We show that quantum-induced marginal deformations of the Starobinsky gravitational action of the form R 2(1−α) , with R the Ricci scalar and α a positive parameter smaller than one half, can generate sizable primordial tensor modes. We also suggest natural microscopic sources of these corrections and demonstrate that they generally lead to a nonzero and positive α. Furthermore we argue, that within this framework, the scalar spectral index and tensor modes probe theories of grand unification including theories not testable at the electroweak scale.
We consider three classes of dark matter (DM) models to account for the recently observed 3.5 keV line: metastable excited state DM, annihilating DM, and decaying DM. We study two examples of metastable excited state DM. The first, millicharged composite DM, has both inelasticity and photon emission built in, but with a very constrained parameter space. In the second example, up-scattering and decay come from separate sectors and is thus less constrained. The decay of the excited state can potentially be detectable at direct detection experiments. However we find that CMB constraints are at the border of excluding this as an interpretation of the DAMA signal. The annihilating DM interpretation of the X-ray line is found to be in mild tension with CMB constraints. Lastly, a generalized version of decaying DM can account for the data with a lifetime exceeding the age of the Universe for masses 10 6 GeV.
We analyze quantum corrections on the naive φ 4 -Inflation. These typically lead to an inflaton potential which carries a non-integer power of the field. We consider both minimal and non-minimal couplings to gravity. For the latter case we also study unitarity of inflaton-inflaton scattering. Finally we confront these theories with the Planck and BICEP2 data. We demonstrate that the presence of nonvanishing primordial tensor modes requires sizable quantum departures from the φ 4 -Inflaton model for the non-minimally coupled scenario which we parametrize and quantify. We compare the results with the minimally coupled case and elucidate the main distinctive features. I. NON-MINIMALLY COUPLED THEORIES WITH QUANTUM POTENTIALSThe underlying origin of the inflationary paradigm constitutes a prominent problem in cosmology [1][2][3][4][5][6]. Inflation is traditionally modelled via the introduction of new scalar fields. Many models have been put forward to describe the dynamics of these scalar fields and their interactions with other fields, as it has been recently reviewed in [7].On general grounds any renormalizable field theory will recieve quantum corrections to the potential. One can think of the E. Weinberg and Coleman perturbative quantum corrections to the classical scalar potential of any field theory as a simple example of these type of corrections [8,9]. We phenomenologically characterize these corrections to the φ 4 theory by introducing a real parameter γ as follows:with Λ a given energy scale. Of course, model by model, one can compute the specific potential as in [10]. Nevertheless we will show that it is possible to provide useful information on a large class of models corresponding to different values of γ using this simple approach. For completeness we analyze the cases in which φ couples both minimally and non-minimally to gravity. We find that for the non-minimally coupled case, the recent results by BICEP2 indicating the presence of primordial tensor modes [11] constrains γ to lie in the region 0.08 − 0.12, at the two-sigma confidence level. However, independently on the validity of the BICEP2 results [12,13], it is fundamental to know whether quantum corrected potentials can account for nonzero tensor modes.Interestingly, we also discover that for large primordial tensor modes the results are largely independent on the number of e-foldings. Relevant examples of nonminimally coupled models are the Higgs-Inflation model [14] and the ones in which the inflaton is a composite state [15][16][17][18]. II. COUPLING TO GRAVITY AND SLOW-ROLL INFLATIONWe consider the action of a scalar field non-minimally coupled to gravity:The subscript J refers to the Jordan frame, and indicates that the gravity sector is not of the Einstein Hilbert form. Generally in the Jordan frame, the scalar background contributes to the effective Planck mass: M 2 P = M 2 +ξ φ 2 . However, φ 2 = 0 in the present case and we can safely identify M with M P .
We investigate models in which inflation is driven by an ultraviolet safe and interacting scalar sector stemming from a new class of nonsupersymmetric gauge field theories. These new theories, differently from generic scalar models, are well defined to arbitrary short distances because of the existence of a controllable ultraviolet interacting fixed point. The scalar couplings at the ultraviolet fixed point and their overall running are predicted by the geometric structure of the underlying theory. We analyse the minimal and non-minimal coupling to gravity of these theories and the consequences for inflation. In the minimal coupling case the theory requires large non-perturbative quantum corrections to the quantum potential for the theory to agree with data, while in the nonminimal coupling case the perturbative regime in the couplings of the theory is preferred. Requiring the theory to reproduce the observed amplitude of density perturbations constrain the geometric data of the theory such as the number of colors and flavors for generic values of the non-minimal coupling.Preprint: CP 3 -Origins-2015-008 DNRF90The inflationary paradigm plays a central role in modern cosmology [1,2]. Many realisations have appeared in the literature [3] with the vast majority using elementary scalar fields to drive inflation. Theories with fundamental scalars are, however, typically trivial. Meaning that for the theory to be well defined at arbitrary short scales the renormalized coupling must vanish, and consequently the resulting theory is non-interacting. It could happen that gravitational corrections can render field theories featuring scalars well defined at short distances, but so far no formal proof exists in four dimensions, and without requiring additional (space-time) symmetries. It is therefore interesting to explore models where the issue is resolved before the underlying fundamental particle theory of the inflaton is coupled to gravity. A possible solution is to assume the inflaton to be a composite state made by a more fundamental matter [4,5] governed by an asymptotically free theory [6,7]. The gravity dual dynamics of these models has been investigated in [8].Recently, however, a novel class of non-trivial fourdimensional theories featuring elementary scalars appeared [9]. The crucial ingredient is the presence of an exact interacting ultraviolet (UV) fixed point in all the couplings of the theory, i.e. the theories are complete asymptotically safe [9]. The asymptotic safety scenario refers to the existence of high-energy fixed points [10]. It plays a relevant role as a possible UV completion of quantum gravity [10][11][12][13][14] 1 . The resulting physics is quite distinct from the tra-1 In addition several UV conformal extensions of the standard ditional complete asymptotic freedom scenario where a non-interacting UV fixed point emerges in all the couplings [44,45]; see also [46,47] for recent studies.The template that we shall consider here consists of an SU (N C ) gauge theory with N F Dirac fermions transfor...
We study phenomenological constraints in a simple SEχy extension of the Standard Model (SM) with a 125 GeV Higgs, a vectorlike heavy electron (E), a complex scalar electron (S) and a standard model singlet Dirac fermion (χ). The interactions among the dark matter candidate χ and the standard model particles occur via loop-induced processes involving the Yukawa interaction SEχy. The model is an explicit perturbative realization of so-called magnetic dark matter. The field content allows for a cancelation of quadratic divergences in the scalar masses at one-loop, a phenomenon which we refer to as perturbative naturality. The basic model is constrained dominantly by direct detection experiments and its parameter space can be nearly entirely covered by up-coming ton-scale direct detection experiments. We conclude this work by discussing different variations of the model.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.