Conifold

In

cones over a certain base. In physics, in particular in flux compactifications of string theory, the base is usually a five-dimensional

real manifold, since the typically considered conifolds are complex 3-dimensional (real 6-dimensional) spaces.

Overview

Conifolds are important objects in string theory: Brian Greene explains the physics of conifolds in Chapter 13 of his book The Elegant Universe—including the fact that the space can tear near the cone, and its topology can change. This possibility was first noticed by Candelas et al. (1988) and employed by Green & Hübsch (1988) to prove that conifolds provide a connection between all (then) known Calabi–Yau compactifications in string theory; this partially supports a conjecture by Reid (1987) whereby conifolds connect all possible Calabi–Yau complex 3-dimensional spaces.

A well-known example of a conifold is obtained as a deformation limit of a quintic - i.e. a quintic hypersurface in the projective space $\mathbb {CP} ^{4}$ . The space $\mathbb {CP} ^{4}$ has complex dimension equal to four, and therefore the space defined by the quintic (degree five) equations:

z_{1}^{5}+z_{2}^{5}+z_{3}^{5}+z_{4}^{5}+z_{5}^{5}-5\psi z_{1}z_{2}z_{3}z_{4}z_{5}=0

in terms of homogeneous coordinates $z_{i}$ on $\mathbb {CP} ^{4}$ , for any fixed complex $\psi$ , has complex dimension three. This family of quintic hypersurfaces is the most famous example of Calabi–Yau manifolds. If the complex structure parameter $\psi$ is chosen to become equal to one, the manifold described above becomes singular since the derivatives of the quintic polynomial in the equation vanish when all coordinates $z_{i}$ are equal or their

cone whose base is topologically

just.

S^{2}\times S^{3}

In the context of

Type IIA string theory, as originally pointed out by Strominger (1995). As shown by Greene, Morrison & Strominger (1995), this provides the string-theoretic description of the topology-change via the conifold transition originally described by Candelas, Green & Hübsch (1990)

, who also invented the term "conifold" and the diagram

for the purpose. The two topologically distinct ways of smoothing a conifold are thus shown to involve replacing the singular vertex (node) by either a 3-sphere (by way of deforming the complex structure) or a 2-sphere (by way of a "small resolution"). It is believed that nearly all Calabi–Yau manifolds can be connected via these "critical transitions", resonating with Reid's conjecture.

References

Candelas, Philip; Dale, A.M.; Lutken, Andrew; Schimmrigk, Rolf (1988), "Complete intersection Calabi-Yau manifolds", Nuclear Physics B, 298 (3): 493–525,
doi:10.1016/0550-3213(88)90352-5

Reid, Miles (1987), "The moduli space of 3-folds with K=0 may nevertheless be irreducible", Mathematische Annalen, 278 (1–4): 329–334,
S2CID 120390363

Green, Paul; Hübsch, Tristan (1988), "Connecting Moduli Spaces of Calabi-Yau Threefolds", Communications in Mathematical Physics, 119 (3): 431–441,
S2CID 119452483

Candelas, Philip; Green, Paul; Hübsch, Tristan (1990), "Rolling Among Calabi-Yau Vacua", Nuclear Physics B, 330 (1): 49–102,
doi:10.1016/0550-3213(90)90302-T

Strominger, Andrew (1995), "Massless black holes and conifolds in string theory", Nuclear Physics B, 451 (1–2): 96–108,
S2CID 6035714

Greene, Brian; Morrison, David; Strominger, Andrew (1995), "Black hole condensation and the unification of string vacua", Nuclear Physics B, 451 (1–2): 109–120,
S2CID 11145691

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Overview

References

Further reading