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Warm inflation may work with Standard Model physics alone

The early Universe’s inflationary expansion could be realized using known interactions of the Standard Model — without invoking any additional new physics. This is the conclusion of a new theoretical study published in Physical Review Letters, co-authored by Marco Drewes, Mercator Fellow of the SFB 1258.

Inflation — a period of extremely rapid expansion shortly after the Big Bang — is the leading explanation for the origin of the large-scale structure of the Universe. In the conventional picture, space expands extremely fast in a very cold vacuum. Such “cold” inflation often usually requires entirely new forces or the existence of hypothetical new elementary particles that are inaccessible to experiments. Warm inflation, proposed already in 1995, instead assumes that there is heat — a thermal bath — present during acceleration. Until now, theorists believed that warm inflation cannot be powered by the known forces of nature, because particles produced in the process would suppress the necessary conversion of inflaton energy into heat.

The model fits all cosmology data

The authors — among them Prof. Marco Drewes from the Université catholique de Louvain and Mercator Fellow of the Collaborative Research Center 1258 (SFB1258) at the Technical University of Munich — show that this suppression is naturally overcome by the expansion itself: the exponential growth of spacetime dilutes the disturbing particle effects so strongly that they no longer block warm inflation. This can be realized through a new particle coupled to gluons, the mediators of the strong force.

“What sets our model apart is that the heating mechanism uses one of the already known forces — the strong nuclear force and that we introduce only one new particle rather than many", Marco Drewes explains. This new particle also appears in axion theories, with axions being possible dark matter candidates that are currently being searched for in laboratories worldwide. "Therefore, this particle could actually be discovered with today’s technology — unlike in most competing scenarios,” Drewes adds.

Additionally, the model also naturally leads to a smooth transition from inflation to the subsequent phase in which the universe is filled with hot plasma that we see in the Cosmic Microwave Background, avoiding the need for additional new particles to explain that transition.

Original publication

Kim V. Berghaus, Marco Drewes, and Sebastian Zell:
Warm inflation with the Standard Model
Phys. Rev. Lett. 135, 171002, 23 October 2025
DOI: https://doi.org/10.1103/9nn9-bsm9

Contact

Prof. Dr. Marco Drewes
Université catholique de Louvain
Centre for Cosmology, Particle Physics and Phenomenology
Louvain, Belgium
and
Technical University of Munich
School of Natural Sciences
Collaborative Research Centre 1258
Garching, Germany
E-Mail: marco.drewes@tum.de

Further news

1] https://www.nature.com/articles/d41586-025-03414-9 

[2] https://www.scientificamerican.com/article/did-dark-matter-help-supersize-the-universe/ 

[3] https://phys.org/news/2025-10-universe-cosmic-inflation-standard-particle.html 

[4] https://www.spektrum.de/news/warme-inflation-lief-der-urknall-voellig-anders-ab-als-gedacht/2293397

Warm inflation may work with Standard Model physics alone

The early Universe’s inflationary expansion could be realized using known interactions of the Standard Model — without invoking any additional new physics. This is the conclusion of a new theoretical study published in Physical Review Letters, co-authored by Marco Drewes, Mercator Fellow of the SFB 1258.

Inflation — a period of extremely rapid expansion shortly after the Big Bang — is the leading explanation for the origin of the large-scale structure of the Universe. In the conventional picture, space expands extremely fast in a very cold vacuum. Such “cold” inflation often usually requires entirely new forces or the existence of hypothetical new elementary particles that are inaccessible to experiments. Warm inflation, proposed already in 1995, instead assumes that there is heat — a thermal bath — present during acceleration. Until now, theorists believed that warm inflation cannot be powered by the known forces of nature, because particles produced in the process would suppress the necessary conversion of inflaton energy into heat.

The model fits all cosmology data

The authors — among them Prof. Marco Drewes from the Université catholique de Louvain and Mercator Fellow of the Collaborative Research Center 1258 (SFB1258) at the Technical University of Munich — show that this suppression is naturally overcome by the expansion itself: the exponential growth of spacetime dilutes the disturbing particle effects so strongly that they no longer block warm inflation. This can be realized through a new particle coupled to gluons, the mediators of the strong force.

