Leading Logs in QCD Axion Effective Field Theory
TL;DR: In this article, the authors examine the adequacy of using such a naive EFT approach to study loop processes by comparing EFT calculations with ones performed in complete QCD axion models.
Abstract: The axion is much lighter than all other degrees of freedom introduced by the Peccei-Quinn mechanism to solve the strong CP problem. It is therefore natural to use an effective field theory (EFT) to describe its interactions. Loop processes calculated in the EFT may, however, explicitly depend on the ultraviolet cutoff. In general the UV cutoff is not uniquely defined, but the dimensionful couplings suggest to identify it with the Peccei-Quinn symmetry-breaking scale. An example are $K \rightarrow \pi + a$ decays that will soon be tested to improved precision in NA62 and KOTO and whose amplitude is dominated by the term logarithmically dependent on the cutoff. In this paper, we critically examine the adequacy of using such a naive EFT approach to study loop processes by comparing EFT calculations with ones performed in complete QCD axion models. In DFSZ models, for example, the cutoff is found to be set by additional Higgs degrees of freedom and to therefore be much closer to the electroweak scale than to the Peccei-Quinn scale. In fact, there are non-trivial requirements on axion models where the cutoff scale of loop processes is close to the Peccei-Quinn scale, such that the naive EFT result is reproduced. This suggests that the existence of a suitable UV embedding may impose restrictions on axion EFTs. We provide an explicit construction of a model with suitable fermion couplings and find promising prospects for NA62 and IAXO.
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TL;DR: In this paper , the authors investigated the phenomenology of an axion-like particle with flavor-changing couplings, and presented a comprehensive analysis of quark and lepton flavor changing observables within a general ALP effective field theory.
Abstract: Axions and axion-like particles (ALPs) are well-motivated low-energy relics of high-energy extensions of the Standard Model (SM). We investigate the phenomenology of an ALP with flavor-changing couplings, and present a comprehensive analysis of quark and lepton flavor-changing observables within a general ALP effective field theory. Observables studied include rare meson decays, flavor oscillations of neutral mesons, rare lepton decays, and dipole moments. We derive bounds on the general ALP couplings as a function of its mass, consistently taking into account the ALP lifetime and branching ratios. We further calculate quark flavor-changing effects that are unavoidably induced by running and matching between the new physics scale and the scale of the measurements. This allows us to derive bounds on benchmark ALP models in which only a single (flavorless or flavor-universal) ALP coupling to SM particles is present at the new physics scale, and in this context we highlight the complementarity and competitiveness of flavor bounds with constraints derived from collider, beam dump and astrophysical measurements. We find that searches for ALPs produced in meson decays provide some of the strongest constraints in the MeV-GeV mass range, even for the most flavorless of ALP models. Likewise, we discuss the interplay of flavor-conserving and flavor-violating couplings of the ALP to leptons, finding that constraints from lepton flavor-violating observables generally depend strongly on both. Additionally, we analyze whether an ALP can provide an explanation for various experimental anomalies including those observed in rare B-meson decays, measurements at the ATOMKI and KTeV experiments, and in the anomalous magnetic moments of the muon and the electron.
24 citations
DOI•
30 May 2022
TL;DR: In this article , it was shown that axion astrophobia keeps holding, albeit within fairly different parameter space regions, and the impact of renormalization group e ects on axion-mediated flavour violating observables was assessed.
Abstract: It has been recently pointed out that in certain axion models it is possible to suppress simultaneously both the axion couplings to nucleons and electrons, realising the so-called astrophobic axion scenarios, wherein the tight bounds from SN1987A and from stellar evolution of red giants and white dwarfs are greatly relaxed. So far, however, the conditions for realising astrophobia have only been set out in tree-level analyses. Here we study whether these conditions can still be consistently implemented once renormalization group e ff ects are included in the running of axion couplings. We find that axion astrophobia keeps holding, albeit within fairly di ff erent parameter space regions, and we provide transparent insights into this result. Given that astrophobic axion models generally feature flavour violating axion couplings, we also assess the impact of renormalization group e ff ects on axion-mediated flavour violating observables.
6 citations
TL;DR: In this paper , the authors propose a new approach to interpret the results of beam-dump experiments by separating the calculation of constraints and projected sensitivities into modelindependent and model-dependent parts.
Abstract: Proton beam dump experiments are among the most promising strategies to search for light and feebly interacting states such as axion-like particles (ALPs). The interpretation of these experiments is however complicated by the wide range of ALP models and the multitude of different production and decay channels that can induce observable signals. Here we propose a new approach to this problem by separating the calculation of constraints and projected sensitivities into model-independent and model-dependent parts. The former rely on extensive Monte Carlo simulations of ALP production and decays, as well as estimates of the detection efficiencies based on simplified detector geometries. Once these simulations have been performed and tabulated, the latter parts only require simple analytical rescalings that can be performed using the public code ALPINIST released together with this work. We illustrate this approach by considering several ALP models with couplings to Standard Model gauge bosons. For the case of ALPs coupled to gluons we show that the sensitivity of proton beam dump experiments can be extended significantly by considering hadronic ALP decays into three-body final states.
