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Author |
Giare, W.; Renzi, F.; Mena, O.; Di Valentino, E.; Melchiorri, A. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Is the Harrison-Zel'dovich spectrum coming back? ACT preference for n(s) similar to 1 and its discordance with Planck |
Type |
Journal Article |
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Year |
2023 |
Publication |
Monthly Notices of the Royal Astronomical Society |
Abbreviated Journal |
Mon. Not. Roy. Astron. Soc. |
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Volume |
521 |
Issue |
2 |
Pages |
2911-2918 |
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Keywords |
cosmological parameters; inflation; cosmology: observations; cosmology: theory |
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Abstract |
The Data Release 4 of the Atacama Cosmology Telescope (ACT) shows an agreement with an Harrison-Zel'dovich primordial spectrum (n(s) = 1.009 +/- 0.015), introducing a tension with a significance of 99.3 per cent Confidence Level (CL) with the results from the Planck satellite. The discrepancy on the value of the scalar spectral index is neither alleviated with the addition of large scale structure information nor with the low multipole polarization data. We discuss possible avenues to alleviate the tension relying on either neglecting polarization measurements from ACT or in extending different sectors of the theory. |
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Address |
[Giare, William] Ctr Nazl INFN Studi Avanzati, Galileo Galileo Inst Theoret Phys, Largo Enr Fermi 2, I-50125 Florence, Italy, Email: william.giare@gmail.com |
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Oxford Univ Press |
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English |
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ISSN |
0035-8711 |
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Notes |
WOS:000957248500013 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5510 |
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Permanent link to this record |
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Author |
Schiavone, T.; Montani, G.; Bombacigno, F. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
f(R) gravity in the Jordan frame as a paradigm for the Hubble tension |
Type |
Journal Article |
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Year |
2023 |
Publication |
Monthly Notices of the Royal Astronomical Society |
Abbreviated Journal |
Mon. Not. Roy. Astron. Soc. |
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Volume |
522 |
Issue |
1 |
Pages |
L72-L77 |
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Keywords |
supernovae: general; galaxies: distances and redshifts; cosmological parameters; dark energy; cosmology: theory |
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Abstract |
We analyse the f(R) gravity in the so-called Jordan frame, as implemented to the isotropic Universe dynamics. The goal of the present study is to show that according to recent data analyses of the supernovae Ia Pantheon sample, it is possible to account for an effective redshift dependence of the Hubble constant. This is achieved via the dynamics of a non-minimally coupled scalar field, as it emerges in the f(R) gravity. We face the question both from an analytical and purely numerical point of view, following the same technical paradigm. We arrive to establish that the expected decay of the Hubble constant with the redshift z is ensured by a form of the scalar field potential, which remains essentially constant for z less than or similar to 0.3, independently if this request is made a priori, as in the analytical approach, or obtained a posteriori, when the numerical procedure is addressed. Thus, we demonstrate that an f(R) dark energy model is able to account for an apparent variation of the Hubble constant due to the rescaling of the Einstein constant by the f(R) scalar mode. |
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[Schiavone, Tiziano] Univ Pisa, Dept Phys Fermi, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy, Email: tschiavone@fc.ul.pt |
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Oxford Univ Press |
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0035-8711 |
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WOS:001066034100015 |
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no |
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yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5672 |
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Permanent link to this record |
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Author |
Delhom, A.; Olmo, G.J.; Singh, P. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
A diffeomorphism invariant family of metric-affine actions for loop cosmologies |
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Journal Article |
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Year |
2023 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
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Volume |
06 |
Issue |
6 |
Pages |
059 - 21pp |
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Keywords |
quantum cosmology; modified gravity; cosmic singularity |
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Abstract |
In loop quantum cosmology (LQC) the big bang singularity is generically resolved by a big bounce. This feature holds even when modified quantization prescriptions of the Hamiltonian constraint are used such as in mLQC-I and mLQC-II. While the later describes an effective description qualitatively similar to that of standard LQC, the former describes an asymmetric evolution with an emergent Planckian de-Sitter pre-bounce phase even in the absence of a potential. We consider the potential relation of these canonically quantized non-singular models with effective actions based on a geometric description. We find a 3-parameter family of metric-affine f (R) theories which accurately approximate the effective dynamics of LQC and mLQC-II in all regimes and mLQC-I in the post-bounce phase. Two of the parameters are fixed by enforcing equivalence at the bounce, and the background evolution of the relevant observables can be fitted with only one free parameter. It is seen that the non-perturbative effects of these loop cosmologies are universally encoded by a logarithmic correction that only depends on the bounce curvature of the model. In addition, we find that the best fit value of the free parameter can be very approximately written in terms of fundamental parameters of the underlying quantum description for the three models. The values of the best fits can be written in terms of the bounce density in a simple manner, and the values for each model are related to one another by a proportionality relation involving only the Barbero-Immirzi parameter. |
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[Delhom, Adria; Singh, Parampreet] Louisiana State Univ, Dept Phys & Astron, Baton Rouge, LA 70803 USA, Email: adria.delhom@gmail.com; |
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Publisher |
IOP Publishing Ltd |
