A collider observable QCD axion

We study the formation and evolution of topological defects in an aligned axion model with multiple Peccei-Quinn scalars, where the QCD axion is realized by a certain combination of the axions with decay constants much smaller than the conventional PecceiQuinn breaking scale. When the underlying U(1) symmetries are spontaneously broken, the aligned structure in the axion field space exhibits itself as a complicated string-wall network in the real space. We find that the string-wall network likely survives until the QCD phase transition if the number of the Peccei-Quinn scalars is greater than two. The stringwall system collapses during the QCD phase transition, producing a significant amount of gravitational waves in the nano-Hz range at present. The typical decay constant is constrained to be below O(100) TeV by the pulsar timing observations, and the constraint will be improved by a factor of 2 in the future SKA observations.

Section: Jhep08(2016)044mentioning

confidence: 99%

Topological defects and nano-Hz gravitational waves in aligned axion models

Higaki

Jeong

Kitajima

et al. 2016

“…The behavior of the η can be studied in the framework of new exotic confining color groups, which are prevalent in model building to address the strong CP problem [20][21][22][23][24][25][26][27][28][29][30][31]. Heavy or visible axion models predominately utilize exotic color groups to alter the typical (m a , f a ) relationship [22][23][24][25][26][28][29][30][31][32][33]. There are generic features of chiral phase transitions in dynamical axion models that set them apart from general confining hidden sector models.…”

Section: Introductionmentioning

confidence: 99%

Dynamical axions and gravitational waves

Croon

Houtz

Sanz

2019

In this paper we explore the possibility of observable gravitational waves as a manifestation of the QCD axion dynamics. In particular, we focus on dynamical axion models which solve the strong CP problem, and include the confinement of a QCD-like gauge group at the TeV scale. We study the resulting chiral symmetry breaking phase transition for models with N F = 3 and N F = 4 light flavors using the linear sigma model. This model describes the scalar meson spectrum and its interactions, with the diagonal field ϕ as the order parameter. We find that the amplitude of the gravitational wave spectrum depends on the mass of the dynamical axion η via the ratio m η /m ϕ . The resulting spectra may be observed at future mid-range gravitational wave experiments such as AION/MAGIS, DECIGO, and BBO. Moreover, the TeV states can be searched for at colliders and their quantum numbers characterized, providing a unique connection between axion physics, gravitational waves and collider searches.

“…Interesting models implementing the mechanism of [12] were proposed in [14][15][16][17][18], applications to models of inflation were studied in [19]. Other approaches to modify the axion mass within QCD were proposed in [20][21][22][23] while in [24][25][26][27][28][29][30] the axion mass is raised by coupling it to a new confining gauge group.…”

Section: Introductionmentioning

confidence: 99%

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

Csáki

Ruhdorfer

Shirman

2020

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.