In some models of physics beyond the Standard Model (SM), one of the leading low energy consequences of the model appears in the form of the chromo-electric dipole moments (CEDMs) of the gluons and light quarks. We examine if these CEDMs can be distinguished from the QCD θ-term through the experimentally measurable nuclear and atomic electric dipole moments (EDMs) in both cases with and without the Peccei-Quinn (PQ) mechanism solving the strong CP problem. We find that the nucleon EDMs show a distinctive pattern when the EDMs are dominantly induced by the light quark CEDMs without the PQ mechanism. In the presence of the PQ mechanism, the QCD θ-parameter corresponds to the vacuum value of the axion field, which might be induced either by CEDMs or by UV-originated PQ breaking other than the QCD anomaly, for instance the PQ breaking by quantum gravity effects. We find that in case with the PQ mechanism the nucleon EDMs have a similar pattern regardless of what is the dominant source of EDMs among the CEDMs and θ-term, unless there is a significant cancellation between the contributions from different sources. In contrast, some nuclei or atomic EDMs can have characteristic patterns significantly depending on the dominant source of EDMs, which may allow identifying the dominant source among the CEDMs and θ-term. Yet, discriminating the gluon CEDM from the QCD θ-parameter necessitates additional knowledge of low energy parameters induced by the gluon CEDM, which is not available at the moment. Our results imply that EDMs can reveal unambiguous sign of CEDMs while identifying the origin of the axion vacuum value, however it requires further knowledge of low energy parameters induced by the gluon CEDM.

South Korea

Kiwoon Choi

Sang Im

Krzysztof Jodłowski

Exploring CP violation beyond the Standard Model and the PQ quality with electric dipole moments

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.

Hee Kim

Germany

Hyeonseok Seong

Axion dark matter with thermal friction

We examine the axion emission from supernovae with a complete set of relevant axion couplings including the axion-pion-nucleon contact interaction which was ignored in the previous studies. Two processes are affected by the axion-pion-nucleon contact interaction, π  −  + p → n + a and n + p → n + p + a, and these processes can be the dominant source of axions for some region in the axion parameter space or in astrophysical conditions encountered inside supernovae. We find that the contact interaction can enhance the axion emissivity of π  −  + p → n + a by a factor of 2 − 4, while the effect on n + p → n + p + a is not significant. We also discuss the relative importance of other pion-induced processes such as π 0 + n → n + a and π  −  + π 0 → π  −  + a.

Chang Shin

Axion emission from supernova with axion-pion-nucleon contact interaction

We study the renormalization group running of axion couplings while taking into account that the Standard Model can be extended to its supersymmetric extension at a certain energy scale below the axion decay constant. We then apply our results to three different classes of axion models, i.e. KSVZ-like, DFSZ-like, and string-theoretic axions, and examine if string-theoretic axions can be distinguished from others by having a different pattern of low energy couplings to the photon, nucleons and electron. We find that the low energy couplings of string-theoretic axions have a similar pattern as those of KSVZ-like axions but yet reveal a sizable difference which might be testable in future axion search experiments. We also note that the coupling of KSVZ-like QCD axions to the electron is dominated by a three-loop contribution involving the exotic heavy quark, gluons, top quark and Higgs field.

Precision axion physics with running axion couplings

We examine the resonant conversion of axionlike particle (ALP) or dark photon to the electromagnetic photon in the early Universe, which takes place due to the ALP-photon-dark photon oscillations in background dark photon gauge fields. It is noted that the corresponding conversion probability can have an unusual spectral feature which allows strong conversion at low frequency domain, but has negligible conversion at high frequencies above certain critical frequency which is determined by the ALP coupling to dark photon and the strength of background dark photon gauge field. We apply this scheme to heat up the 21-cm photons without affecting the cosmic microwave background, which can explain the tentative absorption signal of 21-cm photons detected recently by the EDGES experiment.

Seokhoon Yun

Axion-photon-dark photon oscillation and its implication for 21-cm observation

Recently it has been noticed that the Fermi-LAT data of gamma-rays from some galactic pulsars and supernova remnants reveal spectral modulations that might be explained by the conversion of photons to ALPs (axionlike particles) induced by the conventional ALP coupling to photon in the presence of galactic magnetic fields. However the corresponding ALP mass and coupling are in a severe tension with the observational constraints from CAST, SN1987A, and other gamma-ray observations. Motivated by this, we examine an alternative possibility that those spectral modulations are explained by other type of ALP coupling involving both the ordinary photon and a massless dark photon, when nonzero background dark photon gauge fields are assumed. We find that our scheme results in oscillations among the photon, ALP, and dark photon, which can explain the gamma-ray spectral modulations of galactic pulsars or supernova remnants, while satisfying the known observational constraints.

