Ref HAL: hal-03184607_v1
DOI: 10.1103/PhysRevD.103.023526
WoS: WOS:000609014700004
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We consider the possibility that the dark sector of our Universe contains a negative cosmological constant dubbed λ. For such models to be viable, the dark sector should contain an additional component responsible for the late-time accelerated expansion rate (X). We explore the departure of the expansion history of these models from the concordanceΛ cold dark matter (ΛCDM) model. For a large class of our models, the accelerated expansion is transient with a nontrivial dependence on the model parameters. All models with wX>−1 will eventually contract and we derive an analytical expression for the scale factor a(t) in the neighborhood of its maximal value. We find also the scale factor for models ending in a Big Rip in the regime where dustlike matter density is negligible compared to λ. We address further the viability of such models, in particular when a high H0 is taken into account. While we find no decisive evidence for a nonzero λ, the best models are obtained with a phantom behavior on redshifts z≳1 with a higher evidence for nonzero λ. An observed value for h substantially higher than 0.70 would be a decisive test of their viability.

Ref HAL: hal-03129450_v1
Ref Arxiv: 2101.08240
Ref INSPIRE: 1842071
DOI: 10.1103/PhysRevD.104.034003
Ref. & Cit.: NASA ADS
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We apply the renormalization group optimized perturbation theory (RGOPT) to evaluate the quark contribution to the QCD pressure at finite temperatures and baryonic densities, at next-to-leading order (NLO). Our results are compared to NLO and state-of-the-art higher orders of standard perturbative QCD (pQCD) and hard thermal loop perturbation theory (HTLpt). The RGOPT provides an all order resummed pressure in a well-defined approximation, exhibiting a drastically better remnant renormalization scale dependence than pQCD, thanks to built-in renormalization group invariance consistency. At NLO, upon simply adding to the RGOPT-resummed quark contributions the purely perturbative NLO glue contribution, our results show a remarkable agreement with ab initio lattice simulation data for temperatures $0.25\lesssim T\lesssim 1\mathrm{GeV}$, with a remnant scale dependence drastically reduced as compared to HTLpt.

Ref HAL: hal-03115871_v1
Ref Arxiv: 2101.02124
Ref INSPIRE: 1839547
DOI: 10.1103/PhysRevD.104.L031502
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé:

The quark contribution to the QCD pressure, $P_q$, is evaluated up to next-to-leading order (NLO) within the renormalization group optimized perturbation theory (RGOPT) resummation approach. To evaluate the complete QCD pressure we simply add the perturbative NLO contribution from massless gluons to the resummed $P_q$. Despite this unsophisticated approximation our results for $P=P_q+P_g$ at the central scale $M\sim 2\pi T$ show a remarkable agreement with lattice predictions for $0.25\lesssim T\lesssim 1\mathrm{GeV}$. We also show that by being imbued with RG properties, the RGOPT produces a drastic reduction of the embarrassing remnant scale dependence that plagues both standard thermal perturbative QCD and hard thermal loop perturbation theory applications.

Ref HAL: hal-03087658_v1
Ref Arxiv: 2012.13947
Ref INSPIRE: 1838400
DOI: 10.1103/PhysRevD.103.115006
WoS: WOS:000661786800005
Ref. & Cit.: NASA ADS
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Tree-level dynamical stability of scalar field potentials in renormalizable theories can in principle be expressed in terms of positivity conditions on quartic polynomial structures. However, these conditions cannot always be cast in a fully analytical resolved form, involving only the couplings and being valid for all field directions. In this paper we consider such forms in three physically motivated models involving SU (2) triplet scalar fields: the Type-II seesaw model, the Georgi-Machacek model, and a generalized two-triplet model. A detailed analysis of the latter model allows to establish the full set of necessary and sufficient boundedness from below conditions. These can serve as a guide, together with unitarity and vacuum structure constraints, for consistent phenomenological (tree-level) studies. They also provide a seed for improved loop-level conditions, and encompass in particular the leading ones for the more specific Georgi-Machacek case. Incidentally, we present complete proofs of various properties and also derive general positivity conditions on quartic polynomials that are equivalent but much simpler than the ones used in the literature.

Ref HAL: hal-03047633_v1
Ref Arxiv: 2011.07049
Ref INSPIRE: 1830179
DOI: 10.1103/PhysRevD.103.046009
Ref. & Cit.: NASA ADS
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We identify a parametrically light dilaton by studying the perturbations of metastable vacua along a branch of regular supergravity backgrounds that are dual to four-dimensional confining field theories. The branch includes also stable and unstable solutions. The former encompass, as a special case, the geometry proposed by Witten as a holographic model of confinement. The latter approach a supersymmetric solution, by enhancing a condensate in the dual field theory. A phase transition separates the space of stable backgrounds from the metastable ones. In proximity of the phase transition, one of the lightest scalar states inherits some of the properties of the dilaton, despite not being particularly light.

Ref HAL: hal-03022688_v1
Ref Arxiv: 2011.01517
Ref INSPIRE: 1827879
DOI: 10.1103/PhysRevD.103.063509
Ref. & Cit.: NASA ADS
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We consider Horndeski modified gravity models obeying stability, velocity of gravitational waves cT equals c and quasistatic approximation on subhorizon scales. We assume further a Lambda cold dark matter background expansion and a monotonic evolution on the cosmic background of the α functions as αi=αi0as where i=M, B, a is the scale factor and αi0 (αM0,αB0), s are arbitrary parameters. We show that the growth and lensing reduced (dimensionless) gravitational couplings μ≡Ggrowth/G, Σ≡Glensing/G exhibit the following generic properties today: Σ0<1 for all viable parameters, μ0<1 (weak gravity today) is favored for small s while μ0>1 is favored for large s. We establish also the relation μ≥Σ at all times. Taking into account the fσ8 and EG data we constrain the parameter s to satisfy s≲2. Hence these data select essentially the weak gravity regime today (μ0<1) when s<2, while μ0>1 subsists only marginally for s≈2. At least the interval 0.5≲s≲2 would be ruled out in the absence of screening. We consider further the growth index γ(z) and identify the (αM0,αB0,s) parameter region that corresponds to specific signs of the differences γ0-γ0ΛCDM, and γ1-γ1ΛCDM, where γ0≡γ|z=0 and γ1≡dγdz|z=0. In this way important information is gained on the past evolution of μ. We obtain in particular the signature γ0>γ0ΛCDM for s<2 in the selected weak gravity region.

Ref HAL: hal-02930775_v1
Ref Arxiv: 2009.01172
DOI: 10.1007/JHEP01(2021)147
Ref. & Cit.: NASA ADS
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Extending recent results in ${\cal N}=2$ string compactifications, we propose that the holomorphic anomaly equation satisfied by the modular completions of the generating functions of refined BPS indices has a universal structure independent of the number ${\cal N}$ of supersymmetries. We show that this equation allows to recover all known results about modularity (under $SL(2,\mathbb{Z})$ duality group) of BPS states in ${\cal N}=4$ string theory. In particular, we reproduce the holomorphic anomaly characterizing the mock modular behavior of quarter-BPS dyons and generalize it to the case of non-trivial torsion invariant.