We show that introducing R 2 -term makes the Higgs-inflation and Higgs-dilaton inflation consistent models: the strong coupling energy scales in scalar, gauge and gravity sectors all are lifted up to the Planck scale.

Exploring the WEP with a pulsed cold beam of antihydrogen View the table of contents for this issue, or go to the journal homepage for more 2012 Class. Quantum Grav. 29 184009

Strong coupling in Higgs inflation at high energies hinders a joint description of inflation, reheating and low-energy dynamics. The situation may be improved with a proper UV completion of the model. A well-defined self-consistent way is to introduce an R 2 -term into the action. In this modified model the strong coupling scale returns back to the Planck scale, which justifies the use of the perturbative methods in studies of the model dynamics after inflation. We investigate the reheating of the post-inflationary Universe, which involves two highly anharmonic oscillators strongly interacting with each other: homogeneous Higgs field and scalaron. We observe that in interesting regions of model parameter space these oscillations make longitudinal components of the weak gauge bosons tachyonic, triggering instant preheating at timescales much shorter than the Hubble time. The weak gauge bosons are heavy and decay promptly into light Standard Model particles, ensuring the onset of the radiation domination era right after inflation.Email addresses: Fedor.Bezrukov@manchester.ac.uk (Fedor Bezrukov), gorby@ms2.inr.ac.ru (Dmitry Gorbunov), christopher.shepherd-3@postgrad.manchester.ac.uk (Chris Shepherd), tokareva@ms2.inr.ac.ru (Anna Tokareva)

We introduce conformal coupling of the Standard Model Higgs field to gravity and discuss the subsequent modification of R 2 -inflation. The main observation is a lower temperature of reheating which happens mostly through scalaron decays into gluons due to the conformal (trace) anomaly. This modifies all predictions of the original R 2inflation. To the next-to-leading order in slow roll parameters we calculate amplitudes and indices of scalar and tensor perturbations produced at inflation. The results are compared to the next-to-leading order predictions of R 2 -inflation with minimally coupled Higgs field and of Higgs-inflation. We discuss additional features in gravity wave signal that may help to distinguish the proposed variant of R 2 -inflation. Remarkably, the features are expected in the region available for study at future experiments like BBO and DECIGO. Finally, we check that (meta)stability of electroweak vacuum in the cosmological model is consistent with recent results of searches for the Higgs boson at LHC. arXiv:1212.4466v2 [astro-ph.CO] 6 Dec 2013In this paper we consider the Starobinsky inflation with matter sector described by the Standard Model of particle physics (SM) which scalar sector is slightly modified. Namely, we add a conformal coupling of the SM Higgs field to gravity. This term leaves intact the low energy phenomenology of the SM, but impacts on the history of the early Universe. Indeed, we found that with the Higgs boson becoming conformal at high energies, reheating of the Universe takes place later and occurs via gluon production due to the conformal (trace) anomaly. The idea of conformal anomaly being responsible for reheating was discussed in literature, e.g., [3,4]. Here it is natural consequence of the conformal symmetry in our model.Lower reheating temperature implies longer matter dominated stage between inflation and reheating. This modifies all predictions for power spectra of scalar and tensor perturbations generated at inflation. Likewise, this modifies predictions for gravity wave signals expected from nonlinear structure dynamics at post-inflationary stage. These are special signals in gravity waves given the long-lasting post-inflationary matter dominated stage. Remarkably, the signals fall in the region expected to be reached by proposed future experiments like BBO [5] and DECIGO [6] on searches for gravity waves. These signals have been proposed [7] as signatures of R 2 -inflation. The same is true for our variant with conformal Higgs, where the features in gravity wave spectrum are expected at different frequencies, which allows to test the model. Finally, the non-minimal coupling provides with additional term in the Higgs effective potential, which becomes important at large scalar curvature. This can change the answer to the question: in which vacuum does the Higgs field fall in the expanding Universe, given the value of the Higgs self-coupling (or the Higgs boson mass)?We address all these issues below. The model is presented in Sec. 2, and reheating is studied...

Recent cosmological data favour R^2-inflation and some amount of non-standard dark radiation in the Universe. We show that a framework of high energy scale invariance can explain these data. The spontaneous breaking of this symmetry provides gravity with the Planck mass and particle physics with the electroweak scale. We found that the corresponding massless Nambu--Goldstone bosons -- dilatons -- are produced at reheating by the inflaton decay right at the amount needed to explain primordial abundances of light chemical elements and anisotropy of the cosmic microwave background. Then we extended the discussion on the interplay with Higgs-inflation and on general class of inflationary models where dilatons are allowed and may form the dark radiation. As a result we put a lower limit on the reheating temperature in a general scale invariant model of inflation.Comment: 15 pages, 4 figures; v2: replaced with revised version recently publishe