In
physical cosmology
Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of f ...
, warm inflation is one of two dynamical realizations of
cosmological inflation
In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from seconds after the conjectured Big Bang singularity ...
. The other is the standard scenario,
sometimes called cold inflation.
In warm inflation radiation production occurs concurrently with inflationary expansion. This is consistent with the conditions necessary for inflation as given by the
Friedmann equations
The Friedmann equations are a set of equations in physical cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity. They were first derived by Alexander Friedmann ...
of
general relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
, which simply require that the
vacuum energy
Vacuum energy is an underlying background energy that exists in space throughout the entire Universe. The vacuum energy is a special case of zero-point energy that relates to the quantum vacuum.
The effects of vacuum energy can be experimental ...
density dominates the energy content of the universe at time of inflation, and so does not prohibit some radiation to be present. As such the most general picture of inflation would include a radiation energy density component. The presence of radiation during inflation implies the inflationary phase could smoothly end into a
radiation-dominated era
The relative expansion of the universe is parametrized by a dimensionless scale factor a . Also known as the cosmic scale factor or sometimes the Robertson Walker scale factor, this is a key parameter of the Friedmann equations.
In the early st ...
without a distinctively separate reheating phase,
thus providing a solution to the
graceful exit problem of inflation.
References
{{Reflist
Particle physics
Inflation (cosmology)