2 citations
TL;DR: In this paper , it was shown that axion astrophobia keeps holding, albeit within fairly different parameter space regions, and the impact of renormalization group effects on axion-mediated flavor-violating observables.
Abstract: It has been recently pointed out that in certain axion models it is possible to suppress simultaneously both the axion couplings to nucleons and electrons, realizing the so-called astrophobic axion scenarios, wherein the tight bounds from SN1987A and from stellar evolution of red giants and white dwarfs are greatly relaxed. So far, however, the conditions for realizing astrophobia have only been set out in tree-level analyses. Here we study whether these conditions can still be consistently implemented once renormalization group effects are included in the running of axion couplings. We find that axion astrophobia keeps holding, albeit within fairly different parameter space regions, and we provide analytical insights into this result. Given that astrophobic axion models generally feature flavor-violating axion couplings, we also assess the impact of renormalization group effects on axion-mediated flavor-violating observables.
2 citations
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TL;DR: In this paper, the authors give an explanation of the conservation of strong interactions which includes the effects of pseudoparticles, and they find it is a natural result for any theory where at least one flavor of fermion acquires its mass through a Yukawa coupling to a scalar field which has nonvanishing vacuum expectation value.
Abstract: We give an explanation of the $\mathrm{CP}$ conservation of strong interactions which includes the effects of pseudoparticles. We find it is a natural result for any theory where at least one flavor of fermion acquires its mass through a Yukawa coupling to a scalar field which has nonvanishing vacuum expectation value.
5,545 citations
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TL;DR: In this article, it was pointed out that a global U(1) symmetry, introduced in order to preserve the parity and time-reversal invariance of strong interactions despite the effects of instantons, would lead to a neutral pseudoscalar boson, the "axion", with mass roughly of order 100 keV to 1 MeV.
Abstract: It is pointed out that a global U(1) symmetry, that has been introduced in order to preserve the parity and time-reversal invariance of strong interactions despite the effects of instantons, would lead to a neutral pseudoscalar boson, the "axion," with mass roughly of order 100 keV to 1 MeV. Experimental implications are discussed.
4,138 citations
TL;DR: In this article, the color gauge theory of strong interactions without arbitrary adjustment of parameters is analyzed and several possibilities are identified, including one which would give a remarkable new kind of very light, long-lived pseudoscalar boson.
Abstract: The requirement that P and T be approximately conserved in the color gauge theory of strong interactions without arbitrary adjustment of parameters is analyzed. Several possibilities are identified, including one which would give a remarkable new kind of very light, long-lived pseudoscalar boson.
3,878 citations
TL;DR: In this article, the axial-vector vertex in spinor electrodynamics has anomalous properties which differ with those found by the formal manipulation of field equations, and the divergence of axial vector current is not the usual expression calculated from the field equations.
Abstract: Working within the framework of perturbation theory, we show that the axial-vector vertex in spinor electrodynamics has anomalous properties which disagree with those found by the formal manipulation of field equations. Specifically, because of the presence of closed-loop "triangle diagrams," the divergence of axial-vector current is not the usual expression calculated from the field equations, and the axial-vector current does not satisfy the usual Ward identity. One consequence is that, even after the external-line wave-function renormalizations are made, the axial-vector vertex is still divergent in fourth- (and higher-) order perturbation theory. A corollary is that the radiative corrections to ${\ensuremath{
u}}_{l}l$ elastic scattering in the local current-current theory diverge in fourth (and higher) order. A second consequence is that, in massless electrodynamics, despite the fact that the theory is invariant under ${\ensuremath{\gamma}}_{5}$ tranformations, the axial-vector current is not conserved. In an Appendix we demonstrate the uniqueness of the triangle diagrams, and discuss a possible connection between our results and the ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}2\ensuremath{\gamma}$ and $\ensuremath{\eta}\ensuremath{\rightarrow}2\ensuremath{\gamma}$ decays. In particular, we argue that as a result of triangle diagrams, the equations expressing partial conservation of axial-vector current (PCAC) for the neutral members of the axial-vector-current octet must be modified in a well-defined manner, which completely alters the PCAC predictions for the ${\ensuremath{\pi}}^{0}$ and the $\ensuremath{\eta}$ two-photon decays.
3,232 citations
TL;DR: In this article, the authors identify a new cosmological problem for models which solve the strong CP puzzle with an invisible axion, unrelated to the domain wall problem, and identify the energy density stored in the oscillations of the classical axion field does not dissipate rapidly; it exceeds the critical density needed to close the universe unless fa ⩽ 1012GeV wherefa is the axion decay constant.
2,557 citations