Compare · The Origin of Our Universe

Higgs Inflation vs New Inflation

Inflationary Big Bang · within family

	Higgs Inflation Strongly supported	New Inflation Historical
Proposed	2008	1982
Key figures	Fedor Bezrukov, Mikhail Shaposhnikov	Andrei Linde, Andreas Albrecht, Paul Steinhardt
In one sentence	Bezrukov and Shaposhnikov proposed in 2008 that the Standard Model Higgs field drove inflation, provided it couples strongly to the curvature of spacetime, using only the particles of the Standard Model.	Linde and independently Albrecht and Steinhardt replaced Old Inflation's bubble nucleation with a scalar field slowly rolling down a flat potential, producing a coherent end to inflation across whole Hubble regions and the first viable predictions for cosmological perturbations.
Predictions	In the [[cosmic microwave background]], a spectral index n_s near 0.97 and a tensor-to-scalar ratio r near 0.003, almost independent of Standard Model parameters when the Higgs mass sits well above its critical value A lower bound on the Higgs mass, because the Standard Model must stay a consistent theory up to the energy of inflation If the Higgs mass sits within a few hundred MeV of that bound, n_s and r depend on the top-quark and Higgs masses, and r can be well above 0.003 A higher reheating temperature than in Starobinsky R-squared inflation, which gives slightly different n_s and r and a different allowed range for the Higgs mass	Nearly scale-invariant spectrum of primordial density perturbations with scalar spectral index slightly less than 1 Approximately Gaussian, adiabatic primordial fluctuations Small but nonzero gravitational wave background depending on the potential shape
Where it breaks	Barbon and Espinosa argued in 2009 that the effective theory stops being valid at the Planck mass divided by the coupling, far below the field values inflation uses Burgess, Lee and Trott found in 2009 that the Hubble rate during inflation sits close to the scale where the semiclassical treatment breaks down Linking the inflationary parameters to collider measurements needs extra assumptions about the unknown high-energy completion, as Bezrukov and collaborators acknowledge The predictions nearly coincide with Starobinsky R-squared inflation and with a class of supergravity attractor models, so CMB data alone struggle to single out the Higgs ACT data combined with Planck, lensing and DESI give n_s = 0.974 ± 0.003. Some 2025 analyses read this as slightly above the simplest Higgs-inflation value, a tension that depends on the data combination and the model's high-energy details	Requires the inflaton to start very near the top of a flat potential, which is a finely tuned initial state. Realizing sufficiently flat small-field potentials compatible with particle physics is difficult; quantum corrections tend to spoil the required flatness. Specific potentials of this class are now disfavored or ruled out by Planck data, even though the slow-roll mechanism itself remains the working framework.
Key unresolved problem	The cutoff problem: the strong coupling to gravity lowers the energy at which the theory stops being reliable, so the flat plateau inflation needs depends on physics no one knows yet.	The flatness fine-tuning problem: the model needs an exceptionally flat potential for the field to roll down, but quantum corrections from particle physics tend to wrinkle that potential and ruin the flatness it depends on.
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Higgs Inflation

2008 · Strongly supported

New Inflation

1982 · Historical

Proposed

2008

1982

Key figures

Fedor Bezrukov, Mikhail Shaposhnikov

Andrei Linde, Andreas Albrecht, Paul Steinhardt

In one sentence

Bezrukov and Shaposhnikov proposed in 2008 that the Standard Model Higgs field drove inflation, provided it couples strongly to the curvature of spacetime, using only the particles of the Standard Model.

Linde and independently Albrecht and Steinhardt replaced Old Inflation's bubble nucleation with a scalar field slowly rolling down a flat potential, producing a coherent end to inflation across whole Hubble regions and the first viable predictions for cosmological perturbations.

Predictions

In the [[cosmic microwave background]], a spectral index n_s near 0.97 and a tensor-to-scalar ratio r near 0.003, almost independent of Standard Model parameters when the Higgs mass sits well above its critical value
A lower bound on the Higgs mass, because the Standard Model must stay a consistent theory up to the energy of inflation
If the Higgs mass sits within a few hundred MeV of that bound, n_s and r depend on the top-quark and Higgs masses, and r can be well above 0.003
A higher reheating temperature than in Starobinsky R-squared inflation, which gives slightly different n_s and r and a different allowed range for the Higgs mass

Nearly scale-invariant spectrum of primordial density perturbations with scalar spectral index slightly less than 1
Approximately Gaussian, adiabatic primordial fluctuations
Small but nonzero gravitational wave background depending on the potential shape

Where it breaks

Barbon and Espinosa argued in 2009 that the effective theory stops being valid at the Planck mass divided by the coupling, far below the field values inflation uses
Burgess, Lee and Trott found in 2009 that the Hubble rate during inflation sits close to the scale where the semiclassical treatment breaks down
Linking the inflationary parameters to collider measurements needs extra assumptions about the unknown high-energy completion, as Bezrukov and collaborators acknowledge
The predictions nearly coincide with Starobinsky R-squared inflation and with a class of supergravity attractor models, so CMB data alone struggle to single out the Higgs
ACT data combined with Planck, lensing and DESI give n_s = 0.974 ± 0.003. Some 2025 analyses read this as slightly above the simplest Higgs-inflation value, a tension that depends on the data combination and the model's high-energy details

Requires the inflaton to start very near the top of a flat potential, which is a finely tuned initial state.
Realizing sufficiently flat small-field potentials compatible with particle physics is difficult; quantum corrections tend to spoil the required flatness.
Specific potentials of this class are now disfavored or ruled out by Planck data, even though the slow-roll mechanism itself remains the working framework.

Key unresolved problem

The cutoff problem: the strong coupling to gravity lowers the energy at which the theory stops being reliable, so the flat plateau inflation needs depends on physics no one knows yet.

The flatness fine-tuning problem: the model needs an exceptionally flat potential for the field to roll down, but quantum corrections from particle physics tend to wrinkle that potential and ruin the flatness it depends on.

Reader vote

No votes yet