| 1. |
- Abercrombie, Daniel, et al.
(författare)
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Dark Matter benchmark models for early LHC Run-2 Searches : Report of the ATLAS/CMS Dark Matter Forum
- 2020
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Ingår i: Physics of the Dark Universe. - : Elsevier BV. - 2212-6864. ; 27
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Tidskriftsartikel (refereegranskat)abstract
- This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.
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| 2. |
- Addazi, Andrea, et al.
(författare)
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QCD surprises : Strong CP problem, neutrino mass, Dark Matter and Dark Energy
- 2022
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Ingår i: Physics of the Dark Universe. - : Elsevier BV. - 2212-6864. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- An unexpected explanation for neutrino mass, Dark Matter (DM) and Dark Energy (DE) from genuine Quantum Chromodynamics (QCD) of the Standard Model (SM) is proposed here, while the strong CP problem is resolved without any need to account for fundamental axions. We suggest that the neutrino sector can be in a double phase in the Universe: i) relativistic neutrinos, belonging to the SM; ii) non-relativistic condensate of Majorana neutrinos. The condensate of neutrinos can provide an attractive alternative candidate for the DM, being in a cold coherent state. We will explain how neutrinos, combining into Cooper pairs, can form collective low-energy degrees of freedom, hence providing a strongly motivated candidate for the QCD (composite) axion.
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| 3. |
- Akrami, Yashar, et al.
(författare)
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Uncertainties in primordial black-hole constraints on the primordial power spectrum
- 2018
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Ingår i: Physics of the Dark Universe. - : ELSEVIER SCIENCE BV. - 2212-6864. ; 19, s. 124-128
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Tidskriftsartikel (refereegranskat)abstract
- The existence (and abundance) of primordial black holes (PBHs) is governed by the power spectrum of primordial perturbations generated during inflation. So far no PBHs have been observed, and instead, increasingly stringent bounds on their existence at different scales have been obtained. Up until recently, this has been exploited in attempts to constrain parts of the inflationary power spectrum that are unconstrained by cosmological observations. We first point out that the simple translation of the PBH non-observation bounds into constraints on the primordial power spectrum is inaccurate as it fails to include realistic aspects of PBH formation and evolution. We then demonstrate, by studying two examples of uncertainties from the effects of critical and non-spherical collapse, that even though they may seem small, they have important implications for the usefulness of the constraints. In particular, we point out that the uncertainty induced by non-spherical collapse may be much larger than the difference between particular bounds from PBH non-observations and the general maximum cap stemming from the condition Omega <= 1 on the dark-matter density in the form of PBHs. We therefore make the cautious suggestion of applying only the overall maximum dark-matter constraint to models of early Universe, as this requirement seems to currently provide a more reliable constraint, which better reflects our current lack of detailed knowledge of PBH formation. These, and other effects, such as merging, clustering and accretion, may also loosen constraints from non-observations of other primordial compact objects such as ultra-compact minihalos of dark matter.
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| 4. |
- Albert, Andreas, et al.
(författare)
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Recommendations of the LHC Dark Matter Working Group : Comparing LHC searches for dark matter mediators in visible and invisible decay channels and calculations of the thermal relic density
- 2019
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Ingår i: Physics of the Dark Universe. - : Elsevier BV. - 2212-6864. ; 26
-
Tidskriftsartikel (refereegranskat)abstract
- Weakly-coupled TeV-scale particles may mediate the interactions between normal matter and dark matter. If so, the LHC would produce dark matter through these mediators, leading to the familiar “mono-X” search signatures, but the mediators would also produce signals without missing momentum via the same vertices involved in their production. This document from the LHC Dark Matter Working Group suggests how to compare searches for these two types of signals in case of vector and axial-vector mediators, based on a workshop that took place on September 19/20, 2016 and subsequent discussions. These suggestions include how to extend the spin-1 mediated simplified models already in widespread use to include lepton couplings. This document also provides analytic calculations of the relic density in the simplified models and reports an issue that arose when ATLAS and CMS first began to use preliminary numerical calculations of the dark matter relic density in these models.
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| 5. |
- Alho, Artur, et al.
