According to inflation theory, the inflaton is a scalar field that is responsible for cosmic inflation in the very early universe. A quantized particle for this field is expected, similar to other quantum fields, called an inflaton. The field provides a mechanism by which a period of rapid expansion from 10−35 to 10−34 seconds after the initial expansion can be generated, forming the Universe.
The basic process of inflation consists of three steps:
- Prior to the expansion period, the inflaton field was at a higher-energy state.
- Random quantum fluctuations triggered a phase transition whereby the inflaton field released its potential energy as matter and radiation as it settled to its lowest-energy state.
- This action generated a repulsive force that drove the portion of the Universe that is observable to us today to expand from approximately 10−50 metres in radius at 10−35 seconds to almost 1 metre in radius at 10−34 seconds.
The inflaton field's lowest energy state may or may not be a zero energy state. This depends on the chosen potential energy density of the field.
The term inflaton was derived from inflation following the typical naming style of other quantum fields such as photon, gluon, boson and fermion. The term was first used in a paper entitled ‘After Primordial Inflation’ by, D.V. Nanopoulos, K.A. Olive and M. Srednicki 
- Metric expansion of space
- Hubble's law
- Big bang
- Cosmological constant
- Inflation (cosmology)
- Non-minimally coupled inflation
- Steinhardt, Paul J.; Turok, Neil (2007). Endless Universe: Beyond the Bang. Random House. p. 114. ISBN 978-0-7679-1501-4.
- Steinhardt, Paul J. (April 2011). "Inflation Debate: Is the theory at the heart of modern cosmology deeply flawed?". Scientific American.
- Nanopoulos, D.V., Olive, K.A., Srednicki, M. (July 1983) “After Primordial Inflation” Physics Letters
- Atkins, Michael (March 2012). "Could the Higgs Boson Be the Inflaton".
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