English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

If the refractive index of the tensor modes increases during a conventionalinflationary stage of expansion the relic graviton spectrum is tilted towardshigh frequencies. Two apparently diverse parametrizations of this effect areshown to be related by a rescaling of the four-dimensional metric through aconformal factor that involves the refractive index itself. Non-monotonicspectra with a maximum in the MHz region correspond to a limited variation ofthe refractive index terminating well before the end of inflation. Afterexploring a general approach encompassing the ones proposed so far, we estimatethe required sensitivity for the direct detection of the predictedgravitational radiation and demonstrate that the allowed regions of theparameter space are within reach for some of the planned detectors operatingeither in the audio band (like Ligo/Virgo and Kagra) or in the mHz band (likeLisa, Bbo and Decigo).

The propagating speed of relic gravitational waves and their refractive index during inflation