Probing new physics with gravity: a safe approach across different scales

Rafael Robson Lino Santos

Research output: ThesisPh.D. thesis

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This thesis investigates gravity at different energy scales to understand the fundamental properties and constituents of the observable dark universe. The thesis contains two main approaches. In the first approach, we explore the interplay of gravity-matter and the predictive power of asymptotically safe quantum gravity. Through functional renormalization group techniques, we investigate under which conditions some new physics models of the dark universe (axion-like particles and kinetic gravity braiding) and beyond Standard Model physics (cosmic strings) belong to the landscape of asymptotically safe quantum gravity. This landscape contains theories that are made ultraviolet complete by asymptotic safety and, at the same time, are compatible with phenomenology at infrared energy scales. We find that it is not straightforward to accommodate these theories in the landscape. In the second approach, we explore pulsar timing data to search for signals of new physics in the stochastic gravitational wave background. Through Bayesian inference, we investigate how well cosmological sources (inflation and scalar-induced gravitational waves) fit the NANOGrav 15 years data. We find that it is possible to explain the observed signal with these sources. Then, we derive bounds on the duration of reheating for the inflationary model, and on the dark matter abundance in the form of primordial black holes for the scalar-induced model. Even though the scalar-induced models provide very good fits to the signal, we find that significant portions of the viable parameter space are in tension with the dark matter bound if we neglect the effect of non-Gaussianities. Finally, we combine constraints on stable cosmic strings from pulsar timing searches with spontaneous symmetry breaking realizations in asymptotic safety, illustrating a scenario where physics at the Planck scale connects with gravitational-wave phenomenology.
Translated title of the contributionUndersøgelse af ny fysik med tyngdekraften: en sikker tilgang på tværs af forskellige skalaer
Original languageEnglish
Awarding Institution
  • University of Southern Denmark
  • Eichhorn, Astrid, Principal supervisor
Date of defence11. Oct 2023
Publication statusPublished - 7. Dec 2023


  • asymptotic safety
  • quantum gravity
  • gravitational waves
  • new physics
  • PTA searches
  • cosmology
  • dark matter


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  • From quantum gravity to gravitational waves through cosmic strings

    Eichhorn, A., Santos, R. R. L. D. & Miqueleto, J. L., Jan 2024, In: Physical Review D. 109, 2, 22 p., 026013.

    Research output: Contribution to journalJournal articleResearchpeer-review

    Open Access
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  • Shift-symmetric Horndeski gravity in the asymptotic-safety paradigm

    Eichhorn, A., Lino dos Santos, R. R. & Wagner, F., 1. Feb 2023, In: Journal of Cosmology and Astroparticle Physics. 2023, 2, 37 p., 052.

    Research output: Contribution to journalJournal articleResearchpeer-review

    Open Access
    56 Downloads (Pure)
  • The NANOGrav 15yr Data Set: Search for Signals from New Physics

    Afzal, A., Agazie, G., Anumarlapudi, A., Archibald, A. M., Arzoumanian, Z., Baker, P. T., Bécsy, B., Blanco-Pillado, J. J., Blecha, L., Boddy, K. K., Brazier, A., Brook, P. R., Burke-Spolaor, S., Burnette, R., Case, R., Charisi, M., Chatterjee, S., Chatziioannou, K., Cheeseboro, B. D. & Chen, S. & 103 others, Cohen, T., Cordes, J. M., Cornish, N. J., Crawford, F., Cromartie, H. T., Crowter, K., Cutler, C. J., DeCesar, M. E., DeGan, D., Demorest, P. B., Deng, H., Dolch, T., Drachler, B., von Eckardstein, R., Ferrara, E. C., Fiore, W., Fonseca, E., Freedman, G. E., Garver-Daniels, N., Gentile, P. A., Gersbach, K. A., Glaser, J., Good, D. C., Guertin, L., Gültekin, K., Hazboun, J. S., Hourihane, S., Islo, K., Jennings, R. J., Johnson, A. D., Jones, M. L., Kaiser, A. R., Kelley, L. Z., Kerr, M., Key, J. S., Laal, N., Lam, M. T., Kaplan, D. L., Lazio, J. T. W., Lee, V. S. H., Lewandowska, N., Lino dos Santos, R. R., Littenberg, T. B., Lamb, W. G., Liu, T., Lorimer, D. R., Luo, J., Lynch, R. S., Ma, C. P., McEwen, A., McKee, J. W., Madison, D. R., McLaughlin, M. A., McMann, N., Meyers, B. W., Meyers, P. M., Mingarelli, C. M. F., Mitridate, A., Nay, J., Natarajan, P., Ng, C., Nice, D. J., Ocker, S. K., Olum, K. D., Pennucci, T. T., Perera, B. B. P., Petrov, P., Pol, N. S., Radovan, H. A., Ransom, S. M., Ray, P. S., Romano, J. D., Sardesai, S. C., Schmiedekamp, A., Schmiedekamp, C., Schmitz, K., Schröder, T., Schult, L., Shapiro-Albert, B. J., Siemens, X., Simon, J., Siwek, M. S., Stairs, I. H., Stinebring, D. R., Stovall, K., Stratmann, P., Sun, J. P., Susobhanan, A., Swiggum, J. K., Taylor, J., Taylor, S. R., Trickle, T., Turner, J. E., Vallisneri, M., Unal, C., Verma, S., Vigeland, S. J., Wahl, H. M., Wang, Q., Witt, C. A., Wright, D., Young, O. & Zurek, K. M., 1. Jul 2023, In: Astrophysical Journal Letters. 951, 1, 56 p., L11.

    Research output: Contribution to journalJournal articleResearchpeer-review

    Open Access
    18 Downloads (Pure)

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