| 1. |
- Abdalla, E., et al.
(författare)
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Cosmology intertwined : A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies
- 2022
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Ingår i: Journal of High Energy Astrophysics. - : Elsevier BV. - 2214-4048 .- 2214-4056. ; 34, s. 49-211
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Tidskriftsartikel (refereegranskat)abstract
- The standard Λ Cold Dark Matter (ΛCDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant H0, the σ8–S8 tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the 5.0σ tension between the Planck CMB estimate of the Hubble constant H0 and the SH0ES collaboration measurements. After showing the H0 evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density Ωm, and the amplitude or rate of the growth of structure (σ8,fσ8). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the H0–S8 tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questions.
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| 2. |
- Avgoustidis, Anastasios, et al.
(författare)
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Deconstructing higher order clockwork gravity
- 2021
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Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 103:12
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Tidskriftsartikel (refereegranskat)abstract
- We consider the higher order clockwork theory of gravitational interactions, whereby a number of gravitons are coupled together with TeV strength, but nevertheless generate a Planck scale coupling to matter without the need for a dilaton. It is shown that the framework naturally lends itself to a five-dimensional geometry, and we find the 5D continuum version of such deconstructed 4D gravitational clockwork models. Moreover, the clockwork picture has matter coupled to particular gravitons, which in the 5D framework looks like a braneworld model, with the Randall-Sundrum model being a special case. More generally, the gravitational clockwork leads to a family of scalar-tensor braneworld models, where the scalar is not a dilaton.
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| 3. |
- Bernardo, Heliudson, et al.
(författare)
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Modified Gravity Approaches to the Cosmological Constant Problem
- 2023
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Ingår i: Universe. - : MDPI. - 2218-1997. ; 9:2
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Forskningsöversikt (refereegranskat)abstract
- The cosmological constant and its phenomenology remain among the greatest puzzles in theoretical physics. We review how modifications of Einstein's general relativity could alleviate the different problems associated with it that result from the interplay of classical gravity and quantum field theory. We introduce a modern and concise language to describe the problems associated with its phenomenology, and inspect no-go theorems and their loopholes to motivate the approaches discussed here. Constrained gravity approaches exploit minimal departures from general relativity; massive gravity introduces mass to the graviton; Horndeski theories lead to the breaking of translational invariance of the vacuum; and models with extra dimensions change the symmetries of the vacuum. We also review screening mechanisms that have to be present in some of these theories if they aim to recover the success of general relativity on small scales as well. Finally, we summarize the statuses of these models in their attempts to solve the different cosmological constant problems while being able to account for current astrophysical and cosmological observations.
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| 4. |
- Copeland, Edmund J., et al.
(författare)
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Generalised scalar-tensor theories and self-tuning
- 2022
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- We explore a family of generalised scalar-tensor theories that exhibit self-tuning to low scale anti de Sitter vacua, even in the presence of a large cosmological constant. We are able to examine the linearised fluctuations about these vacua and compute the corresponding amplitude. Thanks to a subtle interplay between a weak scalar coupling and a low scalar mass, it is possible to exhibit self-tuning and compatibility with solar system tests of gravity without resorting to non-linearities and unreliable screening mechanisms. The weakness of the scalar coupling and the correspondingly slow response to vacuum energy phase transitions may present some interesting possibilities for connecting early universe inflation to the cancellation of vacuum energy.
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| 5. |
- Cruz, Juan S., et al.
(författare)
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A grounded perspective on new early dark energy using ACT, SPT, and BICEP/Keck
- 2023
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :2
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Tidskriftsartikel (refereegranskat)abstract
- We examine further the ability of the New Early Dark Energy model (NEDE) to resolve the current tension between the Cosmic Microwave Background (CMB) and local measurements of H0 and the consequences for inflation. We perform new Bayesian analyses, including the current datasets from the ground-based CMB telescopes Atacama Cosmology Telescope (ACT), the South Pole Telescope (SPT), and the BICEP/Keck telescopes, employ-ing an updated likelihood for the local measurements coming from the SH0ES collaboration. Using the SH0ES prior on H0, the combined analysis with Baryonic Acoustic Oscillations (BAO), Pantheon, Planck and ACT improves the best-fit by Delta chi 2 = -15.9 with respect to ACDM, favors a non-zero fractional contribution of NEDE, fNEDE > 0, by 4.8a, and gives a best-fit value for the Hubble constant of H0 = 72.09 km/s/Mpc (mean 71.49 +/- 0.82 with 68% C.L.). A similar analysis using SPT instead of ACT yields consistent results with a Delta chi 2 = -23.1 over ACDM, a preference for non-zero fNEDE of 4.7a and a best-fit value of H0 = 71.77 km/s/Mpc (mean 71.43 +/- 0.85 with 68% C.L.). We also provide the constraints on the inflation parameters r and ns coming from NEDE, including the BICEP/Keck 2018 data, and show that the allowed upper value on the tensor-scalar ratio is consistent with the ACDM bound, but, as also originally found, with a more blue scalar spectrum implying that the simplest curvaton model is now favored over the Starobinsky inflation model.
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| 6. |
- Cruz, Juan S., et al.
