| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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