Abstract. We present an overview of scenarios where the observed Dark Matter (DM) abundance consists of Feebly Interacting Massive Particles (FIMPs), produced non-thermally by the so-called freeze-in mechanism. In contrast to the usual freeze-out scenario, frozen-in FIMP DM interacts very weakly with the particles in the visible sector and never attained thermal equilibrium with the baryon-photon fluid in the early Universe. Instead of being determined by its annihilation strength, the DM abundance depends on the decay and annihilation strengths of particles in equilibrium with the baryon-photon fluid, as well as couplings in the DM sector. This makes frozen-in DM very difficult but not impossible to test. In this review, we present the freeze-in mechanism and its variations considered in the literature (dark freeze-out and reannihilation), compare them to the standard DM freeze-out scenario, discuss several aspects of model building, and pay particular attention to observational properties and general testability of such feebly interacting DM.

We study the standard model (SM) in its full perturbative validity range between ΛQCD and the U (1)Y Landau pole, assuming that a yet unknown gravitational theory in the UV does not introduce additional particle thresholds, as suggested by the tiny cosmological constant and the absence of new stabilising physics at the EW scale. We find that, due to dimensional transmutation, the SM Higgs potential has a global minimum at 10 26 GeV, invalidating the SM as a phenomenologically acceptable model in this energy range. We show that extending the classically scale invariant SM with one complex singlet scalar S allows us to: (i) stabilise the SM Higgs potential; (ii) induce a scale in the singlet sector via dimensional transmutation that generates the negative SM Higgs mass term via the Higgs portal; (iii) provide a stable CP-odd singlet as the thermal relic dark matter due to CP-conservation of the scalar potential; (iv) provide a degree of freedom that can act as an inflaton in the form of the CP-even singlet. The logarithmic behaviour of dimensional transmutation allows one to accommodate the large hierarchy between the electroweak scale and the Landau pole, while understanding the latter requires a new non-perturbative view on the SM.

We propose a model of a confining dark sector, dark technicolor, that communicates with the Standard Model through the Higgs portal. In this model electroweak symmetry breaking and dark matter share a common origin, and the electroweak scale is generated dynamically. Our motivation to suggest this model is the absense of evidence for new physics from recent LHC data. Although the conclusion is far from certain at this point, this lack of evidence may suggest that no mechanism exists at the electroweak scale to stabilise the Higgs mass against radiative corrections from UV physics. The usual reaction to this puzzling situation is to conclude that the stabilising new physics is either hidden from us by accident, or that it appears at energies that are currently inaccessible, such that nature is indeed fine-tuned. In order to re-examine the arguments that have lead to this dichotomy, we review the concept of naturalness in effective field theories, discussing in particular the role of quadratic divergences in relation to different energy scales. This leads us to suggest classical scale invariance as a guidline for model building, implying that explicit mass scales are absent in the underlying theory. arXiv:1304.7006v2 [hep-ph]

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We consider an extension of the Standard Model with a singlet sector consisting of a real (pseudo)scalar and a Dirac fermion coupled with the Standard Model only via the scalar portal. We assume that the portal coupling is weak enough for the singlet sector not to thermalize with the Standard Model allowing the production of singlet particles via the freeze-in mechanism. If the singlet sector interacts with itself sufficiently strongly, it may thermalize within itself, resulting in dark matter abundance determined by the freeze-out mechanism operating within the singlet sector. We investigate this scenario in detail. In particular, we show that requiring the absence of inflationary isocurvature fluctuations provides lower bounds on the magnitude of the dark sector self-interactions and in parts of the parameter space favors sufficiently large self-couplings, supported also by the features observed in the small-scale structure formation.

Motivated by dark-photonγ scenarios extensively considered in the literature, we explore experimentally allowed models where the Higgs boson coupling to photon and dark photon Hγγ can be enhanced. Correspondingly, large rates for the H → γγ decay become plausible, giving rise to one monochromatic photon with E γ mH /2 (i.e., more than twice the photon energy in the rare standard-model decay H → γZ → γνν), and a similar amount of missing energy. We perform a model-independent study of this exotic resonant monophoton signature at the LHC, featuring a distinctive E γ T peak around 60 GeV, and γ + / E T transverse invariant mass ruled by mH . At parton level, we find a 5 σ sensitivity of the present LHC data set for a H → γγ branching fraction of 0.5%. Such large branching fractions can be naturally obtained in dark U (1)F models explaining the origin and hierarchy of the standard model Yukawa couplings. We urge the LHC experiments to search for this new exotic resonance in the present data set, and in future LHC runs.Introduction. Although dark matter (DM) is five times more abundant in the Universe than ordinary baryonic matter [1], its properties are yet unknown. It is plausible that the dark sector, which is weakly coupled to the standard model (SM), possesses rich internal structure and interactions. Among the most popular scenarios is the idea that the dark sector contains light or massless gauge bosons [2] that mediate long-range forces between dark particles. In cosmology the dark photons may solve the small-scale structure formation problems [3,4] and, for massless dark photons [5], predict dark discs of galaxies [6]. In astroparticle physics dark photons may induce Sommerfeld enhancement of DM annihilation cross section needed to explain the PAMELA-Fermi-AMS2 positron anomaly [7], may assist light DM annihilations to reach the phenomenologically required magnitude, and make asymmetric DM scenarios phenomenologically viable [8]. Dark/hidden photon scenarios have also been extensively considered in beyond-the-SM frameworks in particle physics [9][10][11][12][13][14][15].Recently, a new paradigm has been proposed for generating exponentially spread SM Yukawa couplings from unbroken U (1) F quantum numbers in the dark sector [16]. In this approach, nonperturbative flavor-and chiral-symmetry breaking is transferred from the dark to visible sector via heavy scalar messenger fields [16,17] In this work we show that, in the unbroken dark U (1) scenarios, the Higgs-boson two-body decay H → γγ to one photon γ and one dark photonγ can be enhanced despite existing constraints, providing a very distinctive NP signature of a single photon plus missing energy at the Higgs resonance. If this signature will be discovered at the LHC, CP invariance will imply the spin-1 nature of the missing energy, excluding axions or other ultralight scalar particles.Monophoton plus / E T signatures have been used by the LHC experiments to search for NP scenarios such as extra dimensions, supersymmetry, DM pair production [19], and SM con...

The CMS Collaboration has published two different searches for new physics that contain possible hints for excesses in eej j and eν j j final states. Interpreting those hints as a possible signal of a right-handed gauge boson W R with mass 2-2.5 TeV may have profound implications for our understanding of the gauge structure of nature and Grand Unification, the scalar sector accessible at the LHC, neutrino physics, and the baryon asymmetry of the Universe. We show that this interpretation is, indeed, consistent with all existing constraints. However, before making premature claims we propose a number of cross-checks at the LHC14 that could confirm or falsify this scenario. Those include searches for a Z R resonance and the related new scalar sector around 6-7 TeV. Additionally, large effects in top-quark spin-asymmetries in single top production are possible.

Supersymmetry in the gauge sector could be realized as N=1 or N=2 Supersymmetry, but the current LHC searches assume an N=1 realization. In this paper we show that squarks could be as light as few hundreds of GeV for N=2. We also describe an experimental procedure to count the number of supersymmetries, i.e. to distinguish between N=1 and N=2 supersymmetry, based on counting bins with different jet multiplicities and number of leptons.