums of derivatives of a scalar function. These expressions allow one to express spacetime averages of the correlation function as finite integrals. We also study the correlation between measurements of the energy density along a world line. We find that these measurements may be either positively correlated or anticorrelated. The anticorrelated measurements can be interpreted as telling us that, if one measurement yields one sign for the averaged energy density, a successive measurement with a suitable time delay is likely to yield a result with the opposite sign.

  • Stress Tensor Fluctuations and Passive Quantum Gravity
    arXiv: General Relativity and Quantum Cosmology, 2001
    Co-Authors: L. H. Ford, Chun-hsien Wu
    Abstract:

    The quantum fluctuation of the Stress Tensor of a quantum field are discussed, as are the resulting spacetime metric fluctuations. Passive quantum gravity is an approximation in which gravity is not directly quantized, but fluctuations of the spacetime geometry are driven by Stress Tensor fluctuations. We discuss a decomposition of the Stress Tensor correlation function into three parts, and consider the physical implications of each part. The operational significance of metric fluctuations and the possible limits of validity of semiclassical gravity are discussed.

Francesco Pesavento - One of the best experts on this subject based on the ideXlab platform.

  • the solid phase Stress Tensor in porous media mechanics and the hill mandel condition
    Journal of The Mechanics and Physics of Solids, 2009
    Co-Authors: William G Gray, B A Schrefler, Francesco Pesavento
    Abstract:

    Abstract An assessment of the Stress Tensors used currently for the modeling of partially saturated porous media is made which includes concepts like total Stress, solid phase Stress, and solid pressure. Thermodynamically constrained averaging theory is used to derive the solid phase Stress Tensor. It is shown that in the upscaling procedure the Hill conditions are satisfied, which is not trivial. The Stress Tensor is then compared to traditional Stress measures. The physical meaning of two forms of solid pressure and of the Biot coefficient is clarified. Finally, a Bishop–Skempton like form of the Stress Tensor is obtained and a form of the total Stress Tensor that does not make use of the effective Stress concept.

  • The solid phase Stress Tensor in porous media mechanics and the Hill–Mandel condition
    Journal of The Mechanics and Physics of Solids, 2009
    Co-Authors: William G Gray, B A Schrefler, Francesco Pesavento
    Abstract:

    Abstract An assessment of the Stress Tensors used currently for the modeling of partially saturated porous media is made which includes concepts like total Stress, solid phase Stress, and solid pressure. Thermodynamically constrained averaging theory is used to derive the solid phase Stress Tensor. It is shown that in the upscaling procedure the Hill conditions are satisfied, which is not trivial. The Stress Tensor is then compared to traditional Stress measures. The physical meaning of two forms of solid pressure and of the Biot coefficient is clarified. Finally, a Bishop–Skempton like form of the Stress Tensor is obtained and a form of the total Stress Tensor that does not make use of the effective Stress concept.

William G Gray - One of the best experts on this subject based on the ideXlab platform.

  • the solid phase Stress Tensor in porous media mechanics and the hill mandel condition
    Journal of The Mechanics and Physics of Solids, 2009
    Co-Authors: William G Gray, B A Schrefler, Francesco Pesavento
    Abstract:

    Abstract An assessment of the Stress Tensors used currently for the modeling of partially saturated porous media is made which includes concepts like total Stress, solid phase Stress, and solid pressure. Thermodynamically constrained averaging theory is used to derive the solid phase Stress Tensor. It is shown that in the upscaling procedure the Hill conditions are satisfied, which is not trivial. The Stress Tensor is then compared to traditional Stress measures. The physical meaning of two forms of solid pressure and of the Biot coefficient is clarified. Finally, a Bishop–Skempton like form of the Stress Tensor is obtained and a form of the total Stress Tensor that does not make use of the effective Stress concept.

  • The solid phase Stress Tensor in porous media mechanics and the Hill–Mandel condition
    Journal of The Mechanics and Physics of Solids, 2009
    Co-Authors: William G Gray, B A Schrefler, Francesco Pesavento
    Abstract:

    Abstract An assessment of the Stress Tensors used currently for the modeling of partially saturated porous media is made which includes concepts like total Stress, solid phase Stress, and solid pressure. Thermodynamically constrained averaging theory is used to derive the solid phase Stress Tensor. It is shown that in the upscaling procedure the Hill conditions are satisfied, which is not trivial. The Stress Tensor is then compared to traditional Stress measures. The physical meaning of two forms of solid pressure and of the Biot coefficient is clarified. Finally, a Bishop–Skempton like form of the Stress Tensor is obtained and a form of the total Stress Tensor that does not make use of the effective Stress concept.

