TY - JOUR

T1 - Spinors, Inflation, and Non-Singular Cyclic Cosmologies

AU - Armendáriz-Picón, C.

AU - Greene, Patrick B.

N1 - Funding Information:
It is a pleasure to thank Sean Carroll, Hsin-Chia Cheng, Paolo Gondonlo, Chris Hill, Slava Mukhanov, Kazumi Okuyama, Leonard Parker, and Glenn Starkman for useful and stimulating remarks and discussions. We especially thank Lev Kofman for useful comments. CAP was supported by the U.S. DoE grant DE-FG02-90ER40560. PBG was supported by the DOE and NASA grant NAG 5-10842 at Fermilab.

PY - 2003/9

Y1 - 2003/9

N2 - We consider toy cosmological models in which a classical, homogeneous, spinor field provides a dominant or sub-dominant contribution to the energy-momentum tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a field were to exist, appropriate choices of the spin or self-interaction would generate a rich variety of behaviors, quite different from their widely studied scalar field counterparts. We first discuss solutions that incorporate a stage of cosmic inflation and estimate the primordial spectrum of density perturbations seeded during such a stage. Inflation driven by a spinor field turns out to be unappealing as it leads to a blue spectrum of perturbations and requires considerable fine-tuning of parameters. We next find that, for simple, quartic spinor self-interactions, non-singular cyclic cosmologies exist with reasonable parameter choices. These solutions might eventually be incorporated into a successful past- and future-eternal cosmological model free of singularities. In an Appendix, we discuss the classical treatment of spinors and argue that certain quantum systems might be approximated in terms of such fields.

AB - We consider toy cosmological models in which a classical, homogeneous, spinor field provides a dominant or sub-dominant contribution to the energy-momentum tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a field were to exist, appropriate choices of the spin or self-interaction would generate a rich variety of behaviors, quite different from their widely studied scalar field counterparts. We first discuss solutions that incorporate a stage of cosmic inflation and estimate the primordial spectrum of density perturbations seeded during such a stage. Inflation driven by a spinor field turns out to be unappealing as it leads to a blue spectrum of perturbations and requires considerable fine-tuning of parameters. We next find that, for simple, quartic spinor self-interactions, non-singular cyclic cosmologies exist with reasonable parameter choices. These solutions might eventually be incorporated into a successful past- and future-eternal cosmological model free of singularities. In an Appendix, we discuss the classical treatment of spinors and argue that certain quantum systems might be approximated in terms of such fields.

KW - Cosmology

KW - Inflation

KW - Spinor field

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U2 - 10.1023/A:1025783118888

DO - 10.1023/A:1025783118888

M3 - Article

AN - SCOPUS:0346498037

VL - 35

SP - 1637

EP - 1658

JO - General Relativity and Gravitation

JF - General Relativity and Gravitation

SN - 0001-7701

IS - 9

ER -