Light weakly coupled axial forces: models, constraints, and projections

Kahn, Yonatan; Krnjaic, Gordan; Mishra-Sharma, Siddharth; Tait, Tim M. P.

doi:10.1007/jhep05(2017)002

Cited by 89 publications

(116 citation statements)

References 78 publications

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“…Moreover, a theory with axial-vector couplings motivated by several MeV-scale anomalies can be UV-completed consistent with the Standard Model gauge invariance, see Refs. [36,37] for details. In Ref.…”

Section: (Right) Where Two Cms Energies (mentioning

confidence: 99%

“…[30], the production of a hidden vector boson with axial-vector couplings to leptons and light quarks in the isoscalar 8 Be * → 8 Be nuclear transition is investigated. Note, along with the axialvector couplings to the Standard Model fermions, we need to devote some effort to obtain a UV-complete anomaly-free theory [36,37]. Besides, models including this X boson as a mediator to the dark sector or giving constrains on dark matters are discussed [38][39][40][41].…”

Section: Introductionmentioning

confidence: 99%

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X(16.7) production in electron–positron collision

et al. 2018

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The anomaly found in the excited 8 Be nuclear transition to its ground state is attributed to a spin-1 gauge boson X (16.7). To hunt for this boson, we propose two traps: e + e − → X γ and J/ψ → X γ , both following with X → e + e − decay. We adopt the "vector minus axial-vector" interaction hypothesis. Analysis on the X (16.7) decay length, production rates, differential distribution with respect to the e + e − invariant-mass spectrum, and the signal-to-noise ratios (SNR) after the smearing at BESIII detector are discussed in detail. Given the coupling strength of X to vector/axial-vector currents g v/a f ∼ 10 −3 at BESIII: (1) there would be about 6000 X measurable events per year in electron-positron collision, yet with a large background after smearing; (2) while in J/ψ decays, we find that the axial-vector current may come into play; though merely 52 events may appear, the SNR are inspiring even after smearing.

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Section: (Right) Where Two Cms Energies (mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

X(16.7) production in electron–positron collision

et al. 2018

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“…(10a) and (10b), these bounds can be translated into constraints for ε p and ε n . These constraints are so stringent that they are incompatible with the experimental 4 In [18] the NA48/2 constraint on U (1) d model is also applied similarly. 5 An example of constraining U (1) B−L model by using ν − e scattering experiment can be found in [22].…”

Section: B ν − E Scattering Experimental Constraintmentioning

confidence: 99%

The 17 MeV Anomaly in Beryllium Decays and U(1) Portal to Dark Matter

Chen

Lin²,

Lin³

et al. 2017

Proceedings of the European Physical Society Conference on High Energy Physics — PoS(EPS-HEP2017)

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The experiment of Krasznahorkay et al observed the transition of a 8 Be excited state to its ground state and accompanied by an emission of e + e − pair with 17 MeV invariant mass. This 6.8σ anomaly can be fitted by a new light gauge boson. We consider the new particle as a U (1) gauge boson, Z , which plays as a portal linking dark sector and visible sector. In particular, we study the new U (1) gauge symmetry as a hidden or non-hidden group separately. The generic hidden U (1) model, referred to as dark Z model, is excluded by imposing various experimental constraints. On the other hand, a non-hidden Z is allowed due to additional interactions between Z and Standard Model fermions. We also study the implication of the dark matter direct search on such a scenario. We found the search for the DM-nucleon scattering cannot probe the parameter space that is allowed by 8 Be-anomaly for the range of DM mass above 500 MeV. However, the DM-electron scattering for DM between 20 and 50 MeV can test the underlying U (1) portal model using the future Si and Ge detectors with 5e − threshold charges.

