Cosmic inflation solves the horizon and flatness problems, but its main actor — the inflaton — is usually thought to be hidden behind the Planck curtain. The light inflaton scenario turns it into a bridge: the same inflaton, mixing with the Higgs boson, can show up in terrestrial detectors. Recent results on the cosmic microwave background from ACT added intrigue: a shift of the spectral index ns toward larger values forces us to re‑examine how sturdy this bridge's construction is.
The theoretical framework is general relativity with a non‑minimal coupling between the inflaton and gravity in the Jordan frame. After a conformal transformation one obtains the Einstein frame with a canonical field and a flat potential. Radiative corrections to the self‑coupling constant are described by the parameter ΔL. Slow‑roll yields predictions for the spectral index ns and the tensor-to-scalar ratio r, which are then confronted with Planck+ACT+DESI+BICEP/Keck data. On the laboratory shore of the bridge lies the phenomenology of mixing with the Higgs: decays K→π+invisible, B→K+μμ, searches for displaced vertices. Decay probabilities inside the detector are computed for three regimes: escaping, prompt, and displaced. The contribution of a virtual inflaton to B0‑meson oscillations, which is independent of its lifetime, is also taken into account. For primordial nucleosynthesis a lower limit of 4 MeV on the reheating temperature is imposed.
The bridge holds the load. For ns=0.965 the model with non‑minimal coupling ξφ and radiative correction ΔL falls within the 2σ region of ACT, and for ΔL≈0.03–0.05 it enters the 1σ region. Without corrections (ΔL=0) the prediction falls outside the 2σ range of ACT while remaining inside the 2σ range of Planck. The number of e‑folds Nk≈55 is almost insensitive to the reheating temperature Trh if the equation‑of‑state parameter wr=1/3. The laboratory beams of the bridge have already been tested: existing experiments (NA62, LHCb, BaBar) exclude sinθ≳$10^{-3}$ for mφ=0.1–1 GeV, and B0 oscillations give a linear limit sinθ < mφ/GeV. Future pillars — MATHUSLA, SHiP, FASER2 — will reach down to Trh<1 GeV. If the inflaton partially decays into dark matter with a branching ratio B∼$10^{-11}$–$10^{-7}$, then for mDM=mφ/3 the observed density is reproduced.
The built bridge means that inflation ceases to be a purely cosmological hypothesis. Direct detection of the inflaton would be an independent confirmation, on par with the detection of primordial gravitational waves. Laboratory limits already cut off large mixing angles, and the combined requirements of reheating and dark matter pin down the parameters of the bridge.
New data on the cosmic microwave background (Planck, ACT, future CMB‑S4) and surveys of large‑scale structure (Euclid, SPHEREx) will refine ns and r, shrinking the allowed region. Experiments such as DUNE, SHADOWS, and Codex‑b will add sensitivity on the laboratory shore.
The theory of inflation, physics of the Higgs sector, searches for dark matter.
Accounting for non‑perturbative effects during reheating, thermal corrections to the Higgs potential, and quantum fluctuations during inflation; calculation of the dark matter production cross section in specific models.
The nature of dark matter and the hierarchy problem find a natural arena in the light inflaton scenario. Choosing the potential from the multitude of inflationary models remains an open question.
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What the work does
This work builds a bridge between cosmic inflation and laboratory physics through a light inflaton scenario that mixes with the Higgs boson. The authors compute predictions for the spectral index and the tensor-to-scalar ratio, confronting them with data from Planck, ACT, DESI, and BICEP/Keck, and also analyze constraints from K and B meson decays and B0 oscillations. They show that the model with radiative corrections falls within the 1σ region of ACT for certain parameter values, and outline prospects for searches at future experiments like MATHUSLA.
Where its strength is
The strength of the work lies in uniting inflationary cosmology and collider phenomenology: the same set of parameters simultaneously satisfies cosmic microwave background data and laboratory constraints, and can also explain dark matter. This turns the inflaton into a testable particle rather than an abstract field behind the Planck curtain.
Where it could go next
Worth trying
Why this may matter
If a light inflaton is discovered in laboratory experiments, it would provide direct evidence for inflation, independent of gravitational waves, and connect physics at scales of 10⁻³⁵ m with accelerator scales. Simultaneously explaining dark matter with the same field could close several open problems of the Standard Model in a unified picture.
Nearby works in our archive
The closest work in the archive sits at 0.68 by meaning — the usual level for our corpus.
as written by the authors arXiv:2607.23200v1
We investigate the viability of the light inflaton scenario in light of the latest inflationary constraints from the Atacama Cosmology Telescope (ACT), together with bounds from collider and intensity-frontier experiments searching for a feebly coupled light scalar with a sub-GeV mass. Assuming a quartic inflaton potential, we identify the region of parameter space consistent with the ACT observations and derive constraints on the inflaton mass and inflaton-Higgs mixing using results from NA62, KOTO, BaBar, Belle, LHCb, MATHUSLA, FASER2, SHiP, and neutral meson oscillations. We also explore the prospects for dark matter production during reheating within this framework, while remaining consistent with the inflationary observables.
The predecessor article was called 'Light Inflaton Hunter's Guide' — an allusion to the famous guide 'The Hitchhiker's Guide to the Galaxy.' Inflaton hunters are armed not with a towel but with data from B‑factories and telescopes.