Twin mechanism for baryon and dark matter asymmetries

In the context of twin Higgs models, we study a simple mechanism that simultaneously generates asymmetries in the dark and visible sector through the out-of-equilibrium decay of a TeV-scale particle charged under a combination of baryon and twin baryon number. We predict the dark matter to be a 5 GeV twin baryon, which is easy to achieve because of the similarity between the two confinement scales. Dark matter is metastable and can decay to three quarks, yielding indirect detection signatures. The mechanism requires the introduction of a new colored particle, typically within the reach of the LHC, of which we study the rich collider phenomenology, including prompt and displaced dijets, multijets, monojets and monotops.

Figure 1

Tree-level and one-loop diagrams for the decays ${\mathrm{\Psi }}_1\to \overline{q}\varphi$ (which will be followed by $\varphi \to \overline{q}\overline{q}$). Conjugate diagrams contribute to ${\overline{\mathrm{\Psi }}}_1\to q{\varphi }^{*}$. The interference between the diagrams with on-shell particles in the loop gives a nonzero imaginary part. Similar diagrams for ${\mathrm{\Psi }}_1\to \tilde{q}{\tilde{\varphi }}^{*}$ (with twin final states and SM intermediate states) generate the twin asymmetry.

Figure 2

Tree-level and two-loop diagrams for the decay ${\mathrm{\Psi }}_1\to \overline{q}\overline{q}\overline{q}$. Conjugate diagrams give ${\overline{\mathrm{\Psi }}}_1\to qqq$. The interference between the two diagrams with on-shell particles in the loop gives a nonzero imaginary part. Similar diagrams for ${\mathrm{\Psi }}_1\to \tilde{q}\tilde{q}\tilde{q}$ generate the twin asymmetry.

Figure 3

LHC and dark matter lifetime constraints on the one-loop model for baryogenesis with universal couplings and having set $M_1=1\mathrm{TeV}$, $M_2=10M_1$. Shaded regions are excluded by the different experimental signatures. LHC constraints on a pair-produced scalar $\varphi$ decaying into jets are shown in magenta, blue and orange for prompt [50, 51], displaced [53] and collider-stable [57] decays, respectively. The displaced exclusions are adapted from Ref. [53] and agree well with Ref. [54]; the lighter blue area corresponds to changing the acceptances up/down by 1.5. Dashed lines saturate the DM lifetime bound ${\tau }_{\mathrm{DM}}\ge 10^{25}\sec$: for each value of the asymmetry parameter $\epsilon$, regions below the dashed line are excluded. The DM lifetime constraints are shown assuming decays predominantly mediated by ${\mathrm{\Psi }}_1$ and ${\kappa }_1={\kappa }_2$ (corresponding to nonthermal ${\mathrm{\Psi }}_1$): for the thermal case, the constraints are slightly weaker.

Figure 4

LHC and dark matter lifetime constraints when a flavor hierarchy is present. The baryon asymmetry is created at one loop at the left of the dashed line marking $m_{\varphi }=M_1$ and at two loop on the right. We fix ${\kappa }_{2;3}=1$, $M_2=2M_1$ and take $M_1=700\mathrm{GeV}$ (left) or $M_1=1\mathrm{TeV}$ (right). In the green regions, the baryon asymmetry is too small. Curved dashed lines are contours of ${\tau }_{\mathrm{DM}}=10^{25}\sec$ for the corresponding values of $\mathcal{F}\mathcal{R}$, from Eq. (26). For each value of $\mathcal{F}\mathcal{R}$, the region above the corresponding line is excluded. The largest coupling ${\lambda }_{JK}$ involves $q_J{q}_K=bs$ for an up-type $\varphi$, or $tb$ for a down-type $\varphi$. For an up-type $\varphi$, the magenta and blue regions are excluded by searches for paired [50, 51] and single [48, 49] dijet resonances, while there are no LHC constraints for down-type scalars.

Figure 5

Diagrams for twin neutron decays to three SM quarks and up to one twin meson. Square vertices indicate $\tilde{B}$-violating interactions in Eq. (a7), while the round vertex is a $\tilde{B}$-conserving interaction with a twin meson from Eq. (a2). In the last diagram, ${\tilde{B}}^{\prime }$ indicates an intermediate twin baryon, e.g. ${\tilde{B}}^{\prime }={\tilde{\mathrm{\Lambda }}}^0$.

Figure 6

Same as Fig. 3, but including the constraints from $\mathrm{\Delta }{N}_{\text{eff}}$ (in red) on the one-loop model. For consistency with Fig. 3, we showed the constraints from nonthermal ${\mathrm{\Psi }}_1$ production, Eq. (b9).

Figure 7

Same as Fig. 4, but including the constraints from $\mathrm{\Delta }{N}_{\text{eff}}$ (in red) on the two-loop model with hierarchical couplings.