Topology in full QCD at high temperature: a multicanonical approach

Bonati, Claudio; D’Elia, Massimo; Martinelli, G.; Negro, Francesco; Sanfilippo, Francesco; Todaro, Antonino

doi:10.1007/jhep11(2018)170

Cited by 76 publications

(81 citation statements)

References 126 publications

(159 reference statements)

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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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“…where n = 4 for the SM is obtained by the dilute instanton gas approximation (see the lattice simulations in Refs. [54][55][56][57][58], whose results indicate that n ranges from 3.0 to 3.7 depending on the temperature). The equation of motion and the energy density read where n = 0 is understood for f a 10 17 GeV as the axion mass reaches the zero-temperature value before the oscillation starts.…”

Section: Misalignment Mechanismmentioning

confidence: 96%

Axion misalignment driven to the bottom

González

Harigaya

2019

J. High Energ. Phys.

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Several theoretical motivations point to ultralight QCD axions with large decay constants f a O(10 16 -10 17 ) GeV, to which experimental proposals are dedicated. This regime is known to face the problem of overproduction of axion dark matter from the misalignment mechanism unless the misalignment angle θ mis is as small as O(10 −3 -10 −4 ), which is generally considered a finetuning problem. We investigate a dynamical explanation for a small θ mis . The axion mass arises from strong dynamics and may be sufficiently enhanced by early dynamics so as to overcome Hubble friction and drive the field value to the bottom of the potential long before the QCD phase transition. Together with an approximate CP symmetry in the theory, this minimum is very closely related to today's value and thus θ mis can automatically be well under unity. Owing to such efficient relaxation, the isocurvature perturbations are essentially damped. As an existence proof, using supersymmetric theories we illustrate that the Higgs coupling with the inflaton energy can successfully achieve this axion damping in a consistent inflationary cosmology.

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“…(2.4) and (2.5) assume the topological susceptibility of QCD given by the dilute instanton gas approximation (see the lattice results in Refs. [58][59][60][61][62]) but our results are insensitive to this uncertainty.…”

Section: Axion Misalignment and Early Relaxationmentioning

confidence: 99%