[Paper Review] Probing Models of Quantum Decoherence in Particle Physics and Cosmology

Nick E. Mavromatos, Sarben Sarkar|ArXiv.org|Dec 15, 2006

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper investigates quantum gravity-induced decoherence as a source of fundamental CPT violation, proposing that open quantum systems in foamy spacetime lead to non-unitary evolution and ill-defined CPT operators. It demonstrates that precision tests using neutral kaons and neutrinos—especially at upgraded φ-factories—can probe these effects, with potential signals detectable at current experimental sensitivities.

ABSTRACT

In this review we first discuss the string theoretical motivations for induced decoherence and deviations from ordinary quantum-mechanical behaviour; this leads to intrinsic CPT violation in the context of an extended class of quantum-gravity models. We then proceed to a description ofprecision tests of CPT symmetry and quantum mechanics using mainly neutral kaons and neutrinos. We also emphasize the possibly unique role of neutral meson factories in providing specific tests of models where the quantum-mechanical CPT operator is not well-defined, leading to modifications of Einstein-Podolsky-Rosen particle correlators. Finally, we discuss experimental probes of decoherence in a cosmological context, including studies of dissipative relaxation models of dark energy in the context of non-critical (non-equilibrium) string theory and the associated modifications of the Boltzmann equation for the evolution of species abundances.

Motivation & Objective

• To explore theoretical motivations for quantum gravity-induced decoherence from string theory and non-critical string models.
• To investigate how decoherence in quantum-gravitational environments leads to fundamental CPT violation, particularly through loss of unitarity and ill-defined CPT operators.
• To identify precision experimental probes—especially in neutral meson systems—capable of testing models where the CPT operator is not well-defined.
• To assess the impact of decoherence on cosmological observables, including relic abundances and dark energy dynamics in non-critical string cosmology.
• To evaluate the feasibility of detecting these quantum gravity effects in existing and upcoming experiments, such as upgraded φ-factories and neutrino oscillation facilities.

Proposed method

• Formalism of open quantum systems is applied to model low-energy effective field theories interacting with quantum-gravitational environments, leading to density matrix evolution via a modified Liouville equation.
• The Liouville equation incorporates a non-unitary correction term $\delta H\hskip-8.5pt/\hskip 2.0pt\rho$, representing decoherence from unobserved degrees of freedom trapped in spacetime foam.
• CPT violation is analyzed in the context of non-unitary evolution, where the scattering operator $\mathcal{S}$ fails to satisfy $\mathcal{S}\mathcal{S}^\dagger = \mathbb{I}$, leading to a breakdown of the standard CPT theorem.
• Einstein-Podolsky-Rosen (EPR) correlations are modified in models with ill-defined CPT operators, introducing observable $\omega$-like effects in entangled neutral meson systems.
• Cosmological models are extended using non-critical string theory, introducing time-dependent dilaton fields and graviton $\beta$-functions as sources in the Boltzmann equation for relic abundances.
• Relic density calculations are modified via a source term $\Gamma(t) = \dot{\Phi} - \frac{1}{2}e^{-\Phi}g^{\mu\nu}\tilde{\beta}_{\mu\nu}^{\rm Grav}$, altering freeze-out conditions and effective degrees of freedom $\tilde{g}_{\rm eff}$.

Experimental results

Research questions

• RQ1 Can quantum gravity-induced decoherence lead to observable CPT violation in low-energy effective field theories?
• RQ2 What are the measurable signatures of an ill-defined CPT operator in entangled neutral meson systems, such as those produced at φ-factories?
• RQ3 How do non-critical string cosmology models with time-dependent dilatons and gravitational $\beta$-functions modify the standard Boltzmann equation for relic abundances?
• RQ4 To what extent do decoherence effects in cosmology alter predictions for dark matter relic densities compared to standard thermal freeze-out?
• RQ5 Can current and near-future experiments on kaons and neutrinos falsify or constrain models of quantum gravity with induced decoherence?

Key findings

• Decoherence from quantum spacetime foam leads to non-unitary evolution, rendering the CPT operator ill-defined and resulting in a strong form of CPT violation.
• The modified Liouville equation $\partial_t \rho = i[\rho, H] + \delta H\hskip-8.5pt/\hskip 2.0pt\rho$ captures open quantum system dynamics in the presence of unobserved gravitational degrees of freedom.
• In φ-factory experiments, $\omega$-like effects on EPR correlations due to ill-defined CPT operators are predicted to be within reach of DA\Phi NE-2 upgrades.
• The relic density of dark matter is modified by a source term $\Gamma(t)$ involving time-dependent dilaton and graviton $\beta$-functions, altering the standard freeze-out condition.
• The modified freeze-out point $x_f^{-1}$ includes an integral over $\Gamma H^{-1}/x$, showing that both sign and magnitude of $\Gamma$ can increase or decrease relic abundances relative to the standard model.
• Constraints on supersymmetric dark matter models must be revisited in non-critical string cosmology, as decoherence effects can significantly alter relic density predictions.