Spontaneous CP breaking in QCD and the axion potential: an effective Lagrangian approach

Vecchia, P. Di; Yankielowicz, Shimon; Veneziano, G.; Rossi, Giancarlo

doi:10.1007/jhep12(2017)104

Cited by 43 publications

(52 citation statements)

References 66 publications

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“…Modulo the (squared) Peccei-Quinn scale f 2 a , the axion mass squared is at all temperatures T given by the QCD topological susceptibility [11,43,[70][71][72]74] very accurately [75,76] (up to negligible corrections of the order (pion mass) 2 f 2 a ):…”

Section: Axion Mass From the Topological Susceptibility From Condensamentioning

confidence: 99%

Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the UA(1) Symmetry

2019

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The temperature (T) dependence of the axion mass is predicted for T ′ s up to ∼ 2.3× the chiral restoration temperature of QCD. The axion is related to the U A (1) anomaly. The squared axion mass m a (T) 2 is, modulo the presently undetermined scale of spontaneous breaking of Peccei-Quinn symmetry f a (squared), equal to QCD topological susceptibility χ(T) for all T. We obtain χ(T) by using quark condensates calculated in two effective Dyson-Schwinger models of nonperturbative QCD. They exhibit the correct chiral behavior, including the dynamical breaking of chiral symmetry and its restoration at high T. This is reflected in the U A (1) symmetry breaking and restoration through χ(T). In our previous studies, such χ(T) yields the T-dependence of the U A (1)-anomaly-influenced masses of η ′ and η mesons consistent with experiment. This in turn supports our prediction for the T-dependence of the axion mass. Another support is a rather good agreement with the pertinent lattice results. This agreement is not spoiled by our varying u and d quark mass parameters out of the isospin limit.2 of 23 mass-eigenstate basis, one diagonalizes the mass matrix, and the corresponding chiral transformation changes θ by arg det M. Hence, in the Standard Model the coefficient of the Q ∝ FF term is in fact. Therefore, to be precise, we change our notation toθ-term, L θ → Lθ.Since CP is not a symmetry of the Standard Model, there is no a priori reasonθ, which results from the contributions from both the strong and weak interactions, should vanish. And yet, the experimental bound on it is extremely low, θ < 10 −10 [9], and in fact consistent with zero. Therefore, the mystery of the vanishing strong CP violation is: why isθ so small?The most satisfactory answer till this very day has been provided by axions, even though the original variant has been ruled out [1]. In the meantime, they turned out to be very important also for cosmology, as promising candidates for dark matter-see from relatively recent references such as [10,11] to the earliest papers [12][13][14]. (For an example of a broader review of axion physics, see [15].) It is thus no wonder that ever since the original proposal of the axion mechanism [2-5] in 1977-1978, many theorists kept developing various ideas on this theoretically much needed object, trying to pinpoint the properties of this elusive particle and increase chances of finding it.However, to no avail. There have even been some speculations that the axion is hidden in plain sight, by being experimentally found, paradoxically, already years before it was conjectured theoretically: namely, that the axion should in fact be identified with the well-known η ′ meson with a minuscule admixture of a pseudoscalar composite of neutrinos [16]. Nevertheless, while an intimate relation between the axion and η ′ doubtlessly exists, reformulations of the axion theory, let alone so drastic ones, are in fact not needed to exploit this axion-η ′ relationship: thanks to the fact that both of their masses stem from the axial anomaly...

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Section: Axion Mass From the Topological Susceptibility From Condensamentioning

confidence: 99%

Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the UA(1) Symmetry

2019

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“…This vacuum structure has recently been clarified for finite N by the identification of a mixed discrete 't Hooft anomaly for T-symmetry and a 1-form center symmetry [5] (See also [6][7][8]). The presence of this anomaly, along with the assumption of a gapped spectrum, provides a more general argument for the spontaneous breaking of T-symmetry and the presence of degenerate vacua atθ ¼ π.…”

Section: Introductionmentioning

confidence: 99%

Domain wall moduli in softly-broken SQCD at θ¯=π

Ritz

Shukla

2018

Phys. Rev. D

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We analyze the moduli space dynamics of domain walls in SUðNÞ QCD atθ ¼ π, by softly breaking N ¼ 1 SQCD with sfermion mixing. In the supersymmetric limit, BPS domain walls between neighboring vacua are known to possess nontranslational flavor moduli that form a CP N−1 sigma model. For the simplest case with gauge group SUð2Þ and N f ¼ 2, we show that this sigma model also exhibits a Hopf term descending from the bulk Wess-Zumino term with a quantized coefficient. On soft-breaking of supersymmetry via sfermion mixing that preserves the flavor symmetry, these walls and their moduli-space dynamics survives whenθ ¼ π so that there are two degenerate vacua.

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“…It is discussed in Ref. [115] that in the SM at the zero temperature such breaking does not occur due to the small but non-degenerate up and down quark masses. Although at finite temperature a phase transition to the broken phase was argued to be possible, this possibility is currently disfavored by the recent lattice data.…”

Section: Discussionmentioning

confidence: 99%

QCD axion on hilltop by a phase shift of π.

Takahashi

Yin

2019

J. High Energ. Phys.

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We show that the initial misalignment angle of the QCD axion (or axion-like particles) can be set very close to π, if the QCD axion has a mixing with another heavy axion which induces the phase shift ≈ π after inflation. In the simplest case, the heavy axion plays the role of the inflaton, and we call such inflation as "πnflation." The basic idea was first proposed by Daido and the present authors in Ref.[1] in 2017 and more recently discussed in Ref. [2]. We show that the QCD axion with a decay constant f a 3 × 10 9 GeV can explain dark matter by the πnflation mechanism. A large fraction of the parameter region has an overlap with the projected sensitivity of ORGAN, MADMAX, TOORAD and IAXO. We also study implications for the effective neutrino species and isocurvature perturbations. The πnflation can provide an initial condition for the hilltop inflation in the axion landscape, and in a certain set-up, a chain of the hilltop inflation may take place. 1 arXiv:1908.06071v2 [hep-ph] 3 Oct 2019 5 The mass and kinetic mixings between the QCD axion and another axion were discussed in e.g. Refs. [41][42][43][44][45], where the level crossing between the two axions can reduce the axion abundance. The mixing can also induce the DM decay [1,46,47]. Also the mixing between axions plays an important role in inflation model building [48][49][50][51][52][53] 6 The axion isocurvature perturbations can be suppressed in this case [58]. See e.g. Refs. [14,26,[59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] for other scenarios to suppress the axion isocurvature.

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Spontaneous CP breaking in QCD and the axion potential: an effective Lagrangian approach

Cited by 43 publications

References 66 publications

Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the UA(1) Symmetry

Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the UA(1) Symmetry

Domain wall moduli in softly-broken SQCD at θ¯=π

QCD axion on hilltop by a phase shift of π.

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