Chun-hsien Wu - One of the best experts on this subject based on the ideXlab platform.

  • Quantum Stress Tensor Fluctuations and Primordial Gravity Waves
    Physical Review D, 2017
    Co-Authors: Jen-tsung Hsiang, L. H. Ford, Kin-wang Ng, Chun-hsien Wu
    Abstract:

    We examine the effect of the Stress Tensor of a quantum matter field, such as the electromagnetic field, on the spectrum of primordial gravity waves expected in inflationary cosmology. We find that the net effect is a small reduction in the power spectrum, especially at higher frequencies, but which has a different form from that described by the usual spectral index. Thus this effect has a characteristic signature, and is in principle observable. The net effect is a sum of two contributions, one of which is due to quantum fluctuations of the matter field Stress Tensor. The other is a quantum correction to the graviton field due to coupling to the expectation value of this Stress Tensor. Both contributions are sensitive to initial conditions in the very early universe, so this effect has the potential to act as a probe of these initial conditions.

  • Quantum Stress Tensor Fluctuations and their Physical Effects
    arXiv: General Relativity and Quantum Cosmology, 2008
    Co-Authors: L. H. Ford, Chun-hsien Wu
    Abstract:

    We summarize several aspects of recent work on quantum Stress Tensor fluctuations and their role in driving fluctuations of the gravitational field. The role of correlations and anticorrelations is emphasized. We begin with a review of the properties of the Stress Tensor correlation function. We next consider some illuminating examples of non‐gravitational effects of Stress Tensors fluctuations, specifically fluctuations of the Casimir force and radiation pressure fluctuations. We next discuss passive fluctuations of spacetime geometry and some of their operational signatures. These include luminosity fluctuations, line broadening, and angular blurring of a source viewed through a fluctuating gravitational field. Finally, we discuss the possible role of quantum Stress Tensor fluctuations in the early universe, especially in inflation. The fluctuations of the expansion of a congruence of comoving geodesics grows during the inflationary era, due to non‐cancellation of anticorrelations that would have occurr...

  • Stress Tensor Fluctuations and Passive Quantum Gravity
    arXiv: General Relativity and Quantum Cosmology, 2001
    Co-Authors: L. H. Ford, Chun-hsien Wu
    Abstract:

    The quantum fluctuation of the Stress Tensor of a quantum field are discussed, as are the resulting spacetime metric fluctuations. Passive quantum gravity is an approximation in which gravity is not directly quantized, but fluctuations of the spacetime geometry are driven by Stress Tensor fluctuations. We discuss a decomposition of the Stress Tensor correlation function into three parts, and consider the physical implications of each part. The operational significance of metric fluctuations and the possible limits of validity of semiclassical gravity are discussed.

Tetsuo Hatsuda - One of the best experts on this subject based on the ideXlab platform.

  • distribution of Stress Tensor around static quark anti quark from yang mills gradient flow
    Physics Letters B, 2019
    Co-Authors: Ryosuke Yanagihara, Takumi Iritani, Masakiyo Kitazawa, Masayuki Asakawa, Tetsuo Hatsuda
    Abstract:

    Abstract The spatial distribution of the Stress Tensor around the quark–anti-quark ( Q Q ¯ ) pair in SU(3) lattice gauge theory is studied. The Yang–Mills gradient flow plays a crucial role to make the Stress Tensor well-defined and derivable from the numerical simulations on the lattice. The resultant Stress Tensor with a decomposition into local principal axes shows, for the first time, the detailed structure of the flux tube along the longitudinal and transverse directions in a gauge invariant manner. The linear confining behavior of the Q Q ¯ potential at long distances is derived directly from the integral of the local Stress Tensor.

  • Stress Tensor distribution in yang mills flux tube direct observation on the lattice with gradient flow
    2018
    Co-Authors: Ryosuke Yanagihara, Takumi Iritani, Masakiyo Kitazawa, Masayuki Asakawa, Tetsuo Hatsuda
    Abstract:

    The spatial distribution of the Stress Tensor around the quark--anti-quark ($Q\bar{Q}$) system in SU(3) lattice gauge theory is studied. The Yang-Mills gradient flow plays a crucial role to make the Stress Tensor well-defined and practically derivable from the numerical simulations on the lattice. Clear evidence of the flux tube formation and its transverse structure are presented from the Stress-Tensor distribution. The linear confining behavior of the $Q\bar{Q}$ potential at long distances is derived directly from the integral of the local Stress Tensor.