PQ Breaking Research Articles

Dynamics of superconformal axion: Quality and scalegenesis

We explore a dynamical mechanism to realize the emergence of a global U(1)PQ symmetry and its spontaneous breaking at an intermediate scale for an axion solution to the strong CP problem. Such a dynamics is provided by a new supersymmetric QCD near the middle of conformal window that couples to fields spontaneously breaking the U(1)PQ symmetry. A large anomalous dimension of the U(1)PQ breaking fields leads to the suppression of explicit U(1)PQ-violating higher dimensional operators. The U(1)PQ breaking vacuum is generated at a scale hierarchically smaller than the Planck scale by a non-perturbative effect. The U(1)PQ breaking drives the conformal breaking, and all the new quarks become massive. The axion potential is generated by the ordinary color SU(3)C effect as the U(1)PQ symmetry is only anomalous under the SU(3)C. The saxion direction is stabilized by supersymmetry breaking and cosmologically harmless.

Axion dark matter with thermal friction

Cosmological evolution of axion field in the early universe might be significantly affected by a thermal friction induced by the axion coupling to thermalized hidden sector. We examine the effects of such a thermal friction on axion dark matter density and its perturbation when the thermal friction dominates over the Hubble friction until when the axion field begins to oscillate around the potential minimum. We show that in the presence of sizable thermal friction there can be an exponential decay phase of the axion field before the oscillation phase, during which the axion energy density is efficiently dissipated into hidden thermal bath. Consequently, the previously excluded parameter region due to overclosing relic axion density becomes cosmologically viable with thermal friction. In particular, a QCD axion much lighter than μeV is viable without tuning the initial misalignment angle. We also find that thermal friction can affect the density perturbation of axion dark matter in various ways. For instance, it can alleviate the large-scale isocurvature bound on axion dark matter in the pre-inflationary PQ breaking scenario, which would make the pre-inflationary axion dark matter compatible with high scale inflation over a wide range of model parameters. In the post-inflationary PQ breaking scenario, thermal friction can also significantly change the scaling behavior of axionic strings, and therefore the typical size of the resultant axion miniclusters.

Flavoured warped axion

We consider a 5D extension of the DFSZ axion model that addresses both the axion quality and fermion mass hierarchy problems, and predicts flavour-dependent, off-diagonal axion-fermion couplings. The axion is part of a 5D complex scalar field charged under a U(1)PQ symmetry that is spontaneously broken in the bulk, and is insensitive to explicit PQ breaking on the UV boundary. Bulk Standard Model fermions interact with two Higgs doublets that can be localized on the UV boundary or propagate in the bulk to explain the fermion masses and mixings. When the Higgs doublets are localized on the UV boundary, they induce flavour diagonal couplings between the fermions and the axion. However, when the Higgs doublets propagate in the bulk, the overlap of the axion and fermion profiles generates flavour off-diagonal couplings. The effective scale of these off-diagonal couplings in both the quark and lepton sectors can be as small as 1011 GeV, and therefore will be probed in future precision flavour experiments.

Axion quality from superconformal dynamics

We discuss a possibility that a superconformal dynamics induces the emergence of a global U(1)PQ symmetry to solve the strong CP problem through the axion. Fields spontaneously breaking the U(1)PQ symmetry couple to new quarks charged under the ordinary color SU(3)C and a new SU(N) gauge group. The theory flows into an IR fixed point where the U(1)PQ breaking fields hold a large anomalous dimension leading to the suppression of U(1)PQ-violating higher dimensional operators. The spontaneous breaking of the U(1)PQ makes the new quarks massive. The U(1)PQ symmetry is anomalous under the SU(3)C but not under the SU(N) so that the axion couples to only the color SU(3)C and the usual axion potential is generated. We also comment on a model that the U(1)PQ breaking fields are realized as meson superfields in a new supersymmetric QCD.

