Probing radiative neutrino mass generation through monotop production

We present a generalization of a model where the right-handed up-type quarks serve as messengers for neutrino mass generation and as a portal for dark matter. Within this framework, the Standard Model is extended with a single Majorana neutrino, a colored electroweak-singlet scalar, and a colored electroweak-triplet scalar. We calculate the relic abundance of dark matter and show that we can match the latest experimental results. Furthermore, the implications from the scattering between nuclei and the dark matter candidate are studied, and we implement the latest experimental constraints arising from flavor changing interactions, Higgs production and decay, and LHC collider searches for a single jet and jets plus missing energy. In addition, we implement constraints arising from scalar top quark pair production. We also study the production of a single top in association with missing energy and calculate the sensitivity of the LHC to the top quark semileptonic decay mode with the current ${20\mathrm{fb}}^{-1}$ data set at a center-of-mass energy of $\sqrt{s}=8\mathrm{TeV}$. Furthermore, we carry out the analysis to center-of-mass energies of $\sqrt{s}=14\mathrm{TeV}$ with 30 and $300{\mathrm{fb}}^{-1}$ of data.

Figure 1

Interaction channels that lead to a reduction in the relic abundance of $N_R$: Channels consist of annihilation into $u_i{\overline{u}}_j$, $i,j=u,c,t$. A similar $u$-channel graph is not shown.

Figure 2

Thermalized cross section in the $m_{\psi }-M_{N_R}$ plane for $y_{\psi }^{t,u}=0$, $y_{\psi }^c=1$ on the left and $y_{\psi }^{c,u}=0$, $y_{\psi }^t=1$ on the right. The green region corresponds to $⟨\sigma v⟩>3\times 10^{-26}{\mathrm{cm}}^3/\mathrm{s}$, while the dashed black line to $⟨\sigma v⟩=3\times 10^{-26}{\mathrm{cm}}^3/\mathrm{s}$.

Figure 3

Spin-dependent cross section as a function of the Majorana neutrino mass $M_{N_R}$ for $y_{\psi }^u=0.1$. For coupling to protons (left), limits from COUPP [7], PICASSO [8], and SIMPLE [9] are shown in green, red, and blue, respectively, while the spin-dependent cross section for scalar mediator masses of $m_{\psi }=100,400,600\mathrm{GeV}$ are depicted by the solid disks, triangles, and squares, respectively. For coupling to neutrons (right), limits from XENON10 [10] are shown in red.

Figure 4

Same as in Figs. 3 and 3 but with $y_{\psi }^u=0.5$.

Figure 5

Three-loop generation of a Majorana mass for active neutrinos from the $t$ quark. The crosses on the fermion lines indicate mass insertions. The large solid dot at the top of the diagram indicates an effective $\psi \psi \chi \chi$ vertex. Similar diagrams from the $u$ and $c$ quarks will also play a role.

Figure 6

$K^{t,t}$, $K^{t,c}$, and $K^{c,c}$ factors in the $M_{N_R}-m_{\psi }$ plane. (a) Left: $y_{\psi }^t=1$ and $y_{\psi }^c=0.01$. The red and black solid lines correspond to $K^{t,t}=1.5,0.5\mathrm{MeV}$, respectively, while the red and black dashed lines correspond to $K^{t,c}=0.12,0.04\mathrm{eV}$, respectively. (b) Right: $y_{\psi }^t=0.01$ and $y_{\psi }^c=1$. The red and black solid lines correspond to $K^{t,t}=0.15,0.05\mathrm{eV}$, respectively, while the red and black dashed lines correspond to $K^{t,c}=0.12,0.04\mathrm{eV}$, respectively. On the right, we see that $K^{c,c}$ is of the same order as $K^{t,t}$ and $K^{t,c}$ in black and red dotted lines.

Figure 7

One-loop diagrams for $\mu (p)\to e(p^{\prime })+\gamma (q)$ decays. The arrows indicate fermion charge flow. Main contribution comes from (a) and (b), whereas (c) and (d) are needed to enforce gauge invariance. Similar diagrams from the second-generation quarks are not displayed.

