Quantum Fluctuations in Cosmological Inflation
Summary
During the inflationary epoch the Universe underwent an exponential expansion driven by a scalar inflaton field. Quantum fluctuations of this field and of the metric were stretched beyond the Hubble radius and subsequently froze in, seeding the classical inhomogeneities observed in the cosmic microwave background and the large-scale distribution of matter. These fluctuations are typically treated in an effective field theory framework, in which slow-roll parameters control departures from exact de Sitter symmetry and determine the nearly scale-invariant power spectrum and small levels of non-Gaussianity. As modes cross the Hubble scale they become highly squeezed quantum states, and interactions with short-wavelength modes or an external environment can induce decoherence, thereby explaining the emergence of classical behaviour. Recent advances have explored the imprint of higher-order correlation functions, the role of mode coupling in generating entanglement entropy, and the mechanisms by which primordial tensor modes may decohere. Improved theoretical models are essential for interpreting precision measurements from upcoming experiments and for probing physics at energy scales far beyond those accessible on Earth.
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Quantum Fluctuations in Cosmological Inflation publication trend
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Technical terms
Inflaton: Hypothetical scalar field whose potential energy drives the accelerated expansion during inflation.
Quantum fluctuation: Temporary variation in a field or energy density arising from the uncertainty principle.
Hubble radius: Scale defined by the inverse Hubble parameter beyond which causal interactions cannot occur during inflation.
Decoherence: Process whereby quantum superpositions appear classical due to interactions with unobserved degrees of freedom.
Entanglement entropy: Quantitative measure of quantum correlations between different subsets of modes or fields.
Effective field theory: Framework that captures the low-energy dynamics of a system by integrating out high-energy degrees of freedom.
References
- Minimal decoherence from inflation. Journal of Cosmology and Astroparticle Physics (2023).
- Momentum-space entanglement entropy in de Sitter spacetime. Physical Review D (2023).
- Entanglement entropy of cosmological perturbations. Physical Review D (2020).
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