View source for Calabi–Yau manifold

{{short description|Riemannian manifold with SU(n) holonomy}}
{{redirect|Calabi–Yau|the play by Susanna Speier|Calabi-Yau (play)}}
{{more footnotes needed|date=July 2018}}
[[File:CalabiYau5.jpg|thumb|A 2D slice of a 6D Calabi–Yau quintic manifold.]]
In [[algebraic geometry|algebraic]] and [[differential geometry]], a '''Calabi&ndash;Yau manifold''', also known as a '''Calabi&ndash;Yau space''', is a particular type of [[manifold]] which has certain properties, such as [[Ricci flat]]ness, yielding applications in [[theoretical physics]]. Particularly in [[superstring theory]], the extra dimensions of [[spacetime]] are sometimes conjectured to take the form of a 6-dimensional Calabi&ndash;Yau manifold, which led to the idea of  [[Mirror symmetry (string theory)|mirror symmetry]]. Their name was coined by {{harvtxt|Candelas|Horowitz|Strominger|Witten|1985}}, after {{harvs|txt|first= Eugenio|last=Calabi|authorlink= Eugenio Calabi|year1=1954|year2=1957}}, who first conjectured that such surfaces might exist, and {{harvs|txt|authorlink=Shing-Tung Yau|first=Shing-Tung|last= Yau|year=1978}}, who proved the [[Calabi conjecture]].

Calabi&ndash;Yau manifolds are [[complex manifold]]s that are generalizations of [[K3 surface]]s in any number of [[complex dimension]]s (i.e. any even number of real [[dimension]]s). They were originally defined as compact [[Kähler manifold]]s with a vanishing first [[Chern class]] and a Ricci-flat metric, though many other similar but inequivalent definitions are sometimes used.

==Definitions==
The motivational definition given by [[Shing-Tung Yau]] is of a compact [[Kähler manifold]] with a vanishing first Chern class, that is also Ricci flat.{{sfnp|Yau|Nadis|2010}}

There are many other definitions of a Calabi&ndash;Yau manifold used by different authors, some inequivalent. This section summarizes some of the more common definitions and the relations between them.

A Calabi&ndash;Yau <math>n</math>-fold or Calabi&ndash;Yau manifold of (complex) dimension <math>n</math> is sometimes defined as a compact <math>n</math>-dimensional Kähler manifold <math>M</math> satisfying one of the following equivalent conditions: 
* The [[canonical bundle]] of <math>M</math> is trivial.
* <math>M</math> has a holomorphic <math>n</math>-form that vanishes nowhere.
* The [[structure group]] of the [[tangent bundle]] of <math>M</math> can be reduced from <math>U(n)</math>, the [[unitary group]], to <math>SU(n)</math>, the [[special unitary group]].
* <math>M</math> has a Kähler metric with global [[holonomy]] contained in [[SU(n)|<math>SU(n)</math>]].

These conditions imply that the first integral Chern class <math>c_1(M)</math> of <math>M</math> vanishes.  Nevertheless, the converse is not true. The simplest examples where this happens are [[hyperelliptic surface]]s, finite quotients of a complex torus of complex dimension 2, which have vanishing first integral Chern class but non-trivial canonical bundle.

For a compact <math>n</math>-dimensional Kähler manifold <math>M</math> the following conditions are equivalent to each other, but are weaker than the conditions above, though they are sometimes used as the definition of a Calabi&ndash;Yau manifold:
* <math>M</math> has vanishing first real Chern class.
* <math>M</math> has a Kähler metric with vanishing Ricci curvature.
* <math>M</math> has a Kähler metric with local [[holonomy]] contained in [[SU(n)|<math>SU(n)</math>]].
*  A positive power of the [[canonical bundle]] of <math>M</math> is trivial.
* <math>M</math> has a finite cover that has trivial canonical bundle.
* <math>M</math> has a finite cover that is a product of a torus and a [[simply connected space|simply connected]] manifold with trivial canonical bundle.

If a compact Kähler manifold is simply connected, then the weak definition above is equivalent to the stronger definition. [[Enriques surface]]s give examples of complex manifolds that have Ricci-flat metrics, but their canonical bundles are not trivial, so they are Calabi–Yau manifolds according to the second but not the first definition above. On the other hand, their double covers are Calabi–Yau manifolds for both definitions (in fact, K3 surfaces).