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English |
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1475-7516 |
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Notes |
WOS:001025410500003 |
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no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5583 |
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Permanent link to this record |
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Author |
Bordes, J.; Chan, H.M.; Tsou, S.T. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
A vacuum transition in the FSM with a possible new take on the horizon problem in cosmology |
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Journal Article |
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Year |
2023 |
Publication |
International Journal of Modern Physics A |
Abbreviated Journal |
Int. J. Mod. Phys. A |
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Volume |
38 |
Issue |
25 |
Pages |
2350124 - 32pp |
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Keywords |
Framed standard model; phase transition; early Universe; cosmology |
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Abstract |
The framed standard model (FSM), constructed to explain the empirical mass and mixing patterns (including CP phases) of quarks and leptons, in which it has done quite well, gives otherwise the same result as the standard model (SM) in almost all areas in particle physics where the SM has been successfully applied, except for a few specified deviations such as the W mass and the g-2 of muons, that is, just where experiment is showing departures from what SM predicts. It predicts further the existence of a hidden sector of particles some of which may function as dark matter. In this paper, we first note that the above results involve, surprisingly, the FSM undergoing a vacuum transition (VTR1) at a scale of around 17MeV, where the vacuum expectation values of the colour framons (framed vectors promoted into fields) which are all nonzero above that scale acquire some vanishing components below it. This implies that the metric pertaining to these vanishing components would vanish also. Important consequences should then ensue, but these occur mostly in the unknown hidden sector where empirical confirmation is hard at present to come by, but they give small reflections in the standard sector, some of which may have already been seen. However, one notes that if, going off at a tangent, one imagines colour to be embedded, Kaluza-Klein (KK) fashion, into a higher-dimensional space-time, then this VTR1 would cause 2 of the compactified dimensions to collapse. This might mean then that when the universe cooled to the corresponding temperature of 1011 K when it was about 10-3 s old, this VTR1 collapse would cause the three spatial dimensions of the universe to expand to compensate. The resultant expansion is estimated, using FSM parameters previously determined from particle physics, to be capable, when extrapolated backwards in time, of bringing the present universe back inside the then horizon, solving thus formally the horizon problem. Besides, VTR1 being a global phenomenon in the FSM, it would switch on and off automatically and simultaneously over all space, thus requiring seemingly no additional strategy for a graceful exit. However, this scenario has not been checked for consistency with other properties of the universe and is to be taken thus not as a candidate solution of the horizon problem but only as an observation from particle physics which might be of interest to cosmologists and experts in the early universe. For particle physicists also, it might serve as an indicator for how relevant this VTR1 can be, even if the KK assumption is not made. |
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Address |
[Bordes, Jose] Univ Valencia, Ctr Mixto CSIC, Dept Fis Teor, Calle Dr Moliner 50, E-46100 Burjassot, Valencia, Spain, Email: jose.m.bordes@uv.es; |
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World Scientific Publ Co Pte Ltd |
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English |
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0217-751x |
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Notes |
WOS:001099552500002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5803 |
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Permanent link to this record |
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Author |
Ghoshal, A.; Gouttenoire, Y.; Heurtier, L.; Simakachorn, P. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Primordial black hole archaeology with gravitational waves from cosmic strings |
Type |
Journal Article |
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Year |
2023 |
Publication |
Journal of High Energy Physics |
Abbreviated Journal |
J. High Energy Phys. |
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Volume |
08 |
Issue |
8 |
Pages |
196 - 43pp |
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Keywords |
Cosmology of Theories BSM; Early Universe Particle Physics; Phase Transitions in the Early Universe; Specific BSM Phenomenology |
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Abstract |
Light primordial black holes (PBHs) with masses smaller than 10(9) g (10(-24) M-circle dot) evaporate before the onset of Big-Bang nucleosynthesis, rendering their detection rather challenging. If efficiently produced, they may have dominated the universe energy density. We study how such an early matter-dominated era can be probed successfully using gravitational waves (GW) emitted by local and global cosmic strings. While previous studies showed that a matter era generates a single-step suppression of the GW spectrum, we instead find a double-step suppression for local-string GW whose spectral shape provides information on the duration of the matter era. The presence of the two steps in the GW spectrum originates from GW being produced through two events separated in time: loop formation and loop decay, taking place either before or after the matter era. The second step – called the knee – is a novel feature which is universal to any early matter-dominated era and is not only specific to PBHs. Detecting GWs from cosmic strings with LISA, ET, or BBO would set constraints on PBHs with masses between 10(6) and 10(9) g for local strings with tension G μ= 10(-11), and PBHs masses between 10(4) and 10(9) g for global strings with symmetry-breaking scale eta = 10(15) GeV. Effects from the spin of PBHs are discussed. |
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Address |
[Ghoshal, Anish] Univ Warsaw, Inst Theoret Phys, Fac Phys, Ul Pasteura 5, PL-02093 Warsaw, Poland, Email: anish.ghoshal@fuw.edu.pl; |
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Springer |
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English |
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1029-8479 |
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Notes |
WOS:001188227600001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5994 |
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Permanent link to this record |