Peccei-Quinn Symmetry Breaking Scale Research Articles

Meso-inflationary QCD axion

We study the possibility that the axion Peccei-Quinn symmetry is spontaneously broken after the beginning of inflation. This scenario interpolates between preinflationary and postinflationary axion cosmology with significant phenomenological differences from both. Since the axion is not present at the early stages of inflation large inflationary fluctuations are produced only at scales not constrained by cosmic microwave background (CMB), avoiding the strongest isocurvature constraints. The energy density in isocurvature perturbations at short scales however can be comparable with the adiabatic contribution from misalignment. These large overdensities can lead to the formation of axion miniclusters and also to constraints from Lyman-$\ensuremath{\alpha}$ forest and future CMB spectral distortion measurements. If Peccei-Quinn symmetry is broken during the first O(25) $e$-foldings of inflation no axions are produced from the string network but contributions from the annihilation of domain walls can further boost the abundance. This scenario is minimally realized if the Hubble scale during inflation drops below the Peccei-Quinn symmetry breaking scale but other realizations are possible.

The minimal UV-induced effective QCD axion theory

The characteristic axion couplings could be generated via effective couplings between the Standard Model (SM) fermions to a pseudo-Goldstone from a high-scale U(1) Peccei–Quinn (PQ) symmetry breaking. Assuming that the UV-induced effective operators generate necessary couplings before the PQ symmetry breaking, and any low-scale couplings to the SM are restricted to the Yukawa sector, three minimal natural scenarios can be formulated, which provide a connection between the QCD axions and mediators at the GUT/string scales. We find that the PQ symmetry breaking scale could be about [Formula: see text] GeV, higher than the classical QCD dark matter axion window but possible if the anthropic window is considered. We also propose an experiment to probe such scenarios. If the dark matter axion is discovered, they might suggest that we live in an atypical Hubble volume.

Filtered asymmetric dark matter during the Peccei-Quinn phase transition

In this paper, we propose a bubble filtering-out mechanism for an asymmetric dark matter scenario during the Peccei-Quinn (PQ) phase transition. Based on a QCD axion model, extended by extra chiral neutrinos, we show that the PQ phase transition can be first order in the parameter space of the model and regarding the PQ symmetry breaking scale, the mechanism can generate PeV-scale heavy neutrinos as a dark matter candidate. Considering a CP-violating source, during the phase transition, discriminating between the neutrino and antineutrino number density, we find the observed dark matter relic abundance, such that the setup can be applied to the first order phase transition with different strengths. We then calculate effective couplings of the QCD axion addressing the strong CP problem within the model. We also study the energy density spectrum of gravitational waves generated from the first order phase transition and show that the signals can be detected by future ground-based detectors such as Einstein Telescope. In particular, for a visible heavy axion case of the model, it is shown that gravitational waves can be probed by DECIGO and BBO interferometers. Furthermore, we discuss the dark matter-standard model neutrino annihilation process as a source for the creation of PeV-scale neutrinos.

PeV gravitino, weak-scale Higgsino, and GeV axino in the Kachru-Kalosh-Linde-Trivedi setup

We realize high scale supersymmetry in the mirage mediation. The Higgs sector is extended with the Peccei-Quinn symmetry, and the higgsino mass term is generated by the Kim-Nilles mechanism. In particular, the Peccei-Quinn symmetry breaking scale naturally lies on the mirage messenger scale due to the mixed modulus-anomaly mediation with the gauge coupling unification. Consequently, the higgsino mass term is of order the weak scale while the gravitino mass is of PeV order. This hierarchy naturally leads to the correct electroweak symmetry breaking. The higgsinos are thus in the range accessible at future lepton colliders, while other sparticles are well-above the current LHC reach and consistent with the observed Higgs boson. The axino is dominantly produced from the modulus decay and accounts for the correct dark matter abundance.

Leading logs in QCD axion effective field theory

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+ → π+ + 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.