By far the hardest part of proving the equivalences between the various properties above is proving the existence of Ricci-flat metrics. This follows from Yau's proof of the [[Calabi conjecture]], which implies that a compact Kähler manifold with a vanishing first real Chern class has a Kähler metric in the same class with vanishing Ricci curvature. (The class of a Kähler metric is the cohomology class of its associated 2-form.) Calabi showed  such  a metric is unique.

There are  many other inequivalent definitions of Calabi–Yau manifolds that are sometimes used, which differ in the following ways (among others):
* The first Chern class may vanish as an integral class or as a real class.
* Most definitions assert that Calabi–Yau manifolds are compact, but some allow them to be non-compact. In the generalization to non-compact manifolds, the difference <math>(\Omega\wedge\bar\Omega - \omega^n/n!)</math> must vanish asymptotically. Here, <math>\omega</math> is the Kähler form associated with the Kähler metric, <math>g</math>.{{sfnp|Tian|Yau|1991}}
* Some definitions put restrictions on the [[fundamental group]] of a Calabi–Yau manifold, such as demanding that it be finite or trivial. Any Calabi–Yau manifold has a finite cover that is the product of a torus and a simply-connected Calabi–Yau manifold.
* Some definitions require that the holonomy be exactly equal to <math>SU(n)</math> rather than a subgroup of it, which implies  that the [[Hodge number]]s <math>h^{i,0}</math> vanish for <math>0 < i < \dim(M)</math>. Abelian surfaces have a Ricci flat metric with holonomy strictly smaller than <math>SU(2)</math> (in fact trivial) so are not Calabi–Yau manifolds according to such definitions.
* Most definitions assume that a Calabi–Yau manifold has a Riemannian metric, but some treat them as complex manifolds without a metric.
* Most definitions assume the manifold is non-singular, but some allow mild singularities. While the Chern class fails to be well-defined for singular Calabi–Yau's, the canonical bundle and canonical class may  still be defined if all the singularities are [[Gorenstein scheme|Gorenstein]], and so may be used to extend the definition of a smooth Calabi–Yau manifold to a possibly singular Calabi–Yau variety.

==Examples==
The fundamental fact is that any smooth [[algebraic variety]] embedded in a [[projective space]] is a Kähler manifold, because there is a natural [[Fubini–Study metric]] on a projective space which one can restrict to the algebraic variety. By definition, if ω is the Kähler metric on the algebraic variety X and the canonical bundle  K<sub>X</sub> is trivial, then X is Calabi&ndash;Yau. Moreover, there is unique Kähler metric ω on X such that [''ω''<sub>0</sub>]&nbsp;=&nbsp;[''ω'']&nbsp;∈&nbsp;''H''<sup>2</sup>(''X'','''R'''), a fact which was conjectured by [[Eugenio Calabi]] and proved by [[Shing-Tung Yau]] (see [[Calabi conjecture]]).

=== Calabi–Yau algebraic curves ===
In one complex dimension, the only compact examples are [[torus|tori]], which form a one-parameter family. The Ricci-flat metric on a torus is actually a [[flat metric]], so that the [[holonomy]] is the trivial group SU(1). A one-dimensional Calabi&ndash;Yau manifold is a complex [[elliptic curve]], and in particular, [[algebraic variety|algebraic]].

=== CY algebraic surfaces ===
In two complex dimensions, the [[K3 surface]]s furnish the only compact simply connected Calabi&ndash;Yau manifolds. These can be constructed as quartic surfaces in <math>\mathbb{P}^3</math>, such as the complex algebraic variety defined by the vanishing locus of

<blockquote><math>x_0^4 + x_1^4 + x_2^4 + x_3^4 = 0</math> for <math>[x_0:x_1:x_2:x_3] \in \mathbb{P}^3</math></blockquote>

Other examples can be constructed as elliptic fibrations,<ref>{{cite arXiv|last=Propp|first=Oron Y.|date=2019-05-22|title=Constructing explicit K3 spectra|class=math.AT|page=4|eprint=1810.08953}}</ref> as quotients of abelian surfaces,<ref>{{cite journal|last=Szymik|first=Markus|date=2020-02-12|title=K3 spectra|journal=Bulletin of the London Mathematical Society|volume=42|pages=137–148|doi=10.1112/blms/bdp106|arxiv=2002.04879|s2cid=1070427}}</ref> or as [[complete intersection]]s.

