<p>We present a composite QCD axion model where the Peccei-Quinn symmetry emerges as a high-quality, accidental symmetry. The axion potential is only modified by eight-fermion, dimension-12 operators, which if present at the Planck scale, allow for axion dark matter from misalignment while solving the strong <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> problem. The model is an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>SU</mi><mo stretchy="false">(</mo><msub><mi>N</mi><mi>c</mi></msub><mo stretchy="false">)</mo></math> gauge theory with ten flavors where the Pati-Salam unified subgroup <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>SO</mi><mo stretchy="false">(</mo><mn>6</mn><mo stretchy="false">)</mo><mo>×</mo><mi>SO</mi><mo stretchy="false">(</mo><mn>4</mn><mo stretchy="false">)</mo><mo>⊂</mo><mi>SU</mi><mo stretchy="false">(</mo><mn>10</mn><msub><mo stretchy="false">)</mo><mi>L</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Sp</mi><mo stretchy="false">(</mo><mn>10</mn><mo stretchy="false">)</mo><mo>⊂</mo><mi>SU</mi><mo stretchy="false">(</mo><mn>10</mn><msub><mo stretchy="false">)</mo><mi>R</mi></msub></math> are weakly gauged. The dynamics breaks <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>SU</mi><mo stretchy="false">(</mo><mn>10</mn><msub><mo stretchy="false">)</mo><mi>L</mi></msub><mo>×</mo><mi>SU</mi><mo stretchy="false">(</mo><mn>10</mn><msub><mo stretchy="false">)</mo><mi>R</mi></msub><mo stretchy="false">→</mo><mi>SU</mi><mo stretchy="false">(</mo><mn>10</mn><msub><mo stretchy="false">)</mo><mi>V</mi></msub></math> and the weakly gauged groups to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>3</mn><mo stretchy="false">)</mo><mo>×</mo><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>2</mn><mo stretchy="false">)</mo><mo>⊃</mo><mi>SU</mi><mo stretchy="false">(</mo><mn>3</mn><msub><mo stretchy="false">)</mo><mi>c</mi></msub><mo>×</mo><mi>SU</mi><mo stretchy="false">(</mo><mn>2</mn><msub><mo stretchy="false">)</mo><mi>L</mi></msub><mo>×</mo><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mo stretchy="false">)</mo><mi>Y</mi></msub></math>, with the QCD axion identified as one of the Nambu-Goldstone bosons. This axion has a relatively large coupling to photons while a residual <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mover accent="true"><mi>θ</mi><mo stretchy="false">¯</mo></mover><mi>eff</mi></msub></math> may be just below the current limit on the neutron electric dipole moment. If the dimension-12 operators are present near the grand unified theory scale, they can cause domain wall networks to decay, allowing for axion dark matter even for the postinflationary scenario.</p>

United States

Tony Gherghetta

Japan

Hitoshi Murayama

Pablo Quílez

High-quality composite Pati-Salam axion

<p>We study the implications of noninvertible chiral symmetry in a four-dimensional U(1) gauge theory coupled to massless fermions with electromagnetic <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>L</mi><mo stretchy="false">(</mo><mn>2</mn><mo>,</mo><mi mathvariant="double-struck">Z</mi><mo stretchy="false">)</mo></math> duality. This is done by deriving the Adler-Bell-Jackiw anomaly of massless QED in the dual frame that is used to explicitly construct the symmetry defect operator as well as the conserved two-form symmetry current. As expected, the noninvertible chiral symmetry is covariant under the duality transformation. This has implications for understanding the nature of kinetic and topological terms in the dual frame and for axion electrodynamics. In particular, we show that to generate an axion potential from a dyon loop, the one-form magnetic symmetry must be explicitly broken by a mutually nonlocal charged state with nonzero pairwise helicity.</p>