Gravitational waves from fundamental axion dynamics

A totally asymptotically free QCD axion model, where all couplings flow to zero in the infinite energy limit, was recently formulated. A very interesting feature of this fundamental theory is the ability to predict some low-energy observables, like the masses of the extra fermions and scalars. Here we find and investigate a region of the parameter space where the Peccei-Quinn (PQ) symmetry is broken quantum mechanically through the Coleman-Weinberg mechanism. This results in an even more predictive framework: the axion sector features only two independent parameters (the PQ symmetry breaking scale and the QCD gauge coupling). In particular, we show that the PQ phase transition is strongly first order and can produce gravitational waves within the reach of future detectors. The predictivity of the model leads to a rigid dependence of the phase transition (like its duration and the nucleation temperature) and the gravitational wave spectrum on the PQ symmetry breaking scale and the QCD gauge coupling.

Dirac neutrino from the breaking of Peccei-Quinn symmetry

We propose a model where Dirac neutrino mass is obtained from small vacuum expectation value (VEV) of neutrino-specific Higgs doublet without fine-tuning problem. The small VEV results from a seesaw-like formula with the high energy scale identified as the Peccei-Quinn (PQ) symmetry breaking scale. Axion can be introduced à la KSVZ or DFSZ. The model suggests neutrino mass, solution to the strong CP problem, and dark matter may be mutually interconnected.

Scaling Density of Axion Strings.

In the QCD axion dark matter scenario with postinflationary Peccei-Quinn symmetry breaking, the number density of axions, and hence the dark matter density, depends on the length of string per unit volume at cosmic time t, by convention written ζ/t^{2}. The expectation has been that the dimensionless parameter ζ tends to a constant ζ_{0}, a feature of a string network known as scaling. It has recently been claimed that in larger numerical simulations ζ shows a logarithmic increase with time, while theoretical modeling suggests an inverse logarithmic correction. Either case would result in a large enhancement of the string density at the QCD transition, and a substantial revision to the axion mass required for the axion to constitute all of the dark matter. With a set of new simulations of global strings, we compare the standard scaling (constant-ζ) model to the logarithmic growth and inverse-logarithmic correction models. In the standard scaling model, by fitting to linear growth in the mean string separation ξ=t/sqrt[ζ], we find ζ_{0}=1.19±0.20. We conclude that the apparent corrections to ζ are artifacts of the initial conditions, rather than a property of the scaling network. The residuals from the constant-ζ (linear ξ) fit also show no evidence for logarithmic growth, restoring confidence that numerical simulations can be simply extrapolated from the Peccei-Quinn symmetry-breaking scale to the QCD scale. Reanalysis of previous work on the axion number density suggests that recent estimates of the axion dark matter mass in the postinflationary symmetry-breaking scenario we study should be increased by about 50%.

Domain wall and isocurvature perturbation problems in a supersymmetric axion model

The axion causes two serious cosmological problems, domain wall and isocurvature perturbation problems. Linde pointed that the isocurvature perturbations are suppressed when the Peccei-Quinn (PQ) scalar field takes a large value $\sim M_{\text{pl}}$ (Planck scale) during inflation. In this case, however, the PQ field with large amplitude starts to oscillate after inflation and large fluctuations of the PQ field are produced through parametric resonance, which leads to the formation of domain walls. We consider a supersymmetric axion model and examine whether domain walls are formed by using lattice simulation. It is found that the domain wall problem does not appear in the SUSY axion model when the initial value of the PQ field is less than $10^{3}\times v$ where $v$ is the PQ symmetry breaking scale.

Radiative PQ breaking and the Higgs boson mass

The small and negative value of the Standard Model Higgs quartic coupling at high scales can be understood in terms of anthropic selection on a landscape where large and negative values are favored: most universes have a very short-lived electroweak vacuum and typical observers are in universes close to the corresponding metastability boundary. We provide a simple example of such a landscape with a Peccei-Quinn symmetry breaking scale generated through dimensional transmutation and supersymmetry softly broken at an intermediate scale. Large and negative contributions to the Higgs quartic are typically generated on integrating out the saxion field. Cancellations among these contributions are forced by the anthropic requirement of a sufficiently long-lived electroweak vacuum, determining the multiverse distribution for the Higgs quartic in a similar way to that of the cosmological constant. This leads to a statistical prediction of the Higgs boson mass that, for a wide range of parameters, yields the observed value within the 1σ statistical uncertainty of ∼ 5 GeV originating from the multiverse distribution. The strong CP problem is solved and single-component axion dark matter is predicted, with an abundance that can be understood from environmental selection. A more general setting for the Higgs mass prediction is discussed.