Non simply-connected examples are given by [[abelian surface]]s, which are real four tori <math>\mathbb{T}^4</math> equipped with a complex manifold structure. [[Enriques surface]]s and [[hyperelliptic surface]]s have first Chern class that vanishes as an element of the real cohomology group, but not as an element of the integral cohomology group, so Yau's theorem about the existence of a Ricci-flat metric still applies to them but they are sometimes not considered to be Calabi&ndash;Yau manifolds. Abelian surfaces are sometimes excluded from the classification of being Calabi&ndash;Yau, as their holonomy (again the trivial group) is a [[subgroup|proper subgroup]] of SU(2), instead of being isomorphic to SU(2). However, the [[Enriques surface]] subset do not conform entirely to the SU(2) subgroup in the [[String theory landscape]].

=== CY threefolds ===
In three complex dimensions, classification of the possible Calabi&ndash;Yau manifolds is an open problem, although Yau suspects that there is a finite number of families (albeit a much bigger number than his estimate from 20 years ago).  In turn, it has also been conjectured by [[Miles Reid]] that the number of topological types of Calabi–Yau 3-folds is infinite, and that they can all be transformed continuously ( through certain mild singularizations such as [[conifold]]s) one into another&mdash;much as [[Riemann surface]]s can.<ref>{{cite journal | last1 = Reid | first1 = Miles | author-link = Miles Reid | year = 1987 | title = The Moduli space of 3-folds with ''K''&nbsp;=&nbsp;0 may nevertheless be irreducible | journal = [[Mathematische Annalen]] | volume = 278 | issue = 1–4 | pages = 329–334 | doi=10.1007/bf01458074| s2cid = 120390363 }}</ref>  One example of a three-dimensional Calabi&ndash;Yau manifold is a non-singular [[quintic threefold]] in [[complex projective space|'''CP'''<sup>4</sup>]], which is the [[algebraic variety]] consisting of all of the zeros of a homogeneous quintic [[polynomial]] in the homogeneous coordinates of the '''CP'''<sup>4</sup>.  Another example is a smooth model of the [[Barth–Nieto quintic]]. Some discrete quotients of the quintic by various '''Z'''<sub>5</sub> actions are also Calabi&ndash;Yau and have received a lot of attention in the literature.  One of these is related to the original quintic by [[mirror symmetry (string theory)|mirror symmetry]].

For every positive integer ''n'', the [[zero set]], in the homogeneous coordinates of the complex projective space '''CP'''<sup>''n''+1</sup>, of a non-singular homogeneous degree ''n''&nbsp;+&nbsp;2 polynomial in ''n''&nbsp;+&nbsp;2 variables  is a compact Calabi–Yau ''n''-fold.  The case ''n''&nbsp;=&nbsp;1 describes an elliptic curve, while for ''n''&nbsp;=&nbsp;2 one obtains a K3 surface.

More generally, Calabi–Yau varieties/orbifolds can be found as weighted complete intersections in a [[weighted projective space]]. The main tool for finding such spaces is the [[adjunction formula]].

All [[hyper-Kähler manifold]]s are Calabi–Yau manifolds.

==== Constructed from algebraic curves ====
For an algebraic curve <math>C</math> a quasi-projective Calabi-Yau threefold can be constructed<ref>{{cite arXiv |last=Szendroi |first=Balazs |date=2016-04-27 |title=Cohomological Donaldson-Thomas theory |class=math.AG |eprint=1503.07349 }}</ref> as the total space <math>V = \text{Tot}(\mathcal{L}_1\oplus\mathcal{L}_2)</math> where <math>\mathcal{L}_1\otimes\mathcal{L}_2 \cong \omega_C</math>. For the canonical projection <math>p: V \to C</math> we can find the relative tangent bundle <math>T_{V/C}</math> is <math>p^*(\mathcal{L}_1\oplus\mathcal{L}_2)</math> using the relative tangent sequence

<blockquote><math>0 \to T_{V/C} \to T_V \to p^*T_C \to 0</math></blockquote>

and observing the only tangent vectors in the fiber which are not in the pre-image of <math>p^*T_C</math> are canonically associated with the fibers of the vector bundle. Using this, we can use the relative cotangent sequence

<blockquote><math>0 \to p^*\Omega_C \to \Omega_V \to \Omega_{V/C} \to 0</math></blockquote>

together with the properties of wedge powers that

<blockquote><math>\omega_V = \bigwedge^3\Omega_V \cong f^*\omega_C\otimes\bigwedge^2\Omega_{V/C}</math></blockquote>

and <math>\Omega_{V/C} \cong \mathcal{L}_1^*\oplus\mathcal{L}_2^*</math> giving the triviality of <math>\omega_V</math>.

