Arrow of Causality and Quantum Gravity.

Causality in quantum field theory is defined by the vanishing of field commutators for spacelike separations. However, this does not imply a direction for causal effects. Hidden in our conventions for quantization is a connection to the definition of an arrow of causality, i.e., what is the past and what is the future. If we mix quantization conventions within the same theory, we get a violation of microcausality. In such a theory with mixed conventions, the dominant definition of the arrow of causality is determined by the stable states. In some quantum gravity theories, such as quadratic gravity and possibly asymptotic safety, such a mixed causality condition occurs. We discuss some of the implications.

[1]  J. Donoghue,et al.  Gauge assisted quadratic gravity: A framework for UV complete quantum gravity , 2018, Physical Review D.

[2]  K. Stelle.  Renormalization of Higher Derivative Quantum Gravity , 1977 .

[3]  L. Rold,et al.  Vertex displacements for acausal particles: testing the Lee-Wick standard model at the LHC , 2009, 0908.2446.

[4]  Gabriel Menezes,et al.  Unitarity, stability, and loops of unstable ghosts , 2019, Physical Review D.

[5]  Danna Zhou,et al.  d. , 1840, Microbial pathogenesis.

[6]  T. D. Lee,et al.  Negative Metric and the Unitarity of the S Matrix , 1969 .

[7]  B. Grinstein,et al.  Causality as an emergent macroscopic phenomenon: The Lee-Wick O(N) model , 2008, 0805.2156.

[8]  P. Alam.  ‘L’ , 2021, Composites Engineering: An A–Z Guide.

[9]  M. Gell-Mann,et al.  Use of Causality Conditions in Quantum Theory , 1954 .

[10]  Thomas de Quincey.  [C] , 2000, The Works of Thomas De Quincey, Vol. 1: Writings, 1799–1820.

[11]  B. Holstein,et al.  Light-like scattering in quantum gravity , 2016, Journal of High Energy Physics.

[12]  Donoghue,et al.  General relativity as an effective field theory: The leading quantum corrections. , 1994, Physical review. D, Particles and fields.

[13]  M. Niedermaier,et al.  The Asymptotic Safety Scenario in Quantum Gravity , 2006, Living reviews in relativity.

[14]  A. Salvio.  Quadratic Gravity , 2018, Front. Phys..

[15]  Andrea M. Berlin.  A once and future king , 2015, Journal of Roman Archaeology.

[16]  Tsuyoshi Murata,et al.  {m , 1934, ACML.

[17]  Eugene P. Wigner,et al.  Lower Limit for the Energy Derivative of the Scattering Phase Shift , 1955 .