The quest for an intermediate-scale accidental axion and further ALPs

The recent detection of the cosmic microwave background polarimeter experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically excludes all plausible axion models where its decay constant is above 1013 GeV. Moreover, there are strong theoretical, astrophysical, and cosmological motivations for models involving, in addition to the axion, also axion-like particles (ALPs), with decay constants in the intermediate scale range, between 109 GeV and 1013 GeV. Here, we present a general analysis of models with an axion and further ALPs and derive bounds on the relative size of the axion and ALP photon (and electron) coupling. We discuss what we can learn from measurements of the axion and ALP photon couplings about the fundamental parameters of the underlying ultraviolet completion of the theory. For the latter we consider extensions of the Standard Model in which the axion and the ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global chiral U(1) (Peccei-Quinn (PQ)) symmetries, occurring accidentally as low energy remnants from exact discrete symmetries. In such models, the axion and the further ALP are protected from disastrous explicit symmetry breaking effects due to Planck-scale suppressed operators. The scenarios considered exploit heavy right handed neutrinos getting their mass via PQ symmetry breaking and thus explain the small mass of the active neutrinos via a seesaw relation between the electroweak and an intermediate PQ symmetry breaking scale. For a number of explicit models, we determine the parameters of the low-energy effective field theory describing the axion, the ALPs, and their interactions with photons and electrons, in terms of the input parameters, in particular the PQ symmetry breaking scales. We show that these models can accommodate simultaneously an axion dark matter candidate, an ALP explaining the anomalous transparency of the universe for γ-rays, and an ALP explaining the recently reported 3.55 keV gamma line from galaxies and clusters of galaxies, if the respective decay constants are of intermediate scale. Moreover, they do not suffer severely from the domain wall problem.

Search for 14.4 keV solar axions from M1 transition of 57Fe with CUORE crystals

We report the results of a search for axions from the 14.4 keV M1 transition from 57Fe in the core of the sun using the axio-electric effect in TeO2 bolometers. The detectors are 5 × 5 × 5 cm3 crystals operated at about 10 mK in a facility used to test bolometers for the CUORE experiment at the Laboratori Nazionali del Gran Sasso in Italy. An analysis of 43.65 kg⋅d of data was made using a newly developed low energy trigger which was optimized to reduce the energy threshold of the detector. An upper limit of 0.58 c⋅kg−1⋅d−1 is established at 95% C.L., which translates into lower bounds fA ⩾ 3.12 × 105 GeV 95% C.L. (DFSZ model) and fA ⩾ 2.41 × 104 GeV 95% C.L. (KSVZ model) on the Peccei-Quinn symmetry-breaking scale, for a value of S = 0.5 of the flavor-singlet axial vector matrix element. These bounds can be expressed in terms of axion masses as mA ⩽ 19.2 eV and mA ⩽ 250 eV at 95% C.L. in the DFSZ and KSVZ models respectively. Bounds are given also for the interval 0.35 ⩽ S ⩽ 0.55.

Probing axino LSP from diphoton events with large missing transverse energy

In a supersymmetry model with an axino as the lightest supersymmetric particle (LSP) and a Bino as the next LSP (NLSP), supersymmetric particle production ends up with including two Binos, followed by each Binoʼs decaying into a photon and an axino. Final states are diphoton with large missing energy. In a benchmark scenario, we have comprehensively studied the implication of γγ+E̸(T) data from the ALEPH, CDF II, ATLAS and CMS experiments. No excess over the standard model backgrounds can be explained in this model if the Bino NLSP decays outside the detector. Long life time of the Bino is possible because of high Peccei–Quinn symmetry breaking scale fa. The ALEPH and CDF II data put a very strong bound on fa for light Bino case with mB˜≲150 GeV: the narrow hadronic axion window around fa∼106 GeV is completely closed. The recent ATLAS and CMS data show very interesting bound on fa≳105 GeV for the Bino mass below 700 GeV. This is already stronger than the previous laboratory bounds.

