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 of general relativity, which simply require that the vacuum energy 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 without a distinctively separate reheating phase,[5] thus providing a solution to the graceful exit problem of inflation.[1][2][6][7][8]
^ abLinde, A.D. (1982). "A new inflationary universe scenario: A possible solution of the horizon, flatness, homogeneity, isotropy and primordial monopole problems". Physics Letters B. 108 (6). Elsevier BV: 389–393. Bibcode:1982PhLB..108..389L. doi:10.1016/0370-2693(82)91219-9. ISSN0370-2693.
^Albrecht, Andreas; Steinhardt, Paul J. (26 April 1982). "Cosmology for Grand Unified Theories with Radiatively Induced Symmetry Breaking". Physical Review Letters. 48 (17). American Physical Society (APS): 1220–1223. Bibcode:1982PhRvL..48.1220A. doi:10.1103/physrevlett.48.1220. ISSN0031-9007.
^Albrecht, Andreas; Steinhardt, Paul J.; Turner, Michael S.; Wilczek, Frank (17 May 1982). "Reheating an Inflationary Universe". Physical Review Letters. 48 (20). American Physical Society (APS): 1437–1440. Bibcode:1982PhRvL..48.1437A. doi:10.1103/physrevlett.48.1437. ISSN0031-9007.