= Solution
The <SU(5) grand unified theory> has <simply connected space> $G=SU(5)$ and a connected <Standard Model> subgroup. More precisely that subgroup is $(SU(3)\times SU(2)\times U(1))/\mathbb Z_6$; the product notation suppresses a finite central quotient. The <long exact sequence of homotopy groups of a fibration> $H\to G\to G/H$ gives
$$
\pi_2(G/H)\simeq\pi_1(H)\simeq\mathbb Z,\qquad
\pi_1(G/H)\simeq\pi_0(H)=0.
$$
Thus stable <magnetic monopoles> form, whereas this transition does not require walls or strings. The <monopole core and mass scales in an SU(5) transition> are set by the massive gauge and <scalar fields>:
$$
\boxed{r_V\sim(g\eta)^{-1},\qquad r_\phi\sim(\sqrt\lambda\eta)^{-1},\qquad
M_M\sim\frac{4\pi\eta}{g}\times\text{an order-one profile factor}.}
$$
For order-one couplings, the core size is of order $\eta^{-1}$ and the mass is of order $\eta$ up to the often substantial factor $4\pi/g$. These heavy objects are nonrelativistic soon after formation and can survive as stable relics.
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