Cosmological aspects of inflation in a supersymmetric axion model

We show that the hybrid inflation is naturally realized in the framework of a supersymmetric axion model, which is consistent with the WMAP observation if the Peccei-Quinn symmetry-breaking scale is around ${10}^{15}\text{ }\text{ }\mathrm{GeV}$. By solving the post-inflationary scalar dynamics, it is found that the scalar partner of the axion, saxion, oscillates with large amplitude and its decay produces a huge entropy and dilutes the axion. As a result, the axion coherent oscillation can be the dominant component of the dark matter in the Universe. Cosmological gravitino and axino problems are solved.

Axion cold dark matter revisited

We study for what specific values of the theoretical parameters the axion can form the totality of cold dark matter. We examine the allowed axion parameter region in the light of recent data collected by the WMAP5 mission plus baryon acoustic oscillations and supernovae [1], and assume an inflationary scenario and standard cosmology. We also upgrade the treatment of anharmonicities in the axion potential, which we find important in certain cases. If the Peccei-Quinn symmetry is restored after inflation, we recover the usual relation between axion mass and density, so that an axion mass ma = (85 ± 3) μeV makes the axion 100% of the cold dark matter. If the Peccei-Quinn symmetry is broken during inflation, the axion can instead be 100% of the cold dark matter for ma < 15 meV provided a specific value of the initial misalignment angle θi is chosen in correspondence to a given value of its mass ma. Large values of the Peccei-Quinn symmetry breaking scale correspond to small, perhaps uncomfortably small, values of the initial misalignment angle θi.

Dark matter axions revisited

We study for what specific values of the theoretical parameters the axion can form the totality of cold dark matter. We examine the allowed axion parameter region in the light of recent data collected by the WMAP5 mission plus baryon acoustic oscillations and supernovae, and assume an inflationary scenario and standard cosmology. If the Peccei-Quinn symmetry is restored after inflation, we recover the usual relation between axion mass and density, so that an axion mass $m_a =67\pm2{\rm \mu eV}$ makes the axion 100% of the cold dark matter. If the Peccei-Quinn symmetry is broken during inflation, the axion can instead be 100% of the cold dark matter for $m_a < 15{\rm meV}$ provided a specific value of the initial misalignment angle $\theta_i$ is chosen in correspondence to a given value of its mass $m_a$. Large values of the Peccei-Quinn symmetry breaking scale correspond to small, perhaps uncomfortably small, values of the initial misalignment angle $\theta_i$.

Cosmological consequences of Yukawa-unified SUSY with mixed axion/axino cold and warm dark matter

Supersymmetric models with t−b−τ Yukawa unification at MGUTqualitatively predict a sparticle mass spectrum including first and second generation scalarsat the 3–15 TeV scale, third generation scalars at the (few) TeV scale and gluinos in the sub-TeV range. The neutralino relic density in these models typically turns out to lie far abovethe measured dark matter abundance, prompting the suggestion that instead dark matter is composed of an axion/axino mixture.We explore the axion and thermal and non-thermal axino dark matter abundance in Yukawa-unified SUSY models. We find in this scenario that (i) rather large values of Peccei-Quinn symmetry breaking scale fa ∼ 1012 GeV are favored and (ii) rather large values of GUT scale scalar masses ∼ 10−15 TeV allow for the re-heat temperature TR of the universe to be TR ⪆ 106 GeV. This allows in turn a solution to the gravitino/Big Bang Nucleosynthesis problem while also allowing for baryogenesis via non-thermal leptogenesis. The large scalar masses for Yukawa-unified models are also favored by data on b → sγ and Bs → μ+μ− decay.Testable consequences from this scenario include a possible axion detection at axion search experiments, but null results from direct and indirect WIMP search experiments.