Figure 8

Regions in the $m_{\psi }-{\kappa }_3$ plane consistent with the CMS and ATLAS Higgs data at the $1\sigma$ (light grey) and $2\sigma$ (dark grey) levels.

Figure 9

Leading-order Feynman diagrams lead to jets plus MET final states at the LHC. The diagram on the left, (a), lead to a $t\overline{t}$ plus MET signature and can be constrained by searches for scalar top pair production 9. The diagram on the right, (b), results in a monojet signal from up-type quark gluon fusion.

Figure 10

Leading-order Feynman diagrams that lead to jets plus MET final states at the LHC and that enhance the production rate at large $y_{\psi }^{t,c,u}$. The diagram on the left, (a), contributes to same-sign up-type quark production at the LHC while the one on the right, (b) yields a single jet in association with MET.

Figure 11

Allowed region of parameter space consistent with the density of dark matter as measured by Planck [6] (red solid line) after taking into account all constraints discussed in Sec. 5 for $y_{\psi }^t=1$ and $y_{\psi }^{c,u}=0.1$ on the left and $y_{\psi }^t=1$ and $y_{\psi }^{c,u}=0.01,0.5$ on the right. The region in white is allowed, but our dark matter annihilates too efficiently in the early Universe.

Figure 12

Allowed region of parameter space consistent with the density of dark matter as measured by Planck [6] (red solid line) after taking into account all constraints discussed in Sec. 5 for $y_{\psi }^t=0.4$ and $y_{\psi }^{c,u}=0.01,1$. The region in white is allowed, but the dark matter annihilates too efficiently in the early Universe.

Figure 13

Leading-order Feynman diagram for monotop production at the LHC in association with missing transversed energy carried away by a Majorana neutrino.

Figure 14

Fraction of events as a function of the missing transverse energy $\cancel{E}$ (left) and the lepton’s transverse mass $M_T$ (right). The black solid line represents a scenario within our framework where $m_{\psi }=150\mathrm{GeV}$ and $M_{N_R}=80\mathrm{GeV}$, while the dashed black line represents $m_{\psi }=700\mathrm{GeV}$ and $M_{N_R}=210\mathrm{GeV}$. Both signals were generated using $(y_{\psi }^t,y_{\psi }^c,y_{\psi }^u)=(1,0,0.5)$.

Figure 15

LHC reach with $20{\mathrm{fb}}^{-1}$ at 8 TeV of our semileptonic monotop signal using $(y_{\psi }^t,y_{\psi }^c,y_{\psi }^u)=(1,0,0.5)$ after applying all the cuts described in the text with ${\cancel{E}}_T,M_T>90,110\mathrm{GeV}$ (left) and ${\cancel{E}}_T,M_T>200,120\mathrm{GeV}$ (right). We show three regions where our monotop signal can reach a significance $s=S/\sqrt{S+B}$ of 2, 3, and 5 depicted by the black, blue, and green solid lines, respectively.

Figure 16

LHC reach with $30{\mathrm{fb}}^{-1}$ (left) and $300{\mathrm{fb}}^{-1}$ (right) at 14 TeV of our semileptonic monotop signal using $(y_{\psi }^t,y_{\psi }^c,y_{\psi }^u)=(1,0,0.5)$ and after applying all the cuts described in the text. The three regions where our monotop signal can reach a significance $s=S/\sqrt{S+B}$ of 2, 3, and 5 are depicted by the solid black, blue, and green lines, respectively.

Figure 17

Fraction of events as a function of the transverse momentum of the reconstructed top quark, $p_{T,\text{top}}$. The dashed black line represents a scenario within our framework where $m_{\psi }=700\mathrm{GeV}$ and $M_{N_R}=210\mathrm{GeV}$. Both signals were generated using $(y_{\psi }^t,y_{\psi }^c,y_{\psi }^u)=(1,0,0.5)$.