Axion misalignment driven to the hilltop

“…φ =φ(0) +φt, (A. 16) whereφ(0) =φ(t = 0). The assumption of neglecting higher derivatives is justified in the main text, see the discussion around Eq.…”

Section: A2 Small Non-zeroφ and Hmentioning

confidence: 99%

“…This effect is important only if the initial position of the axion field is tuned very close to the top of the barrier of the axion potential, at the level of ∼ 10 −7 . Such peculiar initial position was recently motivated by some inflation dynamics in [16] and by anthropic arguments in [17].…”

mentioning

confidence: 99%

Axion fragmentation

Fonseca

Morgante

Sato

et al. 2020

J. High Energ. Phys.

137

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We investigate the production of axion quanta during the early universe evolution of an axion-like field rolling down a wiggly potential. We compute the growth of quantum fluctuations and their back-reaction on the homogeneous zeromode. We evaluate the transfer of kinetic energy from the zero mode to the quantum fluctuations and the conditions to decelerate the axion zero-mode as a function of the Hubble rate, the slope of the potential, the size of the barriers and the initial field velocity. We discuss how these effects impact the relaxion mechanism. arXiv:1911.08472v1 [hep-ph] 19 Nov 2019 1 As this work was being completed, Ref.[15] appeared, which considers the production of axion quantum fluctuations during oscillations about the minimum of the potential, as in [14]. This effect is important only if the initial position of the axion field is tuned very close to the top of the barrier of the axion potential, at the level of ∼ 10 −7 . Such peculiar initial position was recently motivated by some inflation dynamics in [16] and by anthropic arguments in [17].

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“…Even when one requires that this explicit breaking not spoil the solution to the Strong CP problem in the present universe, the rotation can still be induced from such interactions in the early universe as we will describe. Another example is a larger QCD scale in the early universe [30][31][32][33], which can initiate the axion oscillation and, once the QCD scale becomes small enough, the axion begins to rotate.A fast rotation of the axion corresponds to a large PQ charge asymmetry. The PQ asymmetry is converted into chiral asymmetries of SM quarks via QCD sphaleron transitions.…”

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confidence: 99%

Axiogenesis

2020

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We propose a mechanism called axiogenesis where the cosmological excess of baryons over antibaryons is generated from the rotation of the QCD axion. The Peccei-Quinn (PQ) symmetry may be explicitly broken in the early universe, inducing the rotation of a PQ charged scalar field. The rotation corresponds to the asymmetry of the PQ charge, which is converted into the baryon asymmetry via QCD and electroweak sphaleron transitions. In the concrete model we explore, interesting phenomenology arises due to the prediction of a small decay constant and the connections with new physics at the LHC and future colliders and with axion dark matter.Introduction.-One of the goals of fundamental physics is to understand the origin of the Universe. For this purpose, the Standard Model (SM) of particle physics needs an extension to explain the cosmological excess of matter over antimatter. Mechanisms to generate the baryon asymmetry have been intensively studied in the literature under the name of baryogenesis [1][2][3][4][5][6][7][8].The SM also needs an extension to explain the smallness of CP violation in QCD [9] which on theoretical grounds is expected to be large [10]. This is known as the strong CP problem and can be elegantly solved by the Peccei-Quinn (PQ) mechanism [11,12]. The so-called the PQ symmetry is spontaneously broken to yield a pseudo Nambu-Goldstone boson, the axion [13,14]. The PQ symmetry is explicitly broken by the quantum effects of QCD of the Adler-Bell-Jeckiw type [15,16]. The quantum effects give a potential to the axion and drive the axion field value to the point where CP symmetry is restored, solving the strong CP problem. The axion is also a dark matter candidate [17][18][19], which makes the PQ mechanism even more attractive.We discover that when the PQ mechanism is introduced into the SM, the baryon (B) and lepton (L) asymmetries are generated in a wide class of models. We call the following baryogenesis scheme as axiogenesis, which in general includes two main ingredients: 1) an asymmetry of the PQ charge is generated in the early universe as a coherent rotation in the axion direction and 2) the PQ asymmetry is later transferred to the B + L asymmetry via the QCD and electroweak sphaleron transitions. We contrast axiogenesis with other existing baryogenesis models after we introduce a concrete example. (We may convert the B + L asymmetry into the B − L asymmetry by some B − L breaking interaction. The investigation of such a scenario will be considered in a future work [20].)The PQ symmetry is an approximate global symmetry which is explicitly broken by the QCD anomaly. Given that the symmetry is not exact, it is conceivable that the PQ symmetry is significantly broken in the early universe, and the rotation of the axion is induced. In fact, it is expected that quantum gravity does not allow for a global symmetry [21][22][23][24][25] and the PQ symmetry is at best understood as an accidental symmetry explicitly broken by higher dimensional operators [26][27][28][29]. Even when one requires that t...

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Axion misalignment driven to the hilltop

Abstract: The QCD axion serves as a well-motivated dark matter candidate and the misalignment mech-

Cited by 70 publications

References 87 publications

Misalignment & Co.: (pseudo-)scalar and vector dark matter with curvature couplings

Misalignment & Co.: (pseudo-)scalar and vector dark matter with curvature couplings

Axion fragmentation

Axiogenesis

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