Gongjun Choi

John Terning

Noninvertible chiral symmetry and axions under electromagnetic duality

We construct the thermal bounce solution in holographic models that describes first-order phase transitions between the deconfined and confined phases in strongly-coupled gauge theories. This new, periodic Euclidean solution represents transitions that occur via thermally-assisted tunneling and interpolates between the $\textit{O}$(4)-symmetric vacuum bubble at zero temperature and the high temperature $\textit{O}$(3)-symmetric critical bubble associated with classical thermal fluctuations. The exact thermal bounce solution can be used to obtain the bounce action at low temperatures which allows for a more accurate determination of vacuum decay rates, significantly improving previous estimates in holographic models. In particular, provided the phase transition is sufficiently supercooled, new predictions are obtained for the gravitational wave signal strength for critical temperatures ranging from the TeV scale up to 10 GeV, some of which are within reach of future gravitational wave detectors.

Arpon Paul

Canada

Andrey Shkerin

Holographic phase transitions via thermally-assisted tunneling

We use on-shell methods to compute all three-point interactions of massive spin-3/2 particles involving a graviton and particles of spin ≤ 1. By employing the massive spinor-helicity formalism we identify the interactions which have a smooth massless limit as expected from the superHiggs mechanism. These interactions are then used to on-shell construct four-point massive spin-3/2 amplitudes using an all-line transverse shift for the external momenta, which correctly reproduces the contact gravitino interactions in the $\textit{N}$ = 1 supergravity Lagrangian. The on-shell constructed four-point amplitudes are also used to derive well-known unitarity bounds in supergravity. In particular, by adding scalar and pseudoscalar interactions to construct the four-point massive spin-3/2 amplitudes that scale as $\textit{E}$ in the high-energy limit, we recover the on-shell Polonyi model with a Planck scale unitarity bound. These effective three-point interactions and on-shell recursion relations provide an alternative and simpler way to study the interactions of massive spin-3/2 particles without a Lagrangian or the use of Feynman diagrams.

Wenqi Ke

Effective interactions and on-shell recursion relation for massive spin 3/2

We propose a solution to the strong CP problem that specifically relies on massless quarks and has no light axion. The QCD color group SU(3) is embedded into a larger, simple gauge group (grand-color) where one of the massless, colored fermions enjoys an anomalous chiral symmetry, rendering the strong CP phase unphysical. The grand-color gauge group $\textit{G}$ is Higgsed down to SU(3) × $$ {G}_{c^{\prime }} $$ , after which $$ {G}_{c^{\prime }} $$ eventually confines at a lower scale, spontaneously breaking the chiral symmetry and generating a real, positive mass to the massless, colored fermion. Since the chiral symmetry has a $$ {G}_{c^{\prime }} $$ anomaly, there is no corresponding light Nambu-Goldstone boson. The anomalous chiral symmetry can be an accidental symmetry that arises from an exact discrete symmetry without introducing a domain wall problem. Potential experimental signals of our mechanism include vector-like quarks near the TeV scale, pseudo Nambu-Goldstone bosons below the 10 GeV scale, light dark matter decay, and primordial gravitational waves from the new strong dynamics.

Ravneet Bedi

Keisuke Harigaya

Solving the strong CP problem with massless grand-color quarks

We study the cosmological evolution of a light QCD axion and identify the parameter space to obtain the correct relic dark matter abundance. The axion potential is flattened at the origin, corresponding to the only minimum, while it is unsuppressed at π. These potential features arise by assuming a mirror sector with the strong CP phase   <math> <mover> <mi>θ</mi> <mo>¯</mo> </mover> </math>  $$ \overline{\theta} $$  shifted by π compared to the SM sector, which allows the mirror axion potential to be tuned against the usual QCD axion potential. Before the QCD phase transition, assuming the mirror sector is decoupled and much colder than the SM thermal bath, the mirror sector potential dominates, causing the axion to initially roll to a temporary minimum at π. However, after the QCD phase transition, the potential minimum changes, and the axion relaxes from the newly created “hilltop” near π to the CP-conserving minimum at the origin. As the axion adiabatically tracks this shift in the potential minimum through the QCD phase transition, with non-adiabatic evolution near π and 0, it alters the usual prediction of the dark matter abundance. Consequently, this “hilltop” misalignment mechanism opens new regions of axion parameter space, with the correct relic abundance while still solving the strong CP problem, that could be explored in future experiments.