Axionic mirage mediation

Although mirage mediation is one of the most plausible mediation mechanisms of supersymmetry breaking, it suffers from two crucial problems. One is the $\ensuremath{\mu}/B\ensuremath{\mu}$ problem, and the second is the cosmological one. The former stems from the fact that the $B$ parameter tends to be comparable with the gravitino mass, which is 2 orders of magnitude larger than the other soft masses. The latter problem is caused by the decay of the modulus whose branching ratio into the gravitino pair is sizable. In this paper, we propose a model of mirage mediation, in which Peccei-Quinn symmetry is incorporated. In this axionic mirage mediation, it is shown that the Peccei-Quinn symmetry breaking scale is dynamically determined around ${10}^{10}\text{ }\text{ }\mathrm{GeV}$ to ${10}^{12}\text{ }\text{ }\mathrm{GeV}$ due to the supersymmetry breaking effects, and the $\ensuremath{\mu}$ problem can be solved naturally. Furthermore, in our model, the lightest supersymmetric particle (LSP) is the axino, that is, the superpartner of the axion. The overabundance of the LSPs due to decays of the modulus/gravitino, which is the most serious cosmological difficulty in the mirage mediation, can be avoided if the axino is sufficiently light. The next-LSPs (NLSPs) produced by the gravitino decay eventually decay into the axino LSPs, yielding the dominant component of the axinos remaining today. It is shown that the axino with a mass of $\mathcal{O}(100)\text{ }\text{ }\mathrm{MeV}$ is naturally realized, which can constitute the dark matter of the Universe, with a free-streaming length of the order of $0.1\text{ }\text{ }\mathrm{Mpc}$. The saxion, the real scalar component of the axion supermultiplet, can also be cosmologically harmless due to the dilution of the modulus decay. The lifetime of the NLSP is relatively long, but much shorter than 1 sec, when the big-bang nucleosynthesis commences. The decay of the NLSP would provide intriguing collider signatures.

Preheating curvaton perturbations

We discuss the potentially important role played by preheating in certain variants of the curvaton mechanism in which isocurvature perturbations of a D-flat (and F-flat) direction become converted to curvature perturbations during reheating. We discover that parametric resonance of the isocurvature components amplifies the superhorizon fluctuations by a significant amount. As an example of these effects we develop a particle physics motivated model which involves hybrid inflation with the waterfall field N being responsible for generating the ? term, the right-handed neutrino mass scale, and the Peccei-Quinn symmetry breaking scale. The role of the curvaton field can be played either by usual Higgs field, or the lightest right-handed sneutrino. Our new results show that it is possible to achieve the correct curvature perturbations for initial values of the curvaton fields of order the weak scale. In this model we show that the prediction for the spectral index of the final curvature perturbation only depends on the mass of the curvaton during inflation, where consistency with current observational data requires the ratio of this mass to the Hubble constant to be less-than-or-equals, slant 0.3.

Model of cosmology and particle physics at an intermediate scale

We propose a model of cosmology and particle physics in which all relevant scales arise in a natural way from an intermediate string scale. We are led to assign the string scale to the intermediate scale ${M}_{*}\ensuremath{\sim}{10}^{13}\text{ }\text{ }\mathrm{GeV}$ by four independent pieces of physics: electroweak symmetry breaking; the $\ensuremath{\mu}$ parameter; the axion scale; and the neutrino mass scale. The model involves hybrid inflation with the waterfall field $N$ being responsible for generating the $\ensuremath{\mu}$ term, the right-handed neutrino mass scale, and the Peccei-Quinn symmetry breaking scale. The large scale structure of the Universe is generated by the lightest right-handed sneutrino playing the r\^ole of a coupled curvaton. We show that the correct curvature perturbations may be successfully generated providing the lightest right-handed neutrino is weakly coupled in the seesaw mechanism, consistent with sequential dominance.