==== Constructed from algebraic surfaces ====
Using a similar argument as for curves, the total space <math>\text{Tot}(\omega_S)</math> of the canonical sheaf <math>\omega_S</math> for an algebraic surface <math>S</math> forms a Calabi-Yau threefold. A simple example is <math>\text{Tot}(\mathcal{O}_{\mathbb{P}^2}(-3))</math> over projective space.

==Applications in superstring theory==

Calabi&ndash;Yau manifolds are important in [[superstring theory]].  Essentially, Calabi&ndash;Yau manifolds are shapes that satisfy the requirement of space for the six "unseen" spatial dimensions of string theory, which may be smaller than our currently observable lengths as they have not yet been detected. A popular alternative known as [[large extra dimension]]s, which often occurs in [[braneworld]] models, is that the Calabi&ndash;Yau is large but we are confined to a small subset on which it intersects a [[D-brane]]. Further extensions into higher dimensions are currently being explored with additional ramifications for [[general relativity]].

In the most conventional superstring models, ten conjectural dimensions in [[string theory]] are supposed to come as four of which we are aware, carrying some kind of [[fibration]] with fiber dimension six. [[Compactification (physics)|Compactification]] on Calabi&ndash;Yau ''n''-folds are important because they leave some of the original [[supersymmetry]] unbroken. More precisely, in the absence of [[Ramond&ndash;Ramond field|fluxes]], compactification on a Calabi&ndash;Yau 3-fold (real dimension 6) leaves one quarter of the original supersymmetry unbroken if the [[holonomy]] is the full SU(3).

More generally, a flux-free compactification on an ''n''-manifold with holonomy SU(''n'') leaves 2<sup>1−''n''</sup> of the original supersymmetry unbroken, corresponding to 2<sup>6−''n''</sup> supercharges in a compactification of [[type IIA supergravity]] or 2<sup>5−''n''</sup> supercharges in a compactification of type I.  When fluxes are included the supersymmetry condition instead implies that the compactification manifold be a [[generalized Calabi&ndash;Yau]], a notion introduced by {{harvtxt|Hitchin|2003}}.  These models are known as [[Compactification (physics)#Flux compactification|flux compactification]]s.

[[F-theory]] compactifications on various Calabi&ndash;Yau four-folds provide physicists with a method to find a large number of classical solutions in the so-called [[string theory landscape]].

Connected with each hole in the Calabi–Yau space is a group of low-energy string vibrational patterns. Since string theory states that our familiar elementary particles correspond to low-energy string vibrations, the presence of multiple holes causes the string patterns to fall into multiple groups, or [[Generation (particle physics)|families]]. Although the following statement has been simplified, it conveys the logic of the argument: if the Calabi–Yau has three holes, then three families of vibrational patterns and thus three families of particles will be observed experimentally.

Logically, since strings vibrate through all the dimensions, the shape of the curled-up ones will affect their vibrations and thus the properties of the elementary particles observed. For example, [[Andrew Strominger]] and [[Edward Witten]] have shown that the masses of particles depend on the manner of the intersection of the various holes in a Calabi–Yau. In other words, the positions of the holes relative to one another and to the substance of the Calabi–Yau space was found by Strominger and Witten to affect the masses of particles in a certain way. This is true of all particle properties.<ref>{{cite web|url=http://library.thinkquest.org/27930/stringtheory5.htm|title=The Shape of Curled-Up Dimensions|archive-url=https://web.archive.org/web/20060913014709/http://library.thinkquest.org/27930/stringtheory5.htm|archive-date=September 13, 2006}}</ref>

== Calabi-Yau algebra ==
A '''Calabi–Yau algebra''' was introduced by [[Victor Ginzburg]] to transport the geometry of a Calabi–Yau manifold to [[noncommutative algebraic geometry]].<ref>{{cite arXiv |first1=Victor |last1=Ginzburg |title=Calabi-Yau algebras |year=2007 |eprint=math/0612139}}</ref><ref>{{cite arXiv|first1=Travis|last1=Schedler|title=Deformations of algebras in noncommutative geometry|year=2019|class=math.RA |eprint=1212.0914}}</ref>

==In popular culture==
{{In popular culture|date=January 2025}}
* The Calabi-Yau manifold was the subject of a paper coauthored by [[Sheldon Cooper]] in the episode 2 of the seventh season in ''[[Young Sheldon]]''.
* Imagery based on Calabi-Yau manifolds was used in [[Judgment Day (3 Body Problem)|episode 5]] of the TV series ''[[3 Body Problem (TV series)|3 Body Problem]]'' in order to illustrate the high-dimensional abilities of the San-Ti alien civilization.
* In [[Half-Life 2]], Dr. Mossman describes teleporters as working via a 'String-based' technology using 'the Calabi-Yau model.'