Raymond Co

Zhen Liu

Kun-Feng Lyu

A light QCD axion with hilltop misalignment

Small instantons which increase the axion mass due to an appropriate modification of QCD at a UV scale ΛSI, can also enhance the effect of CP-violating operators to shift the axion potential minimum by an amount, θ ind, proportional to the flavorful couplings in the SMEFT. Since physical observables must be flavor basis independent, we construct a basis of determinant-like flavor invariants that arise from instanton calculations containing the effects of dimension-six CP-odd operators at the scale   . This new basis provides a more reliable estimate of the shift θ ind, that is severely constrained by neutron electric dipole moment experiments. In particular, for the case of four-quark, semi-leptonic and gluon dipole operators, these invariants are then used to provide improved limits on the ratio of scales    for different flavor scenarios. The CP-odd flavor invariants also provide a classification of the leading effects from Wilson coefficients, and as an example, we show that a semi-leptonic four-fermion operator is subdominant compared to the four-quark operators. More generally, the flavor invariants, together with an instanton NDA, can be used to more accurately estimate small instanton effects in the axion potential that arise from any SMEFT operator.

Germany

CERN

Christophe Grojean

Guilherme Guedes

Jonathan Kley

Pham Vuong

Small instanton-induced flavor invariants and the axion potential

We explore possible extensions of the Weak Gravity Conjecture (WGC) to scalar field theories. To avoid charged black hole remnants, the WGC requires the existence of a particle with a mass m ≤ gqM  P , with charge q and U(1) gauge coupling g, allowing the decay to shed the black hole charge. Although there is no obvious problem that arises in the absence of a U(1) charge, it has been postulated that gravity must remain the weakest force even when extended to scalar interactions. Quantifying this conjecture may be done by comparing scalar and gravitational amplitudes, or as we advocate here by comparing scattering cross sections. In theories with non-trivial field space geometries, by working out examples with perturbation theory around arbitrary field values and performing tadpole resummations, we argue that the conjecture must be applied only at extrema of the scalar potential (when expressed in locally canonical coordinates). We consider several toy models in the context of no-scale supergravity and also consider examples of inflationary models.

France

Emilian Dudas

Keith Olive

Sarunas Verner

Testing the scalar weak gravity conjecture in no-scale supergravity

We identify the QCD axion and right-handed (sterile) neutrinos as bound states of an SU(5) chiral gauge theory with Peccei-Quinn (PQ) symmetry arising as a global symmetry of the strong dynamics. The strong dynamics is assumed to spontaneously break the PQ symmetry, producing a high-quality axion and naturally generating Majorana masses for the right-handed neutrinos at the PQ scale. The composite sterile neutrinos can directly couple to the left-handed (active) neutrinos, realizing a standard see-saw mechanism. Alternatively, the sterile neutrinos can couple to the active neutrinos via a naturally small mass mixing with additional elementary states, leading to light sterile neutrino eigenstates. The SU(5) strong dynamics therefore provides a common origin for a high-quality QCD axion and sterile neutrinos.

Australia

Peter Cox

A common origin for the QCD axion and sterile neutrinos from SU(5) strong dynamics

Dark matter particles can form halos gravitationally bound to massive astrophysical objects. The Earth could have such a halo where depending on the particle mass, the halo either extends beyond the surface or is confined to the Earth’s interior. We consider the possibility that if dark matter particles are coupled to neutrinos, then neutrino oscillations can be used to probe an Earth dark matter halo. In particular, atmospheric neutrinos traversing the Earth can be sensitive to a small size, interior halo, inaccessible by other means. Depending on the halo mass and neutrino energy, constraints on the dark matter-neutrino couplings are obtained from the halo corrections to the neutrino oscillations.