Axion model with intermediate scale fermionic dark matter

We investigate a non-supersymmetric SO(10)×U(1)PQ axion model in which the spontaneous breaking of U(1)PQ occurs after inflation, and the axion domain wall problem is resolved by employing the Lazarides-Shafi mechanism. This requires the introduction of two fermion 10-plets, such that the surviving discrete symmetry from the explicit U(1)PQ breaking by QCD instantons is reduced from Z12 to Z4, where Z4 coincides with the center of SO(10) (more precisely Spin(10)). An unbroken Z2 subgroup of Z4 yields intermediate scale topologically stable strings, as well as a stable electroweak doublet non-thermal dark matter candidate from the fermion 10-plets with mass comparable to or somewhat smaller than the axion decay constant fa. We present an explicit realization with inflation taken into account and which also incorporates non-thermal leptogenesis. The fermion dark matter mass lies in the 3×108−1010GeV range and its contribution to the relic dark matter abundance can be comparable to that from the axion.

Affleck-Dine leptogenesis with varying Peccei-Quinn scale

The Affleck-Dine leptogenesis scenario along the LHu flat direction is reconsidered. It is known that successful Affleck-Dine leptogenesis requires that the lightest neutrino mass is extremely small. This situation can be significantly relaxed if the neutrino mass in the early universe is different from the present one. We consider a supersymmetric Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) type model, which provides a solution to the strong CP problem and generates a SUSY μ-term and right-handed neutrino masses. If the PQ scale during lepton number generation is much larger than the present value, leptogenesis is very efficient so that enough baryon number can be generated without introducing a hierarchically small neutrino mass. The final baryon asymmetry is related to the μ-term, and hence linked to the level of electroweak fine-tuning. We also show the PQ breaking scalar dynamics that keeps a large PQ breaking scale during inflation and lepton number generation. The μ-term generating superpotential plays an important role for preserving the lepton asymmetry during saxion oscillation. In this scenario, the axion isocurvature perturbation is naturally suppressed.

Cosmologically safe QCD axion as a present from extra dimension

We propose a QCD axion model where the origin of PQ symmetry and suppression of axion isocurvature perturbations are explained by introducing an extra dimension. Each extra quark–antiquark pair lives on branes separately to suppress PQ breaking operators. The size of the extra dimension changes after inflation due to an interaction between inflaton and a bulk scalar field, which implies that the PQ symmetry can be drastically broken during inflation to suppress undesirable axion isocurvature fluctuations.

Mixed axion-wino dark matter

A variety of supersymmetric models give rise to a split mass spectrum characterized by very heavy scalars but sub-TeV gauginos, usually with a wino-like LSP. Such models predict a thermally-produced underabundance of wino-like WIMP dark matter so that non-thermal DM production mechanisms are necessary. We examine the case where theories with a wino-like LSP are augmented by a Peccei-Quinn sector including an axion-axino-saxion supermultiplet in either the SUSY KSVZ or SUSY DFSZ models and with/without saxion decays to axions/axinos. We show allowed ranges of PQ breaking scale f_a for various cases which are generated by solving the necessary coupled Boltzmann equations. We also present results for a model with radiatively-driven naturalness but with a wino-like LSP.

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.

Multiverse dark matter: SUSY or axions

The observed values of the cosmological constant and the abundance of Dark Matter (DM) can be successfully understood, using certain measures, by imposing the anthropic requirement that density perturbations go non-linear and virialize to form halos. This requires a probability distribution favoring low amounts of DM, i.e. low values of the PQ scale f for the QCD axion and low values of the superpartner mass scale $$ \tilde{m} $$ for LSP thermal relics. In theories with independent scanning of multiple DM components, there is a high probability for DM to be dominated by a single component. For example, with independent scanning of f and $$ \tilde{m} $$ , TeV-scale LSP DM and an axion solution to the strong CP problem are unlikely to coexist. With thermal LSP DM, the scheme allows an understanding of a Little SUSY Hierarchy with multi-TeV superpartners. Alternatively, with axion DM, PQ breaking before (after) inflation leads to f typically below (below) the projected range of the current ADMX experiment of f = (3 − 30) × 1011 GeV, providing strong motivation to develop experimental techniques for probing lower f.