==See also==
*[[Quintic threefold]]
*[[G2 manifold]]

==References==
{{reflist}}
*{{Citation|last=Calabi|first=Eugenio|author-link=Eugenio Calabi|chapter=The space of Kähler metrics|title=Proc. Internat. Congress Math. Amsterdam| year=1954|volume=2|pages=206&ndash;207|chapter-url=http://mathunion.org/ICM/ICM1954.2/|url-status = dead|archive-url=https://web.archive.org/web/20110717144747/http://mathunion.org/ICM/ICM1954.2/|archive-date=2011-07-17}}
*{{Citation | last1=Calabi | first1=Eugenio | editor1-last=Fox | editor1-first=Ralph H. | editor1-link=Ralph Fox|editor2-last=Spencer | editor2-first=Donald C. | editor2-link=Donald C. Spencer  |editor3-last=Tucker | editor3-first=Albert W. |editor3-link=Albert W. Tucker| title=Algebraic geometry and topology. A symposium in honor of S. Lefschetz | url=https://books.google.com/books?id=n_ZQAAAAMAAJ | publisher=[[Princeton University Press]] | series=Princeton Mathematical Series | mr=0085583 | year=1957 | volume=12 | chapter=On Kähler manifolds with vanishing canonical class | pages=78–89| isbn=9780691079073 }}
*{{citation|last1=Candelas|first1=Philip|last2=Horowitz|first2=Gary|last3=Strominger|first3=Andrew|last4=Witten|first4=Edward|year=1985|title=Vacuum configurations for superstrings|journal=Nuclear Physics B|volume=258|pages=46–74|doi=10.1016/0550-3213(85)90602-9|url=http://www-lib.kek.jp/cgi-bin/img_index?8504007|archive-url=https://archive.today/20121220035310/http://www-lib.kek.jp/cgi-bin/img_index?8504007|url-status=dead|archive-date=December 20, 2012|bibcode=1985NuPhB.258...46C}}
*{{Citation | author-link=Nigel Hitchin | last1=Hitchin | first1=Nigel | title=Generalized Calabi&ndash;Yau manifolds | arxiv=math.DG/0209099 | mr=2013140 | year=2003 | journal=The Quarterly Journal of Mathematics  | volume=54 | issue=3 | pages=281–308 | doi=10.1093/qmath/hag025| citeseerx=10.1.1.237.8935 }}
*{{Citation| first1=Gang| last1=Tian| first2=Shing-Tung| last2=Yau| title=Complete Kähler manifolds with zero Ricci curvature, II| journal=Invent. Math.| volume=106| issue=1| pages=27–60|  year=1991| doi=10.1007/BF01243902|bibcode = 1991InMat.106...27T | s2cid=122638262}}
*{{Citation | last1=Yau | first1=Shing Tung | title=On the Ricci curvature of a compact Kähler manifold and the complex Monge-Ampère equation. I | doi=10.1002/cpa.3160310304  | mr=480350 | year=1978 | journal=[[Communications on Pure and Applied Mathematics]] | volume=31 | issue=3 | pages=339–411 }}
*{{Citation | last1=Yau | first1=Shing-Tung | title=Geometry, analysis, and algebraic geometry: forty years of the Journal of Differential Geometry | publisher=Int. Press | location= Somerville, Massachusetts | series=Surveys in Differential Geometry | mr=2537089 | year=2009a | volume=13 | chapter=A survey of Calabi–Yau manifolds | pages=277–318 | doi=10.4310/SDG.2008.v13.n1.a9| doi-access=free }}
*{{Citation |last1=Yau |first1=Shing-Tung |last2=Nadis |first2=Steve |title=The Shape of Inner Space |publisher=Basic Books |year=2010 |isbn=978-0-465-02023-2}}

