Browsing by Subject "particle physics - cosmology connection"

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  • Enqvist, Kari; Hardwick, Robert J.; Tenkanen, Tommi; Vennin, Vincent; Wands, David (2018)
    We show that in the Feebly Interacting Massive Particle (FIMP) model of Dark Matter (DM), one may express the inflationary energy scale H-* as a function of three otherwise unrelated quantities, the DM isocurvature perturbation amplitude, its mass and its self-coupling constant, independently of the tensor-to-scalar ratio. The FIMP model assumes that there exists a real scalar particle that alone constitutes the DM content of the Universe and couples to the Standard Model via a Higgs portal. We consider carefully the various astrophysical, cosmological and model constraints, accounting also for variations in inflationary dynamics and the reheating history, to derive a robust estimate for H-* that is con fined to a relatively narrow range. We point out that, within the context of the FIMP DM model, one may thus determine H-* reliably even in the absence of observable tensor perturbations.
  • Beltran Almeida, Juan P.; Bernal, Nicolas; Rubio, Javier; Tenkanen, Tommi (2019)
    If cosmic inflation was driven by an electrically neutral scalar field stable on cosmological time scales, the field necessarily constitutes all or part of dark matter (DM). We study this possibility in a scenario where the inflaton field s resides in a hidden sector, which is coupled to the Standard Model sector through the Higgs portal lambda(hs)s(2) (HH)-H-dagger and non-minimally to gravity via xi(s)s(2)R. We study scenarios where the field s first drives inflation, then reheats the Universe, and later constitutes all DM. We consider two benchmark scenarios where the DM abundance is generated either by production during reheating or via non-thermal freeze-in. In both cases, we take into account all production channels relevant for DM in the mass range from keV to PeV scale. On the inflationary side, we compare the dynamics and the relevant observables in two different but well-motivated theories of gravity (metric and Palatini), discuss multi field effects in case both fields (s and h) were dynamical during inflation, and take into account the non-perturbative nature of particle production during reheating. We find that, depending on the initial conditions for inflation, couplings and the DM mass, the scenario works well especially for large DM masses, 10(2) GeV less than or similar to m(s) less than or similar to 10(6) GeV, although there are also small observationally allowed windows at the keV and MeV scales. We discuss how the model can be tested through astrophysical observations.
  • Enckell, Vera-Maria; Enqvist, Kari; Räsänen, Syksy; Tomberg, Eemeli (2018)
    We study inflation with the non-minimally coupled Standard Model Higgs in the case when quantum corrections generate a hilltop in the potential. We consider both the metric and the Palatini formulation of general relativity. We investigate hilltop inflation in different parts of the Higgs potential and calculate predictions for CMB observables. We run the renormalization group equations up from the electroweak scale and down from the hilltop, adding a jump in-between to account for unknown corrections in the intermediate regime. Within our approximation, no viable hilltop inflation is possible for small field values, where the non-minimal coupling has no role, nor for intermediate field values. For large field values, hilltop inflation works. We find the spectral index to be n(s)
  • Räsänen, Syksy; Wahlman, Pyry (2017)
    We compare Higgs inflation in the metric and Palatini formulations of general relativity, with loop corrections treated in a simple approximation. We consider Higgs inflation on the plateau, at a critical point, at a hilltop and in a false vacuum. In the last case there are only minor differences. Otherwise we find that in the Palatini formulation the tensor-to-scalar ratio is consistently suppressed, spanning the range 1 x 10-(13) <r <7 x 10(-5), compared to the metric case result 2 x 10(-5) <r <0.2. Even when the values of n(s) and r overlap, the running and running of the running are different in the two formulations. Therefore, if Higgs is the inflaton, inflationary observables can be used to distinguish between different gravitational degrees of freedom, in this case to determine whether the connection is an independent variable. Non-detection of r in foreseeable future observations would not rule out Higgs inflation, only its metric variant. We conclude that in order to fix the theory of Higgs inflation, not only the particle physics UV completion but also the gravitational degrees of freedom have to be explicated.
  • Decant, Quentin; Heisig, Jan; Hooper, Deanna C.; Lopez-Honorez, Laura (2022)
    Dark matter (DM) from freeze-in or superWIMP production is well known to imprint non-cold DM signatures on cosmological observables. We derive constraints from Lyman-a forest observations for both cases, basing ourselves on a reinterpretation of the existing Lyman-a limits on thermal warm DM. We exclude DM masses below 15 keV for freeze-in, in good agreement with previous literature, and provide a generic lower mass bound for superWIMPs that depends on the mother particle decay width. Special emphasis is placed on the mixed scenario, where contributions from both freeze-in and superWIMP are similarly important. In this case, the imprint on cosmological observables can deviate significantly from thermal warm DM. Furthermore, we provide a modified version of the Boltzmann code CLASS, analytic expressions for the DM distributions, and fits to the DM transfer functions that account for both mechanisms of production. Moreover, we also derive generic constraints from ANeff measurements and show that they cannot compete with those arising from Lyman-alpha observations. For illustration, we apply the above generic limits to a coloured t-channel mediator DM model, in which case contributions from both freeze-in through scatterings and decays, as well as superWIMP production can be important. We map out the entire cosmologically viable parameter space, cornered by bounds from Lyman-alpha observations, the LHC, and Big Bang Nucleosynthesis.
  • Enckell, Vera-Maria; Enqvist, Kari; Nurmi, Sami (2016)
    We investigate the dependency of Higgs inflation on the non-renormalisable matching between the low energy Standard Model limit and the inflationary regime at high energies. We show that for the top mass range m(t) greater than or similar to 171.8 GeV the scenario robustly predicts the spectral index n(s) similar or equal to 0.97 and the tensor-to-scalar ratio r similar or equal to 0.003. The matching is however non-trivial, even the best-fit values m(h) = 125.09 GeV and m(t) = 173.21 GeV require a jump delta lambda similar to 0.01 in the Higgs coupling below the inflationary scale. For m(t) less than or similar to 171.8 GeV, the matching may generate a feature in the inflationary potential. In this case the predicted values of n(s) and r vary but the model is still falsifiable. For example, a detection of negative running of spectral index at level alpha(s) less than or similar to -0.01 would rule out Higgs inflation.
  • Bernal, Nicolas; Rubio, Javier; Veermäe, Hardi (2020)
    In the Starobinsky model of inflation, the observed dark matter abundance can be produced from the direct decay of the inflaton field only in a very narrow spectrum of closeto-conformal scalar fields and spinors of mass similar to 10(7) GeV. This spectrum can be, however, significantly broadened in the presence of effective non-renormalizable interactions between the dark and the visible sectors. In particular, we show that UV freeze-in can efficiently generate the right dark matter abundance for a large range of masses spanning from the keV to the PeV scale and arbitrary spin, without significantly altering the heating dynamics. We also consider the contribution of effective interactions to the inflaton decay into dark matter.