TASI Lectures on the Strong CP Problem and Axions

Hook, Anson

doi:10.22323/1.333.0004

Cited by 80 publications

(66 citation statements)

References 141 publications

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“…On the other hand, largerK 1 requires the Yukawas during inflation to be larger than ∼ O(1). Thus we could not raise f a to be much above 10 15 GeV in the perturbative regime of our scenario. A more precise result for the allowed parameter space can be found in Fig.…”

Section: Dynamical Yukawa Couplingsmentioning

confidence: 89%

Dynamical axion misalignment with small instantons

Buen-Abad

Fan

2019

J. High Energ. Phys.

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We present a new mechanism to relax the initial misalignment angle of the QCD axion and raise the cosmological bound on the axion decay constant. The QCD axion receives a contribution from small UV instantons during inflation, which raises its mass to the inflationary Hubble scale. This makes the axion start rolling down its potential early on. In the scenario, the standard model Yukawa couplings of quarks are dynamical, being of order one during the inflationary era and reducing to their standard model values once it ends. This means that after inflation the contribution of the small instantons is suppressed, and the axion potential reduces to the standard one from the usual IR instantons. As a result, when the axion starts to oscillate again after inflation, the initial misalignment angle is suppressed due to the dynamics during inflation. While the general idea of dynamical axion misalignment has been discussed in the literature before, we present in detail the major bottleneck on the mismatching between the minima of the axion potentials during and after inflation, and how it is circumvented in our scenario via the Froggatt-Nielsen mechanism. Taking into account of all the constraints, we find that the axion decay constant could be raised to the GUT scale, 10 15 GeV, in our scenario.

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Section: Dynamical Yukawa Couplingsmentioning

confidence: 89%

Dynamical axion misalignment with small instantons

Buen-Abad

Fan

2019

J. High Energ. Phys.

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“…(3.22)) to account for arbitrary instanton locations inside SU (3). 5 The result is independent ofμ and we can therefore do the now trivial group integration in the results of Section 3.3. Note that the scalar action for SU (3) 2 , .…”

Section: Small Instanton Contributionsmentioning

confidence: 94%

“…Besides the QCD axion, axion-like particles (ALPs) are also ubiquitous in string theory, and can be used for many different purposes in BSM model building. For a pedagogic introduction to the axion and the strong CP problem, see for example [5].…”

Section: Introductionmentioning

confidence: 99%

UV sensitivity of the axion mass from instantons in partially broken gauge groups

Csáki

Ruhdorfer

Shirman

2020

J. High Energ. Phys.

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We examine the contribution of small instantons to the axion mass in various UV completions of QCD. We show that the reason behind the potential dominance of such contributions is the non-trivial embedding of QCD into the UV theory. The effects from instantons in the partially broken gauge group appear as "fractional instanton" corrections in the effective theory. These will exhibit unusual dependences on the various scales in the problem whenever the index of embedding is non-trivial. We present a full one-instanton calculation of the axion mass in the simplest product group models, carefully keeping track of numerical prefactors. Rather than using a 't Hooft operator approximation we directly evaluate the contributions to the vacuum bubble, automatically capturing the effects of closing up external fermion lines with Higgs loops. This approach is manifestly finite and removes the uncertainty associated with introducing a cutoff scale for the Higgs loops. We verify that the small instantons may dominate over the QCD contribution for very high breaking scales and at least three group factors.

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“…So what was once probably thought to be the standard theory explanation for DM now has strong additional competitors [55]. A major competitor is the axion, which not only can serve as DM [3,51], but was invented originally to solve the different problem of suppressing perceived strong sector sources of CP violations [49,35]. Much work still must go into finding the axion or closing its full window of parameter space.…”

Section: Four Mysteries Of the Cosmosmentioning

confidence: 99%

The Once and Present Standard Model of Elementary Particle Physics

Wells

2020

SpringerBriefs in Physics

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There are many theories that have resided these last fifty years within the hazy mist we have been calling the Standard Model (SM) of elementary particles. An attempt is made here to construct a coherent description of the SM today, because only precisely articulated theories can be targeted for annihilation, corroboration, and alteration. To this end it is useful to categorize the facts, mysteries and myths that together build a single conception of the SM. For example, it is argued that constructing a myth for how neutrinos obtain mass is useful for progress. We also advocate for interpreting the cosmological constant, dark matter, baryogenesis, and inflation as four "mysteries of the cosmos" that are indeterminate regarding new particles or interactions, despite a multitude of available particle explanations. Some history of the ever-changing SM is also presented to remind us that today's SM is not our parents' SM, nor will it likely be our children's SM.

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TASI Lectures on the Strong CP Problem and Axions

Cited by 80 publications

References 141 publications

Dynamical axion misalignment with small instantons

Dynamical axion misalignment with small instantons

UV sensitivity of the axion mass from instantons in partially broken gauge groups

The Once and Present Standard Model of Elementary Particle Physics

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