Fundamental Physics, the Swampland of Effective Field Theory and Early. . .
415
4 Conclusions and Discussion
In the context of effective field theories of matter coupled to Einstein gravity, a
number of early universe scenarios have been proposed which can explain current
observational data. Inflationary cosmology is one of them, but not the only one.
However, general considerations based on superstring theory indicate a tension
between fundamental physics and inflation. In fact, they indicate that any approach
based on effective field theory of matter coupled to Einstein gravity will break down
in the early universe, and that we need a radically different approach which takes
into account the new degrees of freedom and new symmetries which distinguish
string theories from point particles theories. I presented a toy model which takes
these aspects into account which indicates that the cosmology emerging from string
theory will be non-singular, and that it may not include any phase of inflation.
References
1. N. Aghanim, et al. [Planck Collaboration], Planck 2018 results. VI. Cosmological parameters.
arXiv:1807.06209 [astro-ph.CO]
2. R.A. Sunyaev, Y.B. Zeldovich, Small scale fluctuations of relic radiation. Astrophys. Space
Sci. 7, 3 (1970)
3. P.J.E. Peebles, J.T.Yu, Primeval adiabatic perturbation in an expanding universe. Astrophys. J.
162, 815 (1970). https://doi.org/10.1086/150713
4. A. Guth, The inflationary universe: a possible solution to the horizon and flatness problems.
Phys. Rev. D 23, 347 (1981); R. Brout, F. Englert, E. Gunzig, The creation of the universe as a
quantum phenomenon. Ann. Phys. 115, 78 (1978); A.A. Starobinsky, A new type of isotropic
cosmological models without singularity. Phys. Lett. B 91, 99 (1980); K. Sato, First order phase
transition of a vacuum and expansion of the universe. Mon. Not. Roy. Astron. Soc. 195, 467
(1981)
5. V. Mukhanov, G. Chibisov, Quantum fluctuation and nonsingular universe (in Russian). JETP
Lett. 33, 532 (1981). [Pisma Zh. Eksp. Teor. Fiz. 33, 549 (1981)]
6. R.H. Brandenberger, Cosmology of the very early universe. AIP Conf. Proc. 1268, 3 (2010).
https://doi.org/10.1063/1.3483879. [arXiv:1003.1745 [hep-th]]
7. W.H. Press, Spontaneous production of the Zel’dovich spectrum of cosmological fluctuations.
Phys. Scr. 21, 702 (1980). https://doi.org/10.1088/0031-8949/21/5/021
8. F. Finelli, R. Brandenberger, On the generation of a scale-invariant spectrum of adiabatic
fluctuations in cosmological models with a contracting phase. Phys. Rev. D 65, 103522 (2002).
[arXiv:hep-th/0112249]
9. M. Gasperini, G. Veneziano, Pre-big bang in string cosmology. Astropart. Phys. 1, 317 (1993).
https://doi.org/10.1016/0927-6505(93)90017-8. [hep-th/9211021]
10. J. Khoury, B.A. Ovrut, P.J. Steinhardt, N. Turok, The ekpyrotic universe: colliding branes and
the origin of the hot big bang. Phys. Rev. D 64, 123522 (2001). [hep-th/0103239]
11. D. Wands, Duality invariance of cosmological perturbation spectra. Phys. Rev. D 60, 023507
(1999). [arXiv:gr-qc/9809062]
12. J. Khoury, B.A. Ovrut, P.J. Steinhardt, N. Turok, Density perturbations in the ekpyrotic
scenario. Phys. Rev. D 66, 046005 (2002). https://doi.org/10.1103/PhysRevD.66.046005. [hepth/0109050]
13. E.J. Copeland, R. Easther, D. Wands, Vacuum fluctuations in axion - dilaton cosmologies.
Phys. Rev. D 56, 874 (1997). https://doi.org/10.1103/PhysRevD.56.874. [hep-th/9701082]
415
4 Conclusions and Discussion
In the context of effective field theories of matter coupled to Einstein gravity, a
number of early universe scenarios have been proposed which can explain current
observational data. Inflationary cosmology is one of them, but not the only one.
However, general considerations based on superstring theory indicate a tension
between fundamental physics and inflation. In fact, they indicate that any approach
based on effective field theory of matter coupled to Einstein gravity will break down
in the early universe, and that we need a radically different approach which takes
into account the new degrees of freedom and new symmetries which distinguish
string theories from point particles theories. I presented a toy model which takes
these aspects into account which indicates that the cosmology emerging from string
theory will be non-singular, and that it may not include any phase of inflation.
References
1. N. Aghanim, et al. [Planck Collaboration], Planck 2018 results. VI. Cosmological parameters.
arXiv:1807.06209 [astro-ph.CO]
2. R.A. Sunyaev, Y.B. Zeldovich, Small scale fluctuations of relic radiation. Astrophys. Space
Sci. 7, 3 (1970)
3. P.J.E. Peebles, J.T.Yu, Primeval adiabatic perturbation in an expanding universe. Astrophys. J.
162, 815 (1970). https://doi.org/10.1086/150713
4. A. Guth, The inflationary universe: a possible solution to the horizon and flatness problems.
Phys. Rev. D 23, 347 (1981); R. Brout, F. Englert, E. Gunzig, The creation of the universe as a
quantum phenomenon. Ann. Phys. 115, 78 (1978); A.A. Starobinsky, A new type of isotropic
cosmological models without singularity. Phys. Lett. B 91, 99 (1980); K. Sato, First order phase
transition of a vacuum and expansion of the universe. Mon. Not. Roy. Astron. Soc. 195, 467
(1981)
5. V. Mukhanov, G. Chibisov, Quantum fluctuation and nonsingular universe (in Russian). JETP
Lett. 33, 532 (1981). [Pisma Zh. Eksp. Teor. Fiz. 33, 549 (1981)]
6. R.H. Brandenberger, Cosmology of the very early universe. AIP Conf. Proc. 1268, 3 (2010).
https://doi.org/10.1063/1.3483879. [arXiv:1003.1745 [hep-th]]
7. W.H. Press, Spontaneous production of the Zel’dovich spectrum of cosmological fluctuations.
Phys. Scr. 21, 702 (1980). https://doi.org/10.1088/0031-8949/21/5/021
8. F. Finelli, R. Brandenberger, On the generation of a scale-invariant spectrum of adiabatic
fluctuations in cosmological models with a contracting phase. Phys. Rev. D 65, 103522 (2002).
[arXiv:hep-th/0112249]
9. M. Gasperini, G. Veneziano, Pre-big bang in string cosmology. Astropart. Phys. 1, 317 (1993).
https://doi.org/10.1016/0927-6505(93)90017-8. [hep-th/9211021]
10. J. Khoury, B.A. Ovrut, P.J. Steinhardt, N. Turok, The ekpyrotic universe: colliding branes and
the origin of the hot big bang. Phys. Rev. D 64, 123522 (2001). [hep-th/0103239]
11. D. Wands, Duality invariance of cosmological perturbation spectra. Phys. Rev. D 60, 023507
(1999). [arXiv:gr-qc/9809062]
12. J. Khoury, B.A. Ovrut, P.J. Steinhardt, N. Turok, Density perturbations in the ekpyrotic
scenario. Phys. Rev. D 66, 046005 (2002). https://doi.org/10.1103/PhysRevD.66.046005. [hepth/0109050]
13. E.J. Copeland, R. Easther, D. Wands, Vacuum fluctuations in axion - dilaton cosmologies.
Phys. Rev. D 56, 874 (1997). https://doi.org/10.1103/PhysRevD.56.874. [hep-th/9701082]