The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform
Patrick Mcdonald - One of the best experts on this subject based on the ideXlab platform.
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distribution function approach to redshift space distortions
Journal of Cosmology and Astroparticle Physics, 2011Co-Authors: Uros Seljak, Patrick McdonaldAbstract:We develop a phase space distribution function approach to redshift space distortions (RSD), in which the redshift space density can be written as a sum over velocity moments of the distribution function. These moments are density weighted and have well defined physical interpretation: their lowest orders are density, momentum density, and stress energy density. The series expansion is convergent if kμu/aH < 1, where k is the waveVector, H the Hubble parameter, u the typical gravitational velocity and μ = cos θ, with θ being the angle between the Fourier mode and the line of sight. We perform an expansion of these velocity moments into helicity modes, which are eigenmodes under rotation around the axis of Fourier mode direction, generalizing the scalar, Vector, tensor decomposition of perturbations to an arbitrary order. We show that only equal helicity moments correlate and derive the angular dependence of the individual contributions to the redshift space power spectrum. We show that the dominant term of μ2 dependence on large scales is the cross-correlation between the density and scalar Part of momentum density, which can be related to the time derivative of the matter power spectrum. Additional terms contributing to μ2 and dominating on small scales are the Vector Part of momentum density-momentum density correlations, the energy density-density correlations, and the scalar Part of anisotropic stress density-density correlations. The second term is what is usually associated with the small scale Fingers-of-God damping and always suppresses power, but the first term comes with the opposite sign and always adds power. Similarly, we identify 7 terms contributing to μ4 dependence. Some of the advantages of the distribution function approach are that the series expansion converges on large scales and remains valid in multi-stream situations. We finish with a brief discussion of implications for RSD in galaxies relative to dark matter, highlighting the issue of scale dependent bias of velocity moments correlators.
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distribution function approach to redshift space distortions
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Uros Seljak, Patrick McdonaldAbstract:We develop a phase space distribution function approach to redshift space distortions (RSD), in which the redshift space density can be written as a sum over velocity moments of the distribution function. These moments are density weighted and their lowest orders are density, momentum density, and stress energy density. The series expansion is convergent on large scales. We perform an expansion of these velocity moments into helicity modes, which are eigenmodes under rotation around the axis of Fourier mode direction, generalizing the scalar, Vector, tensor decomposition of perturbations to an arbitrary order. We show that only equal helicity moments correlate and derive the angular dependence of the individual contributions to the redshift space power spectrum in terms of angle mu between wave Vector and line of sight. We show that the dominant term of mu^2 dependence on large scales is the cross-correlation between the density and scalar Part of momentum density, which can be related to the time derivative of the matter power spectrum. Additional terms contributing and dominating on small scales are the Vector Part of momentum density-momentum density correlations, the energy density-density correlations, and the scalar Part of anisotropic stress density-density correlations. Similarly, we identify 7 terms contributing to mu^4 dependence. Some of the advantages of the distribution function approach are that the series expansion converges on large scales and remains valid in multi-stream situations. We finish with a brief discussion of implications for RSD in galaxies relative to dark matter, highlighting the issue of scale dependent bias of velocity moments correlators.
J N Reddy - One of the best experts on this subject based on the ideXlab platform.
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A conformal gauge theory of solids: Insights into a class of electromechanical and magnetomechanical phenomena
Journal of The Mechanics and Physics of Solids, 2019Co-Authors: J N ReddyAbstract:Abstract A gauge theory of solids with conformal symmetry is formulated to model various electromechanical and magnetomechanical coupling phenomena. If the pulled back metric of the current configuration (the right Cauchy-Green tensor) is scaled with a constant, the volumetric Part of the Lagrange density changes while the isochoric Part remains invariant. However, upon a position dependent scaling, the isochoric Part also loses invariance. In order to restore the invariance of the isochoric Part, a 1-form compensating field is introduced and the notion of a gauge covariant derivative is utilized to minimally replace the Lagrangian. In view of obvious similarities with the Weyl geometry, the Weyl condition is imposed through the Lagrangian and a minimal coupling is employed so the 1-form could evolve. On deriving the Euler-Lagrange equations based on Hamilton's principle, we observe a close similarity with the governing equations for flexoelectricity under isochoric deformation if the exact Part of 1-form is interpreted as the electric field and the anti-exact Part as the polarization Vector. Next, we model piezoelectricity and electrostriction phenomena by contracting the Weyl condition in various ways. Applying the Hodge decomposition theorem on the 1-form which leads to the curl of a pseudo-Vector field and a Vector field, we also model magnetomechanical phenomena. Identifying the pseudo-Vector field with magnetic potential and the Vector Part with magnetization, flexomagnetism, piezomagnetism and magnetostriction phenomena under isochoric deformation are also modeled. Finally, we consider an analytical solution of the equations for piezoelectricity and propose a flexoelectric plate model to illustrate on the insightful information that the present approach potentially provides.
Uros Seljak - One of the best experts on this subject based on the ideXlab platform.