Coupled Boltzmann computation of mixed axion neutralino dark matter in the SUSY DFSZ axion model

The supersymmetrized DFSZ axion model is highly motivated not only because it offers solutions to both the gauge hierarchy and strong CP problems, but also because it provides a solution to the SUSY μ-problem which naturally allows for a Little Hierarchy. We compute the expected mixed axion-neutralino dark matter abundance for the SUSY DFSZ axion model in two benchmark cases—a natural SUSY model with a standard neutralino underabundance (SUA) and an mSUGRA/CMSSM model with a standard overabundance (SOA). Our computation implements coupled Boltzmann equations which track the radiation density along with neutralino, axion, axion CO (produced via coherent oscillations), saxion, saxion CO, axino and gravitino densities. In the SUSY DFSZ model, axions, axinos and saxions go through the process of freeze-in—in contrast to freeze-out or out-of-equilibrium production as in the SUSY KSVZ model—resulting in thermal yields which are largely independent of the re-heat temperature. We find the SUA case with suppressed saxion-axion couplings (ξ=0) only admits solutions for PQ breaking scale fa≲ 6× 1012 GeV where the bulk of parameter space tends to be axion-dominated. For SUA with allowed saxion-axion couplings (ξ =1), then fa values up to ∼ 1014 GeV are allowed. For the SOA case, almost all of SUSY DFSZ parameter space is disallowed by a combination of overproduction of dark matter, overproduction of dark radiation or violation of BBN constraints. An exception occurs at very large fa∼ 1015–1016 GeV where large entropy dilution from CO-produced saxions leads to allowed models.

Revisit to non-decoupling MSSM

Dipole operator s¯σμνFμνb requires the helicity flip in the involving quark states thus the breaking of chiral U(3)Q×U(3)d. On the other hand, the b quark mass generation is also a consequence of chiral U(3)Q×U(3)d symmetry breaking. Therefore, in many models, there might be strong correlation between the b→sγ and b quark Yukawa coupling. In this Letter, we use non-decoupling MSSM model to illustrate this feature. In the scenario, the light Higgs boson may evade the direct search experiments at LEPII or Tevatron while the 125 GeV Higgs-like boson is identified as the heavy Higgs boson in the spectrum. A light charged Higgs is close to the heavy Higgs boson which is of 125 GeV and its contribution to b→sγ requires large supersymmetric correction with large PQ and R-symmetry breaking. The large supersymmetric contribution at the same time significantly modifies the b quark Yukawa coupling. With combined flavor constraints B→Xsγ and Bs→μ+μ− and direct constraints on Higgs properties, we find best fit scenarios with light stop of O(500 GeV), negative At around −750 GeV and large μ-term of 2–3 TeV. In addition, reduction in bb¯ partial width may also result in large enhancement of ττ decay branching fraction. Large parameter region in the survival space under all bounds may be further constrained by H→ττ if no excess of ττ is confirmed at LHC. We only identify a small parameter region with significant H→hh decay that is consistent with all bounds and reduced ττ decay branching fraction. In the end, if current dark matter mostly consists of neutralino, direct detection experiments like XENON100 also puts stringent bound over this scenario with light Higgs bosons. The light stops which are required by flavor constraints can further enhance the scattering cross section.

2 Higgs or not 2 Higgs

Motivated by recent results from the LHC experiments, we analyze Higgs couplings in two Higgs doublet models with an approximate PQ symmetry. Models of this kind can naturally accommodate sizable modifications to Higgs decay patterns while leaving production at hadron colliders untouched. Near the decoupling limit, we integrate out the heavy doublet to obtain the effective couplings of the SM-like Higgs and express these couplings in a physically transparent way, keeping all orders in (mh/mH) for small PQ breaking. Considering supersymmetric models, we show that the effects on the Higgs couplings are considerably constrained.

Thermal leptogenesis and the gravitino problem in the Asaka-Yanagida axion/axino dark matter scenario

