Spontaneous baryogenesis from axions with generic couplings
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Springer
Received: June 17, 2020 Accepted: July 22, 2020 Published: August 20, 2020
Spontaneous baryogenesis from axions with generic couplings
a
DESY, Notkestraße 85, D-22607 Hamburg, Germany Theoretical Physics Department, CERN, 1 Esplanade des Particules, CH-1211 Geneva 23, Switzerland c Institute of Physics, Laboratory for Particle Physics and Cosmology, EPFL, CH-1015 Lausanne, Switzerland d Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan e Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan b
E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: Axion-like particles can source the baryon asymmetry of our Universe through spontaneous baryogenesis. Here we clarify that this is a generic outcome for essentially any coupling of an axion-like particle to the Standard Model, requiring only a non-zero velocity of the classical axion field while baryon or lepton number violating interactions are present in thermal bath. In particular, coupling the axions only to gluons is sufficient to generate a baryon asymmetry in the presence of electroweak sphalerons or the Weinberg operator. Deriving the transport equation for an arbitrary set of couplings of the axion-like particle, we provide a general framework in which these results can be obtained immediately. If all the operators involved are efficient, it suffices to solve an algebraic equation to obtain the final asymmetries. Otherwise one needs to solve a simple set of differential equations. This formalism clarifies some theoretical subtleties such as redundancies in the axion coupling to the Standard Model particles associated with a field rotation. We demonstrate how our formalism automatically evades potential pitfalls in the calculation of the final baryon asymmetry. Keywords: Cosmology of Theories beyond the SM, Thermal Field Theory ArXiv ePrint: 2006.03148
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP08(2020)096
JHEP08(2020)096
Valerie Domcke,a,b,c Yohei Ema,a Kyohei Mukaidaa and Masaki Yamadad,e
Contents 1 Introduction
1 4 4 7 10
3 Transport equation in the Standard Model 3.1 Standard Model interactions and charge vectors 3.2 Conserved quantities and decoupling
13 14 18
4 Spontaneous B + L-genesis before the electroweak phase transition 4.1 Basic properties of the transport equation 4.2 Equilibrium solution including the axion
21 21 24
5 Spontaneous B − L-genesis around the reheating epoch 5.1 Transport equation including the Weinberg operator 5.2 Equilibrium solution including the axion 5.3 Numerical results 5.4 Dependence on axion model parameters
26 26 28 30 34
6 Conclusion
36
A Definitions of symbols and indices
38
B Derivation of transport equation B.1 Transport equation without axion B.2 Source term from the axion
39 39 42
C Proof of the condition for vanishing backreaction
44
1
Introduction
The axion was introduced to solve the strong CP problem [1–4], but
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