Baryogenesis from oscillations of charmed or beautiful baryons

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Baryogenesis from oscillations of charmed or beautiful baryons

Kyle Aitken, David McKeen, Thomas Neder, and Ann E. Nelson

Phys. Rev. D 96, 075009 – Published 9 October 2017

Abstract

We propose a model for $C P$ -violating oscillations of neutral, heavy-flavor baryons into antibaryons at rates which are within a few orders of magnitude of their lifetimes. The flavor structure of the baryon violation suppresses neutron oscillations and baryon-number-violating nuclear decays to experimentally allowed rates. We also propose a scenario for producing such baryons in the early Universe via the out-of-equilibrium decays of a neutral particle, after hadronization but before nucleosynthesis. We find parameters where $C P$ -violating baryon oscillations at a temperature of a few MeV could result in the observed asymmetry between baryons and antibaryons. Furthermore, part of the relevant parameter space for baryogenesis is potentially testable at Belle II via decays of heavy-flavor baryons into an exotic neutral fermion. The model introduces four new particles: three light Majorana fermions and a colored scalar. The lightest of these fermions is typically long lived on collider time scales and may be produced in decays of bottom and possibly charmed hadrons.

Received 18 August 2017

DOI:https://doi.org/10.1103/PhysRevD.96.075009

Physics Subject Headings (PhySH)

Baryogenesis & leptogenesis Particle mixing & oscillations

Heavy baryons

Baryon & lepton number symmetries

Particles & FieldsGravitation, Cosmology & Astrophysics

Authors & Affiliations

Kyle Aitken^1,*, David McKeen^2,†, Thomas Neder^3,‡, and Ann E. Nelson^1,§

¹Department of Physics, University of Washington, Seattle, Washington 98195, USA
²Pittsburgh Particle Physics, Astrophysics, and Cosmology Center, Department of Physics and Astronomy, University of Pittsburgh, Pennsylvania 15260, USA
³AHEP Group, Instituto de Física Corpuscular—C.S.I.C./Universitat de València, Parc Científic de Paterna, C/ Catedrático José Beltrán 2 E-46980 Paterna (Valencia), Spain

^*kaitken17@gmail.com
^†dmckeen@pitt.edu
^‡neder@ific.uv.es
^§aenelson@uw.edu

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Vol. 96, Iss. 7 — 1 October 2017

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Images

Figure 1
The basic six-quark $Δ B = 2$ operator generated by $ϕ$ and $χ$ exchange. $u$ and $d$ here represent any of the up- or down-type quark flavors. The quarks involved are all weak SU(2) singlets, as emphasized by the $R$ subscripts.
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Figure 2
Left: Dinucleon decay via the $Δ B = Δ S = 2$ $(u d s)^{2}$ operator that mediates $Λ^{0} \leftrightarrow {\bar{Λ}}^{0}$ oscillations. Right: Dinucleon decay mediated by the $Δ B = 2$ , $Δ S = 4$ $(u s s)^{2}$ operator that becomes the $Δ S = 3$ $(u d s) (u s s)$ operator in the presence of flavor-changing weak interactions. Because the short-distance $Δ B = 2$ operators we consider involve weak isosinglets, this operator requires light quark chirality flips, indicated by crosses. See text for a discussion of the matching of the short distance theory onto the (chiral-symmetry-violating) long distance theory.
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Figure 3
The ten-quark $Δ B = 2$ operator that results from the leading $(u_{R} d_{R} b_{R})^{2}$ operator after integrating out the $b$ quarks. The crosses represent chirality-flipping $b$ quark mass insertions. We use $⟨ {\bar{u}}_{L} u_{R} ⟩$ to indicate the pairs of light quark fields that can be replaced by the chiral condensate when matching onto the long distance theory relevant for dinucleon decay.
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Figure 4
Upper limits on $M_{12}$ as functions of $m_{ϕ}$ that result from collider searches for dijet resonances and jets plus missing energy, assuming the dominance of the product of couplings $g_{u d} y_{i d^{'}}$ indicated, where $u$ and $d^{(')}$ label generic up- and down-type quarks, respectively. We have taken $Δ m_{B} = m_{B} - m_{χ} = 200 MeV$ . Top: The limits when $y_{i d}$ or $y_{i s}$ are dominant. Bottom: The limits when $y_{i b}$ is dominant. Solid curves show the limits in the case where the charge $2 / 3$ quark involved is $u$ while dashed lines show the limit in the case of the $c$ quark.
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Figure 5
$η_{B} = (n_{B} - n_{\bar{B}}) / s$ (solid, black) as a function of the temperature or time from a numerical solution of Eqs. (39), (40), and (47) for parameters relevant to the $Ω_{c b}^{0} - {\bar{Ω}}_{c b}^{0}$ system: $m_{B} = 7 GeV$ , $Γ_{B} = 3 \times 10^{- 12} GeV$ , $| M_{12} | = 3 \times 10^{- 15} GeV$ , $| Γ_{12} / M_{12} | = 0.3$ , $\arg (M_{12}^{*} Γ_{12}) = π / 2$ , $m_{χ_{3}} = 7.5 GeV$ , $Γ_{χ_{3}} = 3 \times 10^{- 23} GeV$ , and ${Br}_{χ_{3} \to B} = 0.35$ . We have taken the rate for heavy baryon scattering on the plasma from Eq. (52) and the annihilation cross section to be 400 mb. This can be compared against the value of $η_{B}$ (solid, gray) from a solution of Eqs. (39), (40), and (59) as well as using the sudden decay approximation (dashed, gray) in Eq. (65). Also shown are the ratio of the number density of $χ_{3}$ to the entropy density (multiplied by $10^{- 4}$ , solid, orange) and the ratio of the $B$ plus $\bar{B}$ number densities to the entropy density (solid, purple). The dashed purple line shows the equilibrium $B$ and $\bar{B}$ density (in units of the entropy density). The measured value of $η_{B} = 8.8 \times 10^{- 11}$ is given by the solid red line.
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Figure 6
The temperature dependence of the rates involved in the numerical solution of Eqs. (39), (40), and (47). The parameters are the same as in Fig. 5. In orange, from top to bottom are the scattering, annihilation, and Hubble rates. The purple lines indicate the rates relevant to the $B − \bar{B}$ system itself, $Γ_{B}$ , $| M_{12} |$ , and $| Γ_{12} |$ , from top to bottom, respectively.
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