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“…In particular, when only a SU (2) doublet is taken into account, the C f,A coefficients are suppressed with respect to the vector-like counterparts (see [16]). This is a direct consequence of the gauge invariance of the Yukawa interactions which forces the U (1) ′ charge of the Higgs field to satisfy the conditions…”

mentioning

confidence: 99%

“…The anomaly cancellation condition arising from the U (1) ′ SU (3)SU (3) diagram and the gauge invariance of the Yukawa Lagrangian require 2z Q − z d − z u = z Φ1 − z Φ2 = 0, which necessarily calls for extra coloured states when z Φ1 = z Φ2 . These new states must be vector-like under the SM gauge group and chiral under the extra U (1) ′ [16].…”

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confidence: 99%

Explanation of the 17 MeV Atomki anomaly in a U(1)′ -extended two Higgs doublet model

2017

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Motivated by an anomaly observed in the decay of an excited state of Beryllium ( 8 Be) by the Atomki collaboration, we study an extension of the Standard Model with a gauged U (1) ′ symmetry in presence of a 2-Higgs Doublet Model structure of the Higgs sector. We show that this scenario complies with a variety of experimental results and is able to explain the potential presence of a resonant spin-1 gauge boson, Z ′ , with a mass of 17 MeV in the Atomki experimental data, for appropriate choices of U (1) ′ charges and Yukawa interactions.The Atomki pair spectrometer experiment [1] was set up for searching e + e − internal pair creation in the decay of excited 8 Be nuclei (henceforth, 8 Be * ), the latter being produced with the help of a beam of protons directed on a Lithium ( 7 Li) target. The proton beam was tuned in such a way that the different 8 Be excitations could be separated with high accuracy.In the data collection stage, a clear anomaly was observed in the decay of 8 Be * with spin-parity J P = 1 + into the ground state 8 Be with spin-parity 0 + (both with isospin T = 0), where 8 Be * had an excitation energy of 18.15 MeV. Upon analysis of the electron-positron properties, the spectra of both their opening angle θ and invariant mass M presented the characteristics of an excess consistent with an intermediate boson X being produced on-shell in the decay of the 8 Be * state, with the X object subsequently decaying into e + e − pairs. The best fit to the mass M X of X was given as [1] M X = 16.7 ± 0.35 (stat) ± 0.5 (sys) MeV, in correspondence of a ratio of Branching Ratios (BRs) obtained asThis combination yields a statistical significance of the excess of about 6.8 σ [1].An explanation of the X nature was attempted by [2,3], in the form of models featuring a new vector boson Z ′ with a mass M Z ′ of about 17 MeV, with vector-like couplings to quarks and leptons. Constraints on such a new state, notably from searches for π 0 → Z ′ + γ by the NA48/2 experiment [4], require the couplings of the Z ′ to up and down quarks to be 'protophobic', i.e., that the charges eǫ u and eǫ d of up and down quarks -written as multiples of the positron charge e -satisfy the relation 2ǫ u + ǫ d < ∼ 10 −3 [2,3]. Subsequently, further studies of such models have been performed in [5-12] 1 .1 An alternative explanation was given in [13], wherein the X was In the footsteps of this literature, we consider here an extension of the SM described by a generic U (1) ′ group. Due to the presence of two such Abelian symmetries, U (1) Y × U (1) ′ , the most general kinetic Lagrangian of the corresponding fields,B µ andB ′ µ , respectively, allows for a gauge invariant mixing of the two field-strengthswhere κ is the kinetic mixing parameter between U (1) Y and U (1) ′ . A diagonal form for this Lagrangian can be obtained by transformation of the Abelian fields such that the gauge covariant derivative becomeswhere Y and z are the hypercharge and U (1) ′ charge, respectively, andg the gauge coupling mixing between the two Abelian groups. ...

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Light weakly coupled axial forces: models, constraints, and projections

Cited by 89 publications

References 78 publications

X(16.7) production in electron–positron collision

X(16.7) production in electron–positron collision

The 17 MeV Anomaly in Beryllium Decays and U(1) Portal to Dark Matter

Explanation of the 17 MeV Atomki anomaly in a U(1)′ -extended two Higgs doublet model

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