Ageeva Julia

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  PhD Student

I am mainly interested in the aspects of modern cosmology and gravity, namely the research of alternatives to inflation scenarios for early Universe. Inflation is indeed the strongest candidate however it has still unsolved problem called initial singularity. To get rid of the last, one can sew inflation with some earlier healthy non-singular epoch. Such epochs can be implemented in the framework of general scalar-tensor theory or so called Horndeski theory. Horndeski involves the scalar field whose lagrangian contains second derivatives of this field while maintaining the second-order nature of the equation of motion and thus erasing the Ostrogradsky instability. This property allows us to build non-singular cosmology as well. In particular, together with colleagues we were study stable (no gradient or ghost instabilities) genesis scenario. However It was shown that in such model one immediately obtains Planck mass running to zero (other words - strong coupling regime) for the very early Universe. However due to our analysis of third order action of all metric perturbations we found out that there is a full healthy region of lagrangian parameters; using the latter ones it is possible to build stable genesis without strong coupling regime in the very beginning of time. 

Selected publications:

Y. Ageeva, O. Evseev, O. Melichev and V. Rubakov. Horndeski Genesis: strong coupling and absence thereof, EPJ Web Conf. 191 (2018) 07010, [arXiv:1810.00465].

Publications affiliated with ITMP:

1. Ageeva, Y.; Petrov, P. (2023). "K-inflation: the legitimacy of classical treatment". arXiv: 2310.18402 [hep-th].
2. Ageeva, Y.; Petrov, P. (2022). "On the strong coupling problem in cosmologies with “strong gravity in the past". Modern Physics Letters A. 37 (2022) 26. arXiv: 2206.10646 [gr-qc]. doi: 10.1142/S0217732322501711.
3. Ageeva, Y.; Petrov, P. (2022). "Unitarity relation and unitarity bounds for scalars with different sound speeds". arXiv: 2206.03516 [hep-th].
4. Ageeva, Y., Petrov, P., Rubakov, V. (2022). "Generating cosmological perturbations at Horndeski bounce". Journal of High Energy Physics. 26 (2023). arXiv: 2207.04071 [hep-th]. doi: 10.1007/JHEP01(2023)026
5. Ageeva, Y.; Petrov, P.; Rubakov, V. (2021). "Non-singular cosmological models with strong gravity in the past". Physical Review D. 104 (2021) 063530. arXiv: 2104.13412 [hep-th]. doi: 10.1103/PhysRevD.104.063530.
6. Ageeva, Y.; Petrov, P.; Rubakov, V. (2020). "Horndeski genesis: consistency of classical theory". Journal of High Energy Physics. 107 (2020). arXiv: 2009.05071 [hep-th]. doi: 10.1007/JHEP12(2020)107.
7. Ageeva, Y.; Evseev, O.; Melichev, O.; Rubakov, V. (2020). "Toward evading the strong coupling problem in Horndeski Genesis". Physical Review D. 102 (2020) 2, 023519. arXiv: 2003.01202 [hep-th]. doi: 10.1103/PhysRevD.102.023519.