Primordial gravitational waves and the H0 -tension problem

Abstract

We analyze the H 0 -tension problem in the context of models of the early universe that predict a blue tilted spectrum of primordial gravitational waves (GWs), which is a positive value of the tensor tilt n T . By considering the GW's contribution, N GW eff , to the effective number of relativistic degrees of freedom, N eff , and assuming standard particle physics, we discuss the effects of N GW eff on the background expansion, especially the constraints on the Hubble parameter H 0 . We analyze three scenarios that take into account the contribution of N GW eff using recent data of cosmic microwave background, baryon acoustic oscillation, the latest measurement of the local expansion rate, along with the LIGO constraints on the tensor to scalar ratio, r, and the tensor index. For the models explored, we show that an additional contribution from the primordial GW's background to N eff does not solve but alleviates the current H 0 -tension problem.The contribution of N GW eff to the radiation content of the universe also affects the predictions of the primordial nucleosynthesis (BBN) [31,32].

Einstein, Planck and Vera Rubin: Relevant Encounters Between the Cosmological and the Quantum Worlds

“…including new physics in the ΛCDM theory to obtain changes in observational predictions, were explored to solve the H 0 tension. Among the proposals, we can mention the inclusion of extra relativistic species at recombination [18][19][20][21][22] and the dynamical interaction between dark matter and dark energy [23][24][25], as well as the investigation of the cosmological inflationary context [26]. Indeed, all these sectors can modify the value of the current expansion rate of the Universe.…”

Stability analysis for cosmological models in f(T, B) gravity

“…To follow the constraint of the system in Eqs. (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23), we need to write f T as a dynamical variable or write it in terms of the described variables. This can be done by considering a specific form of f (T, B) as we will show in Sect.…”

“…At its core, the CDM model was convinced to describe Hubble data but the so-called H 0 tension problem calls this into question where the observational discrepancy between model independent measurements [12,13] and predicted [14,15] a e-mail: geovanny.rave@ciencias.unam.mx b e-mail: celia.escamilla@nucleares.unam.mx c e-mail: jackson.said@um.edu.mt (corresponding author) values of H 0 from the early-Universe appears to be growing [16]. While measurements from the tip of the red giant branch (TRGB, Carnegie-Chicago Hubble Program) point to a lower H 0 tension, the issue may ultimately be resolved by future observations which may involve more exotic measuring techniques such as the use of gravitational wave astronomy [17,18] with the LISA mission [19,20]. However, it may also be the case that physics beyond general relativity (GR) are at play here.…”

Looking for interactions in the cosmological dark sector

“…Currently, one of the main arguments is that such discrepancies may be an indication of new physics beyond ΛCDM, and many analyses have investigated alternative scenarios that could reconcile the data sets. Attempts to solve the H 0 -tension problem for instance include extensions of the standard model, such as the existence of new relativistic particles [6,7], early dark energy [8], primordial gravitational waves [9], small spatial curvature [10], among others (see also [11,12] and references therein). In general, it is not straightforward to reconcile both the H 0 and σ 8 discrepancies in the same theoretical framework (see e.g.…”