==Further reading==
*{{Citation | last1=Besse | first1=Arthur L. | author-link=Arthur Besse|title=Einstein manifolds | publisher=[[Springer-Verlag]] | location=Berlin, New York | series=Ergebnisse der Mathematik und ihrer Grenzgebiete (3)| volume=10 | isbn=978-3-540-15279-8 | year=1987 | oclc=13793300 |ref=none}}
*{{Citation|last1=Bini | last2=Iacono| title=Diffeomorphism Classes of Calabi–Yau Varieties | url=http://www.seminariomatematico.unito.it/rendiconti/73-12/9.pdf | bibcode=2016arXiv161204311B| year=2016| arxiv=1612.04311|ref=none}}
*{{citation |last=Chan |first=Yat-Ming |year=2004 |arxiv=math/0410260 |title=Desingularizations of Calabi-Yau 3-folds with a conical singularity |bibcode=2004math.....10260C |ref=none}}
*{{Citation | last=Greene|first= Brian|author-link=Brian Greene| title=String theory on Calabi–Yau manifolds|series=Fields, strings and duality (Boulder, CO, 1996)|pages=543–726|publisher= World Sci. Publ.|location=River Edge, NJ|year=1997|arxiv=hep-th/9702155v1|mr=1479700|bibcode=1997hep.th....2155G|ref=none}}
*{{Citation | last1=Gross | first1=M. | last2=Huybrechts | first2=D. | last3=Joyce | first3=Dominic | author3-link=Dominic Joyce | title=Calabi&ndash;Yau manifolds and related geometries | publisher=[[Springer-Verlag]] | location=Berlin, New York | series=Universitext | isbn=978-3-540-44059-8 | mr=1963559 | year=2003 | oclc=50695398 | doi=10.1007/978-3-642-19004-9| doi-access=free |ref=none}}
*{{Citation |last=He |first=Yang-Hu |year=2021 |title=The Calabi–Yau Landscape: From Geometry, to Physics, to Machine Learning |place=Switzerland |publisher=Springer International Publishing |isbn=978-3-030-77562-9 |ref=none}}
*{{Citation | last1=Hübsch | first1=Tristan | title=Calabi&ndash;Yau Manifolds: a Bestiary for Physicists | publisher=[[World Scientific]] | location=Singapore, New York | isbn=978-981-02-1927-7 | year=1994 | oclc=34989218 | url=http://www.worldscibooks.com/physics/1410.html | access-date=2009-02-04 | archive-url=https://web.archive.org/web/20100113083908/http://worldscibooks.com/physics/1410.html | archive-date=2010-01-13 |url-status = dead |ref=none}}
*{{Citation | last1=Joyce | first1=Dominic | author1-link=Dominic Joyce | title=Compact Manifolds with Special Holonomy | publisher=[[Oxford University Press]] | isbn=978-0-19-850601-0 | year=2000 | oclc=43864470 |ref=none}}
*{{Citation| first1=Gang| last1=Tian| first2=Shing-Tung| last2=Yau|title=Complete Kähler manifolds with zero Ricci curvature, I| journal=J. Amer. Math. Soc.| volume=3| issue=3| pages=579–609|  year=1990|doi=10.2307/1990928| jstor=1990928 |ref=none}}
*{{citation|last=Yau|first=S. T. |title=Calabi&ndash;Yau manifold|year=2009b |journal=Scholarpedia|volume=4 |issue=8 |page=6524 |doi=10.4249/scholarpedia.6524 |bibcode=2009SchpJ...4.6524Y |doi-access=free }} (similar to {{harv|Yau|2009a}})

==External links==
{{Commons category|Calabi-Yau variety}}
{{wikiquote}}
*[http://www.th.physik.uni-bonn.de/th/Supplements/cy.html Calabi&ndash;Yau Homepage] is an interactive reference which describes many examples and classes of Calabi&ndash;Yau manifolds and also the physical theories in which they appear.
*[http://members.wri.com/jeffb/visualization/stringtheory2.shtml Spinning Calabi&ndash;Yau Space video.]
*''[http://demonstrations.wolfram.com/CalabiYauSpace/ Calabi&ndash;Yau Space]'' by Andrew J. Hanson with additional contributions by Jeff Bryant, [[Wolfram Demonstrations Project]].
*{{MathWorld |title=Calabi&ndash;Yau Space |urlname=Calabi-YauSpace}}

=== Beginner articles ===
* [https://indico.cern.ch/event/927781/contributions/3926290/attachments/2101500/3533039/Anderson_CY_Review.pdf An overview of Calabi-Yau Elliptic fibrations]
*Lectures on the [[arxiv:2001.01212|Calabi-Yau Landscape]]
* [[arxiv:1708.07907|Fibrations in CICY Threefolds]] - ([[complete intersection]] Calabi-Yau)

{{String theory topics}}

{{DEFAULTSORT:Calabi-Yau manifold}}
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