Sangjun Lee

Gamma-ray spectral modulations induced by photon-ALP-dark photon oscillations

Physics beyond the Standard Model (SM) may manifest itself as small deviations from the SM predictions for Higgs signal strengths at 125 GeV. Then, a plausible and interesting possibility is that the Higgs sector is extended and at the weak scale there appears an additional Higgs boson weakly coupled to the SM sector. Combined with the LEP excess in $$e^+e^-\rightarrow Z(h\rightarrow b\bar{b})$$ <math><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>-</mo></msup><mo>→</mo><mi>Z</mi><mrow><mo>(</mo><mi>h</mi><mo>→</mo><mi>b</mi><mover><mrow><mi>b</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>)</mo></mrow></mrow></math> , the diphoton excess around 96 GeV recently reported by CMS may suggest such a possibility. We examine if those LEP and CMS excesses can be explained simultaneously by a singlet-like Higgs boson in the general next-to-minimal supersymmetric Standard Model (NMSSM). Higgs mixing in the NMSSM relies on the singlet coupling to the MSSM Higgs doublets and the higgsino mass parameter, and thus is subject to the constraints on these supersymmetric parameters. We find that the NMSSM can account for both the LEP and CMS excesses at 96 GeV while accommodating the observed 125 GeV SM-like Higgs boson. Interestingly, the required mixing angles constrain the heavy doublet Higgs boson to be heavier than about 500 GeV. We also show that the viable region of mixing parameter space is considerably modified if the higgsino mass parameter is around the weak scale, mainly because of the Higgs coupling to photons induced by the charged higgsinos.

Kwang Jeong

Chan Park

Light Higgs bosons in the general NMSSM

The dS swampland conjecture |∇V|/V ≥ c, where c is presumed to be a positive constant of order unity, implies that the dark energy density of our Universe can not be a cosmological constant, but mostly the potential energy of an evolving quintessence scalar field. As the dark energy includes the effects of the electroweak symmetry breaking and the QCD chiral symmetry breaking, if the dS swampland conjecture is applicable for the low energy quintessence potential, it can be applied for the Higgs and pion potential also. On the other hand, the Higgs and pion potential has the well-known dS extrema, and applying the dS swampland conjecture to those dS extrema may provide stringent constraints on the viable quintessence, as well as on the conjecture itself. We examine this issue and find that the pion dS extremum at cos(π 0/f  π ) = −1 implies c ≲   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (10−2–10−5) for arbitrary form of the quintessence potential and couplings, where the weaker bound (10−2) is available only for a specific type of quintessence whose couplings respect the equivalence principle, while the stronger bound (10−5) applies for generic quintessence violating the equivalence principle. We also discuss the possibility to relax this bound with an additional scalar field, e.g. a light modulus which has a runaway behavior at the pion dS extremum. We argue that such possibility is severely constrained by a variety of observational constraints which do not leave a room to significantly relax the bound. We make a similar analysis for the Higgs dS extremum at H = 0, which results in a weaker bound on c.

Dongjin Chway

The dS swampland conjecture with the electroweak symmetry and QCD chiral symmetry breaking

The continuum clockwork is an extra-dimensional set-up to realize certain features of the clockwork mechanism generating exponentially suppressed or hierarchical couplings of light particles. We study the continuum clockwork in a general scheme in which large volume, warped geometry, and localization of zero modes in extra dimension are described by independent parameters. For this, we propose a generalized 5-dimensional linear dilaton model which can realize such set-up as a solution of the model, and examine the KK spectrum and the couplings of zero modes and massive KK modes to boundary-localized operators for the bulk graviton, Abelian gauge bosons and periodic scalar fields. We discuss how those KK spectra and couplings vary as a function of the volume, warping and localization parameters, and highlight the behavior in the parameter region corresponding to the clockwork limit. We discuss also the field range of 4-dimensional axions originating from either 5-dimensional periodic scalar field or the 5-th component of an Abelian gauge field, and comment on the limitations of continuum clockwork compared to the discrete clockwork.

General continuum clockwork

We propose a mechanism generating primordial magnetic fields after the <math><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> annihilations. Our mechanism involves an ultralight axionlike particle (ALP) which constitutes the dark matter and a dark <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>X</mi></msub></math> gauge boson introduced to bypass the obstacle placed by the conductivity of cosmic plasma. In our scheme, a coherently oscillating ALP amplifies the dark photon field, and part of the amplified dark photon field is concurrently converted to the ordinary magnetic field through the ALP-induced magnetic mixing. For the relevant ALP mass range <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>21</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi><mo>≲</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow></msub><mo>≲</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>17</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math>, our mechanism can generate <math><mi>B</mi><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>24</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>G</mi><mo>(</mo><msub><mi>m</mi><mi>ϕ</mi></msub><mo>/</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>17</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi><msup><mo>)</mo><mrow><mn>5</mn><mo>/</mo><mn>4</mn></mrow></msup></math> with a coherent length <math><mrow><mi>λ</mi><mo>∼</mo><mo>(</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow></msub><mo>/</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>17</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi><msup><mrow><mo>)</mo></mrow><mrow><mo>−</mo><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup><mtext> </mtext><mi>kpc</mi></mrow></math>, which is large enough to provide a seed of the galactic magnetic fields. The mechanism also predicts a dark <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>X</mi></msub></math> electromagnetic field <math><msub><mi>E</mi><mi>X</mi></msub><mo>∼</mo><msub><mi>B</mi><mi>X</mi></msub><mo>∼</mo><mn>80</mn><mtext> </mtext><mtext> </mtext><mi>nG</mi><mo>(</mo><msub><mi>m</mi><mi>ϕ</mi></msub><mo>/</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>17</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi><msup><mo>)</mo><mrow><mo>−</mo><mn>1</mn><mo>/</mo><mn>4</mn></mrow></msup></math>, which can result in interesting astrophysical or cosmological phenomena by inducing the mixings between the ALP, ordinary photon, and dark photon states.