Limits on sterile neutrino contributions to neutrinoless double beta decay

Nuclear matrix elements (NME) for exchange of arbitrary mass neutrinos are calculated in the interacting boson model (IBM-2). By combining the NME with the phase space factors (PSF), expected half-lives for neutrinos of mass $m_N$ and coupling $U_{eN}$ are estimated. Limits on sterile neutrinos with masses in the eV, keV, MeV-GeV, and TeV range are given.

Figure 1

IBM-2 NMEs for neutrinos of arbitrary mass plotted as a function of $m_N$ in (a) ${}^{76}\mathrm{Ge}$, (b) ${}^{130}\mathrm{Te}$, and (c) ${}^{136}\mathrm{Xe}$. Blue squares represent the exact calculation for $m_N=0.001\mathrm{GeV}$, 0.01 GeV, 0.1 GeV, 1 GeV, 10 GeV, joined together by a Mathematica interpolating formula. The curve is obtained using the simple formula (9).

Figure 2

Comparison between IBM-2 (Argonne SRC) (red), QRPA-Tü (Argonne SRC) [9] (blue), and ISM (UCOM SRC) (green) NMEs for neutrinos of arbitrary mass plotted as a function of $m_N$ in (a) ${}^{76}\mathrm{Ge}$, (b) ${}^{130}\mathrm{Te}$, and (c) ${}^{136}\mathrm{Xe}$.

Figure 3

Expected half-life for a single neutrino of mass $m_N$ with coupling $U_{eN}^2=10^{-2}–10^{-8}$ and $g_A=1.269$ for (a) ${}^{76}\mathrm{Ge}$, (b) ${}^{130}\mathrm{Te}$, and (c) ${}^{136}\mathrm{Xe}$. Blue squares represent the exact calculation for $m_N=0.001\mathrm{GeV}$, 0.01 GeV, 0.1 GeV, 1 GeV, 10 GeV. The smooth curve is obtained using the simple formula (9). The experimental limits from GERDA [17], CUORE-0 [18], KamLAND-Zen [19], and EXO [20] are also shown. The excluded zone is that below these limits.

Figure 4

Excluded values of ${|U_{eN}|}^2$ and $m_N$ in the $m_N\text{−}{|U_{eN}|}^2$ plane, for $g_A=1.269$. For each experiment, GERDA [17], CUORE-0 [18], KamLAND-Zen [19], and EXO [20], a band of values is given, corresponding to our error estimate.

Figure 5

Excluded region for different values of $g_A$, for ${}^{136}\mathrm{Xe}$ (EXO collaboration [20]).

Figure 6

Current limits for $⟨m_{N,\text{light}}⟩$ from the CUORE-0 [18], IGEX [25], NEMO-3 [26], KamLAND-Zen [19], EXO [20], and GERDA [17] experiments, and IBM-2 Argonne SRC NMEs and $g_A=1.269$. The value of Ref. [27] is shown by $X$. The figure is in semilogarithmic scale. Red shows the normal hierarchy and green the inverted hierarchy. In this figure the scenario suggested in [2], relevant to LSND and reactor anomaly, is considered.