warm inflation

{{Short description|Dynamical realization of cosmic inflation}}

In physical cosmology, warm inflation is one of two dynamical realizations of cosmological inflation. The other is the standard scenario,{{cite journal | last=Guth | first=Alan H. | title=Inflationary universe: A possible solution to the horizon and flatness problems | journal=Physical Review D | publisher=American Physical Society (APS) | volume=23 | issue=2 | date=15 January 1981 | issn=0556-2821 | doi=10.1103/physrevd.23.347 | pages=347–356| bibcode=1981PhRvD..23..347G |doi-access=free}}{{cite journal | last=Linde | first=A.D. | title=A new inflationary universe scenario: A possible solution of the horizon, flatness, homogeneity, isotropy and primordial monopole problems | journal=Physics Letters B | publisher=Elsevier BV | volume=108 | issue=6 | year=1982 | issn=0370-2693 | doi=10.1016/0370-2693(82)91219-9 | pages=389–393| bibcode=1982PhLB..108..389L }}{{cite journal | last1=Albrecht | first1=Andreas | last2=Steinhardt | first2=Paul J. | title=Cosmology for Grand Unified Theories with Radiatively Induced Symmetry Breaking | journal=Physical Review Letters | publisher=American Physical Society (APS) | volume=48 | issue=17 | date=26 April 1982 | issn=0031-9007 | doi=10.1103/physrevlett.48.1220 | pages=1220–1223| bibcode=1982PhRvL..48.1220A }} sometimes called cold inflation.{{cite journal | last=Berera | first=Arjun | title=Warm Inflation | journal=Physical Review Letters | volume=75 | issue=18 | date=30 October 1995 | issn=0031-9007 | doi=10.1103/physrevlett.75.3218| arxiv=astro-ph/9509049 | pages=3218–3221| pmid=10059529 | bibcode=1995PhRvL..75.3218B | s2cid=39966621 }}

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,{{cite journal | last=Berera | first=Arjun | title=Interpolating the stage of exponential expansion in the early universe: Possible alternative with no reheating | journal=Physical Review D | publisher=American Physical Society (APS) | volume=55 | issue=6 | date=15 March 1997 | issn=0556-2821 | doi=10.1103/physrevd.55.3346 | pages=3346–3357| arxiv=hep-ph/9612239 | bibcode=1997PhRvD..55.3346B | s2cid=2195582 }} thus providing a solution to the graceful exit problem of inflation.{{cite journal | last1=Albrecht | first1=Andreas | last2=Steinhardt | first2=Paul J. | last3=Turner | first3=Michael S. | last4=Wilczek | first4=Frank | title=Reheating an Inflationary Universe | journal=Physical Review Letters | publisher=American Physical Society (APS) | volume=48 | issue=20 | date=17 May 1982 | issn=0031-9007 | doi=10.1103/physrevlett.48.1437 | pages=1437–1440| bibcode=1982PhRvL..48.1437A }}{{cite journal | last1=Dolgov | first1=A.D. | last2=Linde | first2=A.D. | title=Baryon asymmetry in the inflationary universe | journal=Physics Letters B | publisher=Elsevier BV | volume=116 | issue=5 | year=1982 | issn=0370-2693 | doi=10.1016/0370-2693(82)90292-1 | pages=329–334| bibcode=1982PhLB..116..329D }}{{cite journal | last1=Abbott | first1=L.F. | last2=Farhi | first2=Edward | last3=Wise | first3=Mark B. | title=Particle production in the new inflationary cosmology | journal=Physics Letters B | publisher=Elsevier BV | volume=117 | issue=1–2 | year=1982 | issn=0370-2693 | doi=10.1016/0370-2693(82)90867-x | pages=29–33| bibcode=1982PhLB..117...29A | doi-access=free }}