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Grant support

We thank Asher Berlin, Sam McDermott for helpful conversations. Fermilab is operated by Fermi Research Alliance, LLC, under Contract No. DE-AC02-07CH11359 with the US Department of Energy. This project has received funding/support from the European Unions Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreements Elusives ITN No. 674896 and InvisiblesPlus RISE No. 690575. The work of MP was supported by the Spanish Agencia Estatal de Investigacion through the grants FPA2015-65929-P (MINECO/FEDER, UE), IFT Centro de Excelencia Severo Ochoa SEV-2016-0597, and Red Consolider MultiDark FPA2017-90566-REDC. ME is supported by the European Research Council under the European Union's Horizon 2020 program (ERC Grant Agreement No 648680 DARKHORIZONS). ME and MP acknowledge the Fermilab Theory and Astro groups for their hospitality when this project was initiated.

Analysis of institutional authors

Pierre, MathiasAuthor

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Article

Cosmology with a very light L - L gauge boson

Publicated to:Journal Of High Energy Physics. (3): - 2019-01-01 (3), DOI: 10.1007/JHEP03(2019)071

Authors: Escudero, Miguel; Hooper, Dan; Krnjaic, Gordan; Pierre, Mathias;

Affiliations

Univ Valencia, CSIC, Inst Fis Corpuscular IFIC, Valencia, Spain. - Author

Abstract

In this paper, we explore in detail the cosmological implications of an abelian L - L gauge extension of the Standard Model featuring a light and weakly coupled Z. Such a scenario is motivated by the longstanding approximate to 4 sigma discrepancy between the measured and predicted values of the muon's anomalous magnetic moment, (g - 2), as well as the tension between late and early time determinations of the Hubble constant. If sufficiently light, the Z population will decay to neutrinos, increasing the overall energy density of radiation and altering the expansion history of the early universe. We identify two distinct regions of parameter space in this model in which the Hubble tension can be significantly relaxed. The first of these is the previously identified region in which a approximate to 10 - 20 MeV Z reaches equilibrium in the early universe and then decays, heating the neutrino population and delaying the process of neutrino decoupling. For a coupling of g (-) similar or equal to (3 - 8) x 10(-4), such a particle can also explain the observed (g - 2) anomaly. In the second region, the Z is very light (mZ approximate to 1eV to MeV) and very weakly coupled (g (-) approximate to 10(-13) to 10(-9)). In this case, the Z population is produced through freeze-in, and decays to neutrinos after neutrino decoupling. Across large regions of parameter space, we predict a contribution to the energy density of radiation that can appreciably relax the reported Hubble tension, N-eff similar or equal to 0.2.

Keywords

Beyond standard modelCosmology of theories beyond the smL-muNeutrino physicsNeutrinos

Quality index

Bibliometric impact. Analysis of the contribution and dissemination channel

The work has been published in the journal Journal Of High Energy Physics due to its progression and the good impact it has achieved in recent years, according to the agency WoS (JCR), it has become a reference in its field. In the year of publication of the work, 2019, it was in position 4/29, thus managing to position itself as a Q1 (Primer Cuartil), in the category Physics, Particles & Fields.

This publication has been distinguished as a “Highly Cited Paper” by the agencies WoS (ESI, Clarivate) and ESI (Clarivate), meaning that it ranks within the top 1% of the most cited articles in its thematic field during the year of its publication. In terms of the observed impact of the contribution, this work is considered one of the most influential worldwide, as it is recognized as highly cited. (source consulted: ESI Nov 14, 2024)

And this is evidenced by the extremely high normalized impacts through some of the main indicators of this type, which, although dynamic over time and dependent on the set of average global citations at the time of calculation, already indicate that they are well above the average in different agencies:

  • Normalization of citations relative to the expected citation rate (ESI) by the Clarivate agency: 10.81 (source consulted: ESI Nov 14, 2024)
  • Field Citation Ratio (FCR) from Dimensions: 77.15 (source consulted: Dimensions Jun 2025)

Specifically, and according to different indexing agencies, this work has accumulated citations as of 2025-06-17, the following number of citations:

  • WoS: 168
  • Scopus: 169

Impact and social visibility

From the perspective of influence or social adoption, and based on metrics associated with mentions and interactions provided by agencies specializing in calculating the so-called "Alternative or Social Metrics," we can highlight as of 2025-06-17:

  • The use, from an academic perspective evidenced by the Altmetric agency indicator referring to aggregations made by the personal bibliographic manager Mendeley, gives us a total of: 20.
  • The use of this contribution in bookmarks, code forks, additions to favorite lists for recurrent reading, as well as general views, indicates that someone is using the publication as a basis for their current work. This may be a notable indicator of future more formal and academic citations. This claim is supported by the result of the "Capture" indicator, which yields a total of: 20 (PlumX).

With a more dissemination-oriented intent and targeting more general audiences, we can observe other more global scores such as:

  • The Total Score from Altmetric: 41.03.
  • The number of mentions on the social network X (formerly Twitter): 14 (Altmetric).
  • The number of mentions in news outlets: 2 (Altmetric).

It is essential to present evidence supporting full alignment with institutional principles and guidelines on Open Science and the Conservation and Dissemination of Intellectual Heritage. A clear example of this is:

Leadership analysis of institutional authors

There is a significant leadership presence as some of the institution’s authors appear as the first or last signer, detailed as follows: Last Author (PIERRE, MATHIAS GABRIEL MICHEL).