“What sets our model apart is that the heating mechanism uses one of the already known forces — the strong nuclear force and that we introduce only one new particle rather than many", Marco Drewes explains. This new particle also appears in axion theories, with axions being possible dark matter candidates that are currently being searched for in laboratories worldwide. "Therefore, this particle could actually be discovered with today’s technology — unlike in most competing scenarios,” Drewes adds.

Additionally, the model also naturally leads to a smooth transition from inflation to the subsequent phase in which the universe is filled with hot plasma that we see in the Cosmic Microwave Background, avoiding the need for additional new particles to explain that transition.

Original publication

Kim V. Berghaus, Marco Drewes, and Sebastian Zell:
Warm inflation with the Standard Model
Phys. Rev. Lett. 135, 171002, 23 October 2025
DOI: https://doi.org/10.1103/9nn9-bsm9

Contact

Prof. Dr. Marco Drewes
Université catholique de Louvain
Centre for Cosmology, Particle Physics and Phenomenology
Louvain, Belgium
and
Technical University of Munich
School of Natural Sciences
Collaborative Research Centre 1258
Garching, Germany
E-Mail: marco.drewes@tum.de

Further news

1] https://www.nature.com/articles/d41586-025-03414-9 

[2] https://www.scientificamerican.com/article/did-dark-matter-help-supersize-the-universe/ 

[3] https://phys.org/news/2025-10-universe-cosmic-inflation-standard-particle.html 

[4] https://www.spektrum.de/news/warme-inflation-lief-der-urknall-voellig-anders-ab-als-gedacht/2293397

News Items

Warm inflation may work with Standard Model physics alone

The early Universe’s inflationary expansion could be realized using known interactions of the Standard Model — without invoking any additional new physics. This is the conclusion of a new theoretical study published in Physical Review Letters, co-authored by Marco Drewes, Mercator Fellow of the SFB 1258.

Inflation — a period of extremely rapid expansion shortly after the Big Bang — is the leading explanation for the origin of the large-scale structure of the Universe. In the conventional picture, space expands extremely fast in a very cold vacuum. Such “cold” inflation often usually requires entirely new forces or the existence of hypothetical new elementary particles that are inaccessible to experiments. Warm inflation, proposed already in 1995, instead assumes that there is heat — a thermal bath — present during acceleration. Until now, theorists believed that warm inflation cannot be powered by the known forces of nature, because particles produced in the process would suppress the necessary conversion of inflaton energy into heat.

The model fits all cosmology data

The authors — among them Prof. Marco Drewes from the Université catholique de Louvain and Mercator Fellow of the Collaborative Research Center 1258 (SFB1258) at the Technical University of Munich — show that this suppression is naturally overcome by the expansion itself: the exponential growth of spacetime dilutes the disturbing particle effects so strongly that they no longer block warm inflation. This can be realized through a new particle coupled to gluons, the mediators of the strong force.

“What sets our model apart is that the heating mechanism uses one of the already known forces — the strong nuclear force and that we introduce only one new particle rather than many", Marco Drewes explains. This new particle also appears in axion theories, with axions being possible dark matter candidates that are currently being searched for in laboratories worldwide. "Therefore, this particle could actually be discovered with today’s technology — unlike in most competing scenarios,” Drewes adds.

Additionally, the model also naturally leads to a smooth transition from inflation to the subsequent phase in which the universe is filled with hot plasma that we see in the Cosmic Microwave Background, avoiding the need for additional new particles to explain that transition.

Original publication

Kim V. Berghaus, Marco Drewes, and Sebastian Zell:
Warm inflation with the Standard Model
Phys. Rev. Lett. 135, 171002, 23 October 2025
DOI: https://doi.org/10.1103/9nn9-bsm9

Contact

Prof. Dr. Marco Drewes
Université catholique de Louvain
Centre for Cosmology, Particle Physics and Phenomenology
Louvain, Belgium
and
Technical University of Munich
School of Natural Sciences
Collaborative Research Centre 1258
Garching, Germany
E-Mail: marco.drewes@tum.de

Further news

1] https://www.nature.com/articles/d41586-025-03414-9 

[2] https://www.scientificamerican.com/article/did-dark-matter-help-supersize-the-universe/ 

[3] https://phys.org/news/2025-10-universe-cosmic-inflation-standard-particle.html 

[4] https://www.spektrum.de/news/warme-inflation-lief-der-urknall-voellig-anders-ab-als-gedacht/2293397

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