(författare)
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Cold New Early Dark Energy pulls the trigger on the H 0 and S 8 tensions: a simultaneous solution to both tensions without new ingredients
- 2023
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; 2023:11
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we show that the Cold New Early Dark Energy (Cold NEDE) model in its original form can solve both the Hubble tension and the S 8 tension without adding any new ingredients at the fundamental level. So far, it was assumed that the trigger field in the Cold NEDE model is completely subdominant. However, relaxing this assumption and letting the trigger field contribute a mere 0.5% of the total energy density leads to a resolution of the S 8 tension while simultaneously improving it as a solution to the H 0 tension. Fitting this model to baryonic acoustic oscillations, large-scale-structure, supernovae (including a SH0ES prior), and cosmic microwave background data, we report a preferred NEDE fraction of f NEDE = 0.134+0.032-0.025 (68% C.L.), lifting its Gaussian evidence for the first time above 5σ (up from 4σ when the trigger contribution to dark matter is negligible). At the same time, we find the new concordance values H 0 = 71.71 ± 0.88 km sec-1 Mpc-1 and S 8 = 0.793 ± 0.018. Excluding large-scale structure data and the SH0ES prior, both Gaussian tensions are reduced below the 2σ level.
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| 7. |
- Cruz, Juan S., et al.
(författare)
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NANOGrav meets Hot New Early Dark Energy and the origin of neutrino mass
- 2023
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 846
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been speculated that the NANOGrav observations point towards a first-order phase transition in the dark sector at the GeV scale [1]. Here, we show that such a phase transition might already have been predicted in the Hot New Early Dark Energy model (Hot NEDE) [2,3]. There, it was argued that two dark sector phase transitions are the signature of neutrino mass generation through the inverse seesaw mechanism. In particular, an IR phase transition serves a double purpose by resolving the Hubble tension through an energy injection and generating the Majorana mass entry in the inverse seesaw mixing matrix. This usual NEDE phase transition is then accompanied by a UV counterpart, which generates the heavy Dirac mass entry in the inverse seesaw mass matrix of a right-handed neutrino. Here, we investigate if the UV phase transition of the Hot NEDE model can occur at the GeV scale in view of the recent NANOGrav observations.
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| 8. |
- Cruz, Juan S., et al.
(författare)
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Profiling cold new early dark energy
- 2023
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Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 108:2
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Tidskriftsartikel (refereegranskat)abstract
- Recent interest in new early dark energy (NEDE), a cosmological model with a vacuum energy component decaying in a triggered phase transition around recombination, has been sparked by its impact on the Hubble tension. Previous constraints on the model parameters were derived in a Bayesian framework with Markov-chain Monte Carlo (MCMC) methods. In this work, we instead perform a frequentist analysis using the profile likelihood in order to assess the impact of prior volume effects on the constraints. We constrain the maximal fraction of NEDE fNEDE, finding fNEDE=0.076-0.035+0.040 at 68% CL with our baseline dataset and similar constraints using either data from SPT-3G, ACT or full-shape large-scale structure, showing a preference over ΛCDM even in the absence of a SH0ES prior on H0. While this is stronger evidence for NEDE than obtained with the corresponding Bayesian analysis, our constraints broadly match those obtained by fixing the NEDE trigger mass. Including the SH0ES prior on H0, we obtain fNEDE=0.136-0.026+0.024 at 68% CL. Furthermore, we compare NEDE with the early dark energy (EDE) model, finding similar constraints on the maximal energy density fractions and H0 in the two models. At 68% CL in the NEDE model, we find H0=69.56-1.29+1.16 km s-1 Mpc-1 with our baseline and H0=71.62-0.76+0.78 km s-1 Mpc-1 when including the SH0ES measurement of H0, thus corroborating previous conclusions that the NEDE model provides a considerable alleviation of the H0 tension.
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| 9. |
- Flinckman, Joakim, 1990-
(författare)
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Beyond Bimetric Theory: Consistent Theories of Multiple Spin-2 Fields
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The mathematical formulations of the fundamental interactions in nature are all expressed in terms of fields classified by their mass and spin. Two of the most successful theories in physics, general relativity and the standard model, can both, in principle, be derived uniquely from fields with fixed mass and spin, guided by theoretical considerations such as consistency. The standard model contains well-understood interactions of particles with spins less than two, while theories involving spins higher than two are generally problematic. Theories of spin-2 fields are much less explored, and specifically, any consistent multiplet structure, crucial for the standard model, is practically unknown. In pursuit of such structures, this thesis delves into theories of multiple spin-2 fields, examining interactions with a focus on couplings that extend beyond bimetric interactions and concentrating on their consistency, field content, and mass spectrum.
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| 10. |
- Hofmann, Stefan, et al.
(författare)
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Perturbative quantum consistency near black-hole horizon formation
- 2021
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Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 104:12
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Tidskriftsartikel (refereegranskat)abstract
- We study the prelude to black-hole formation using a suspended shell composed of physical matter that fulfills the dominant energy condition. Here, the collapse of the shell is brought to rest when the formation of the horizon is imminent but has not yet occurred. As the main achievement of this work, we obtain the Feynman propagator which connects the interior and the exterior of the shell within two local coordinate patches. It is derived by drawing an analogy to the propagation of light across interfaces that separate regions with different susceptibilities inside a medium. As a first application, we use this propagator to determine the vacuum persistence amplitude in the presence of external sources. On timescales much shorter than the Page time, we find that the amplitude builds up with time yet remains consistent with perturbative unitarity.
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