A successful implementation of thermal leptogenesis requires the re-heat temperature after inflation TR to exceed ∼ 2 × 109 GeV. Such a high TR value typically leads to an overproduction of gravitinos in the early universe, which will cause conflicts, mainly with BBN constraints. Asaka and Yanagida (AY) have proposed that these two issues can be reconciled in the context of the Peccei-Quinn augmented MSSM (PQMSSM) if one adopts a mass hierarchy m(sparticle) > m(gravitino)>m(axino), with m(axino) ∼ keV. In this case, sparticle decays bypass the gravitino, and decay more quickly to the axino LSP, thus avoiding the BBN constraints. In addition, thermally produced gravitinos decay inertly to axion+axino, also avoiding BBN constraints. We calculate the relic abundance of mixed axion/axino dark matter in the AY scenario, and investigate under what conditions a value of TR sufficient for thermal leptogenesis can be generated. A high value of PQ breaking scale fa is needed to suppress overproduction of axinos, while a small vacuum misalignment angle θi is needed to suppress overproduction of axions. The large value of fa results in late decaying neutralinos. We show that, to avoid BBN constraints, the AY scenario requires a rather low thermal abundance of neutralinos, while higher values of neutralino mass also help. We combine these constraint calculations along with entropy production from late decaying saxions, and find the saxion needs to be typically at least several times heavier than the gravitino. A successful implementation of the AY scenario suggests that LHC should discover a spectrum of SUSY particles consistent with weak scale supergravity; that the apparent neutralino abundance is low; that an axion direct detection signal (probably with ma in the sub-μeV range) may be possible, but no direct or indirect signals for WIMP dark matter should be observed.

Axion protection from flavor

The QCD axion fails to solve the strong CP problem unless all explicit PQ violating, Planck-suppressed, dimension n < 10 operators are forbidden or have exponentially small coefficients. We show that all theories with a QCD axion contain an irreducible source of explicit PQ violation which is proportional to the determinant of the Yukawa interaction matrix of colored fermions. Generically, this contribution is of low operator dimension and will drastically destabilize the axion potential, so its suppression is a necessary condition for solving the strong CP problem. We propose a mechanism whereby the PQ symmetry is kept exact up to n = 12 with the help of the very same flavor symmetries which generate the hierarchical quark masses and mixings of the SM. This “axion flavor protection” is straightforwardly realized in theories which employ radiative fermion mass generation and grand unification. A universal feature of this construction is that the heavy quark Yukawa couplings are generated at the PQ breaking scale.

Formula omitted] SUSY GUTs, the gravitino problem, non-thermal leptogenesis and axino dark matter

Simple SUSY GUT models based on the gauge group SO(10) require t–b–τ Yukawa coupling unification, in addition to gauge coupling and matter unification. The Yukawa coupling unification places strong constraints on the expected superparticle mass spectrum, with scalar masses ∼10 TeV while gaugino masses are quite light. A problem generic to all supergravity models comes from overproduction of gravitinos in the early universe: if gravitinos are unstable, then their late decays may destroy the predictions of Big Bang nucleosynthesis. We present a Yukawa-unified SO(10) SUSY GUT scenario which avoids the gravitino problem, gives rise to the correct matter–antimatter asymmetry via non-thermal leptogenesis, and is consistent with the WMAP-measured abundance of cold dark matter due to the presence of an axino LSP. To maintain a consistent cosmology for Yukawa-unified SUSY models, we require a re-heat temperature TR∼106–107 GeV, an axino mass around ∼0.1–10 MeV, and a PQ breaking scale fa∼1012 GeV.

Spontaneous CP violation in SUSY [formula omitted

A scenario is suggested for spontaneous CP violation in non-SUSY and SUSY SO ( 10 ) . The idea is to have a scalar potential which generates spontaneously a phase, at the high scale, in the VEV that gives a mass to the RH neutrinos. As a possible realization the case of the minimal renormalizable SUSY SO ( 10 ) is discussed in detail and one finds that a phase is induced in the CKM matrix. It is also pointed out that, in these models, the scales of Baryogenesis, Seesaw, Spontaneous CP violation and Spontaneous U ( 1 ) PQ breaking are all of the same order of magnitude.

On axion and familons

We study the connection between the global family symmetry G F=SU( N) and Peccei-Quinn symmetry U(1) PQ in the context of SO(10). It turns out that GF automatically leads to U(1) PQ, if the Higgs representation is properly restricted. This implies that the decay K + → π + + nothing (Goldstone boson) should be observable soon. Furthermore, for odd number of families, the theory is free from the axionic domain wall problem. Finally, if B— L breaking is tied to G F and U(1) PQ breaking, the theory favors three families of fermions.