# Quantum Field Theory & Gravity

Understanding discoveries at the Energy, Intensity, and Cosmic Frontiers

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## Quantum Field Theory and Gravity at Los Alamos

The HEP effort at Los Alamos in this area is actively pursing a number of questions in this area.

• What is the final state of complete gravitational collapse?
• What happens at the event horizon?
• What is dark energy?
• How did the universe begin? What is its large scale structure and evolution?
• How can gravity be unified with quantum mechanics and the Standard Model?
Quantum Field Theory, Gravity & Cosmology

There are two problems at the forefront of theoretical physics where quantum effects may play a decisive role in gravitational phenomena at macroscopic distance scales. The first is the problem of ultimate gravitational collapse, presumed in classical GR to lead a black hole singularity, which generates a number of paradoxes and challenges for quantum theory. The second is existence and magnitude of the cosmological dark energy, which is driving the accelerated expansion of the universe and which has the same equation of state as that of the quantum vacuum.

Gravitational Vacuum Condensate Stars

Mottola and external collaborator Mazur have proposed that the endpoint of gravitational collapse is a cold, non-singular, compact remnant, with a physical surface boundary layer of finite thickness, and with some quite different properties and astrophysical signatures than a classical black hole [ P. O. Mazur and E. Mottola, Proc. Nat. Acad. Sci. 101, 9545 (2004)]. These ideas were the subject of several articles in the popular press [Gravastars,'' New Scientist, Jan. 12, 2002, (cover story); Frozen Stars,'' {\it Scientific American}, July 7, 2003; the Santa Fe New Mexican], and recently a Letter in Physics Today .

Cosmology, Dark Energy and CMB Non-Gaussianity

Mottola and external collaborators (JCAP 1209 (2012) 024) have shown that in addition to simple scale invariance, a universe dominated by dark energy naturally gives rise to correlation functions possessing full conformal invariance. This gives rise to a characteristic conformal invariant perturbation spectrum and definite prediction for the shape of the non-Gaussian CMB bispectrum. The detection of non-Gaussian correlations in the CMB of one of these bispectral shape functions can both pinpoint the origin of primordial density fluctuations, and distinguish between different dynamical models of cosmological vacuum dark energy.

Macroscopic Effects of the Trace Anomaly, and the Quantum Effective Theory of Gravity

Mottola and external collaborators (Phys.Rev. D74 (2006) 064004, Acta Phys.Polon. B41 (2010) 2031-2162) have shown that classical 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 theory of gravity generated by the trace anomaly of quantum fields in curved space, which are not present in Einstein's classical theory. The effective action of the anomaly is an infrared relevant term that should be added to the Einstein-Hilbert action to take account of macroscopic quantum effects. This amounts to a well-defined modification of classical General Relativity fully consistent with, and in fact required by quantum theory, the Standard Model and the Equivalence Principle, without any additional assumptions.

Instability of de Sitter Space and the Cosmological Constant Problem

Mottola and external collaborators (New J.Phys. 9 (2007) 11, arXiv:1310.1963, arXiv:1310.0030) have shown that global de Sitter space is unstable to particle creation, even for a massive free field theory with no self-interactions. The Euclidean O(4,1) de Sitter invariant state usually assumed in inflation is a definite phase coherent superposition of particle and anti-particle solutions in both the asymptotic past and future, and therefore is not a true vacuum state. There are perturbations of this state with arbitrarily small energy density at early times that is exponentially blueshifted in the contracting phase of 'eternal' de Sitter space, and becomes large enough to disturb the classical geometry through the semiclassical Einstein equations at later times.

Conformal Field Theory Correlations of Energy-Momentum

Mottola and external collaborators (JHEP 1208 (2012) 147, JHEP 1307 (2013) 011) have investigated the structure of the constraints on three-point correlation functions of conformal invariance in momentum space and in arbitrary space-time dimensions relevant to massless anomaly poles and therefore the infrared macroscopic effects of the conformal trace anomaly in QFT in curved spacetime.

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