Gravitational form factor constraints and their universality
Peter Lowdon, Sabrina Cotogno, Cédric Lorcé
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6 pages. Talk presented at Light Cone 2019 - QCD on the light cone: from hadrons to heavy ions (LC2019), Ecole Polytechnique, Palaiseau, France, September 2019
By adopting a local QFT framework one can derive in a non-perturbative manner the constraints imposed by Poincaré symmetry on the form factors appearing in the Lorentz covariant decomposition of the energy-momentum tensor matrix elements. In particular, this approach enables one to prove that these constraints are in fact independent of the internal properties of the states appearing in the matrix elements. Here we outline the rationale behind this approach, and report on some of the implications of these findings.
We demonstrate the universality of the gravitational classical deflection angle of massless particles through O(G^3) by studying the high-energy limit of full two-loop four-graviton scattering amplitudes in pure Einstein gravity as well as N >= 4 supergravity. As a by-product, our first-principles calculation provides a direct confirmation of the massless deflection angle in Einstein gravity proposed long ago by Amati, Ciafaloni and Veneziano, and is inconsistent with a recently proposed alternative.
Relativistic spin states are convention dependent. In this work we prove that the zero momentum-transfer limits of the leading two form factors in the decomposition of the energy-momentum tensor matrix elements are independent of this choice. In particular, we demonstrate that these constraints are insensitive to whether the corresponding states are massive or not, and that they arise purely due to the Poincaré covariance of the states.
We provide a simple and clear verification of the physical need for temperature gradients in equilibrium states when gravitational fields are present. Our argument will be built in a completely kinematic manner, in terms of the gravitational red-shift/blue-shift of light, together with a relativistic extension of Maxwell's two column argument. We conclude by showing that it is the universality of the gravitational interaction (the uniqueness of free-fall) that ultimately permits Tolman's equilibrium temperature gradients without any violation of the laws of thermodynamics.
Universality of Primordial Anisotropies in Gravitational Wave Background
School of Physics Science and Engineering, Tongji University(同济大学物理科学与工程学院);Graduate School of Science and Engineering, Yamaguchi University(山口大学理工学研究科);Kavli Institute for the Physics and Mathematics of the Universe (WPI), UTIAS, The University of Tokyo(东京大学宇宙线研究所 Kavli宇宙物理数学研究所);Institute for Advanced Study of Tongji University(同济大学高等研究院);Center for Gravitation and Cosmology, Yangzhou University(扬州大学引力与宇宙学中心)
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