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distribution function approach to redshift space distortions
Journal of Cosmology and Astroparticle Physics, 2011Co-Authors: Uros Seljak, Patrick McdonaldAbstract:We develop a phase space distribution function approach to redshift space distortions (RSD), in which the redshift space density can be written as a sum over velocity moments of the distribution function. These moments are density weighted and have well defined physical interpretation: their lowest orders are density, momentum density, and stress energy density. The series expansion is convergent if kμu/aH < 1, where k is the waveVector, H the Hubble parameter, u the typical gravitational velocity and μ = cos θ, with θ being the angle between the Fourier mode and the line of sight. We perform an expansion of these velocity moments into helicity modes, which are eigenmodes under rotation around the axis of Fourier mode direction, generalizing the scalar, Vector, tensor decomposition of perturbations to an arbitrary order. We show that only equal helicity moments correlate and derive the angular dependence of the individual contributions to the redshift space power spectrum. We show that the dominant term of μ2 dependence on large scales is the cross-correlation between the density and scalar Part of momentum density, which can be related to the time derivative of the matter power spectrum. Additional terms contributing to μ2 and dominating on small scales are the Vector Part of momentum density-momentum density correlations, the energy density-density correlations, and the scalar Part of anisotropic stress density-density correlations. The second term is what is usually associated with the small scale Fingers-of-God damping and always suppresses power, but the first term comes with the opposite sign and always adds power. Similarly, we identify 7 terms contributing to μ4 dependence. Some of the advantages of the distribution function approach are that the series expansion converges on large scales and remains valid in multi-stream situations. We finish with a brief discussion of implications for RSD in galaxies relative to dark matter, highlighting the issue of scale dependent bias of velocity moments correlators.
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distribution function approach to redshift space distortions
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Uros Seljak, Patrick McdonaldAbstract:We develop a phase space distribution function approach to redshift space distortions (RSD), in which the redshift space density can be written as a sum over velocity moments of the distribution function. These moments are density weighted and their lowest orders are density, momentum density, and stress energy density. The series expansion is convergent on large scales. We perform an expansion of these velocity moments into helicity modes, which are eigenmodes under rotation around the axis of Fourier mode direction, generalizing the scalar, Vector, tensor decomposition of perturbations to an arbitrary order. We show that only equal helicity moments correlate and derive the angular dependence of the individual contributions to the redshift space power spectrum in terms of angle mu between wave Vector and line of sight. We show that the dominant term of mu^2 dependence on large scales is the cross-correlation between the density and scalar Part of momentum density, which can be related to the time derivative of the matter power spectrum. Additional terms contributing and dominating on small scales are the Vector Part of momentum density-momentum density correlations, the energy density-density correlations, and the scalar Part of anisotropic stress density-density correlations. Similarly, we identify 7 terms contributing to mu^4 dependence. Some of the advantages of the distribution function approach are that the series expansion converges on large scales and remains valid in multi-stream situations. We finish with a brief discussion of implications for RSD in galaxies relative to dark matter, highlighting the issue of scale dependent bias of velocity moments correlators.
Schwenk A. - One of the best experts on this subject based on the ideXlab platform.
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Coherent elastic neutrino-nucleus scattering: EFT analysis and nuclear responses
'American Physical Society (APS)', 2020Co-Authors: Hoferichter M., Menéndez J., Schwenk A.Abstract:The cross section for coherent elastic neutrino-nucleus scattering (CEνNS) depends on the response of the target nucleus to the external current, in the Standard Model (SM) mediated by the exchange of a Z boson. This is typically subsumed into an object called the weak form factor of the nucleus. Here, we provide results for this form factor calculated using the large-scale nuclear shell model for a wide range of nuclei of relevance for current CEνNS experiments, including cesium, iodine, argon, fluorine, sodium, germanium, and xenon. In addition, we provide the responses needed to capture the axial-Vector Part of the cross section, which does not scale coherently with the number of neutrons, but may become relevant for the SM prediction of CEνNS on target nuclei with nonzero spin. We then generalize the formalism allowing for contributions beyond the SM. In Particular, we stress that in this case, even for Vector and axial-Vector operators, the standard weak form factor does not apply anymore, but needs to be replaced by the appropriate combination of the underlying nuclear structure factors. We provide the corresponding expressions for Vector, axial-Vector, but also (pseudo)scalar, tensor, and dipole effective operators, including two-body-current effects as predicted from chiral effective field theory (EFT). Finally, we update the spin-dependent structure factors for dark matter scattering off nuclei according to our improved treatment of the axial-Vector responses
Schwenk Achim - One of the best experts on this subject based on the ideXlab platform.
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Coherent elastic neutrino-nucleus scattering: EFT analysis and nuclear responses
2020Co-Authors: Hoferichter Martin, Menéndez Javier, Schwenk AchimAbstract:The cross section for coherent elastic neutrino-nucleus scattering (CE$\nu$NS) depends on the response of the target nucleus to the external current, in the Standard Model (SM) mediated by the exchange of a $Z$ boson. This is typically subsumed into an object called the weak form factor of the nucleus. Here, we provide results for this form factor calculated using the large-scale nuclear shell model for a wide range of nuclei of relevance for current CE$\nu$NS experiments, including cesium, iodine, argon, fluorine, sodium, germanium, and xenon. In addition, we provide the responses needed to capture the axial-Vector Part of the cross section, which does not scale coherently with the number of neutrons, but may become relevant for the SM prediction of CE$\nu$NS on target nuclei with nonzero spin. We then generalize the formalism allowing for contributions beyond the SM. In Particular, we stress that in this case, even for Vector and axial-Vector operators, the standard weak form factor does not apply anymore, but needs to be replaced by the appropriate combination of the underlying nuclear structure factors. We provide the corresponding expressions for Vector, axial-Vector, but also (pseudo-)scalar, tensor, and dipole effective operators, including two-body-current effects as predicted from chiral effective field theory. Finally, we update the spin-dependent structure factors for dark matter scattering off nuclei according to our improved treatment of the axial-Vector responses.Comment: 28 pages, 11 figure