(författare)
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Quintessence from a state space perspective
- 2023
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Ingår i: Physics of the Dark Universe. - : Elsevier. - 2212-6864. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- We use dynamical systems methods to study quintessence models in a spatially flat and isotropic spacetime with matter and a scalar field with potentials for which lambda(v) = -V,v/V is bounded, thereby going beyond the exponential potential for which lambda(v) is constant. The scalar field equation of state parameter wv plays a central role when comparing quintessence models with observations, but with the dynamical systems used to date wv is an indeterminate, discontinuous, function on the state space in the asymptotically matter dominated regime. Our first main result is the introduction of new variables that lead to a regular dynamical system on a bounded three-dimensional state space on which wv is a regular function. The solution trajectories in the state space then provide a visualization of different types of quintessence evolution, and how initial conditions affect the transition between the matter and scalar field dominated epochs; this is complemented by graphs wv(N), where N is the e-fold time, which enables characterizing different types of quintessence evolution.
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| 6. |
- Alho, Artur, et al.
(författare)
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Tracking Quintessence
- 2024
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Ingår i: Physics of the Dark Universe. - : Elsevier. - 2212-6864. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- Tracking quintessence, in a spatially flat and isotropic space–time with a minimally coupled canonical scalar field and an asymptotically inverse power-law potential V(φ)∝φ−p, p>0, as φ→0, is investigated. This is done by introducing a new three-dimensional regular dynamical system, which enables a rigorous explanation of the tracking feature: (1) The dynamical system has a tracker fixed point T with a two-dimensional stable manifold that pushes an open set of nearby solutions toward a single tracker solution originating from T. (2) All solutions, including the tracker solution and the solutions that track/shadow it, end at a common future attractor fixed point that depends on the potential. Thus, the open set of solutions that shadow the tracker solution share its properties during the tracking quintessence epoch. We also discuss similarities and differences of underlying mechanisms for tracking, thawing and scaling freezing quintessence, and, moreover, we illustrate with state space pictures that all of these types of quintessence exist simultaneously for certain potentials.
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| 7. |
- Arguedas Cuendis, S., et al.
(författare)
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First results on the search for chameleons with the KWISP detector at CAST
- 2019
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Ingår i: Physics of the Dark Universe. - : Elsevier. - 2212-6864. ; 26
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Tidskriftsartikel (refereegranskat)abstract
- We report on a first measurement with a sensitive opto-mechanical force sensor designed for the direct detection of coupling of real chameleons to matter. These dark energy candidates could be produced in the Sun and stream unimpeded to Earth. The KWISP detector installed on the CAST axion search experiment at CERN looks for tiny displacements of a thin membrane caused by the mechanical effect of solar chameleons. The displacements are detected by a Michelson interferometer with a homodyne readout scheme. The sensor benefits from the focusing action of the ABRIXAS X-ray telescope installed at CAST, which increases the chameleon flux on the membrane. A mechanical chopper placed between the telescope output and the detector modulates the incoming chameleon stream. We present the results of the solar chameleon measurements taken at CAST in July 2017, setting an upper bound on the force acting on the membrane of 80pN at 95% confidence level. The detector is sensitive for direct coupling to matter 104≤βm≤108, where the coupling to photons is locally bound to βγ≤1011.
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| 8. |
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| 9. |
- Bull, Philip, et al.
(författare)
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Beyond ΛCDM : Problems, solutions, and the road ahead
- 2016
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Ingår i: Physics of the Dark Universe. - : Elsevier BV. - 2212-6864. ; 12, s. 56-99
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Tidskriftsartikel (refereegranskat)abstract
- Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, Lambda CDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of Lambda CDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.
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| 10. |
- Casalino, Alessandro, et al.
(författare)
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Mimicking dark matter and dark energy in a mimetic model compatible with GW170817
- 2018
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Ingår i: Physics of the Dark Universe. - : Elsevier BV. - 2212-6864. ; 22, s. 108-115
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Tidskriftsartikel (refereegranskat)abstract
- The recent observation of the gravitational wave event GW170817 and of its electromagnetic counterpart GRB170817A, from a binary neutron star merger, has established that the speed of gravitational waves deviates from the speed of light by less than one part in 10(15). As a consequence, many extensions of General Relativity are inevitably ruled out. Among these we find the most relevant sectors of Horndeski gravity. In its original formulation, mimetic gravity is able to mimic cosmological dark matter, has tensorial perturbations that travel exactly at the speed of light but has vanishing scalar perturbations and this fact persists if we combine mimetic with Horndeski gravity. In this work, we show that implementing the mimetic gravity action with higher-order terms that break the Horndeski structure yields a cosmological model that satisfies the constraint on the speed of gravitational waves and mimics both dark energy and dark matter with a non-vanishing speed of sound. In this way, we are able to reproduce the Lambda CDM cosmological model without introducing particle cold dark matter.
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