# Squashed group manifolds in String Theory exact solutions, brane realization, classical integrability

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### Squashed group manifolds in String Theory

exact solutions, brane realization, classical integrability

Domenico Orlando 数物連携宇宙研究機構

Institute for the Physics and Mathematics of the Universe

National Taiwan University 6 May 2011

Based on:[arXiv:1003.0712, arXiv:1011.1771, arXiv:1104.0738]and work in progress Collaboration with:

I.Kawaguchi (Kyoto),S.Reffert (IPMU), L.Uruchurtu (Imperial College), K.Yoshida (Kyoto)

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### Outline

. .1. Why are we here?

. .2. The main idea . .3. D–brane construction

. .4. Integrability of the Principal Chiral Model . .5. Heterotic construction (or, the S–dual story) . .6. Conclusion

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### Outline

. .1. Why are we here?

. .2. The main idea . .3. D–brane construction

. .4. Integrability of the Principal Chiral Model . .5. Heterotic construction (or, the S–dual story) . .6. Conclusion

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### Squashed geometries

String theory provides a dual description of the same physics: worldsheet andtarget space

In very few cases we can access both and learn from both sides

Most of these cases (ﬂat spacetime, group manifolds, plane waves) have a high degree of symmetry

More symmetry meansmore structure(and simpler analysis)

Can we break part of this symmetry, at the same time preserving the “nice”

structures?

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### Three dimensional gravity

Three–dimensional gravityprovides a simple laboratory for quantum gravity There are no propagating gravitons

There are non-trivial solutions (BTZ black holes) Pure gravity solutions are alwayslocally AdS3

Anti–de Sitter spaces appear innear-horizon geometriesof various D–brane conﬁgurations

AdS3appears as anexact string theory background(Wess–Zumino–Witten model)

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### TMG

Three–dimensional AdS spaces also appear as solutions of topologically massive gravity(TMG)

Stmg(g) = 1 16πG

d3x

−g (

R + 2 2

)

+ μ SCS

for μ̸= 1 the anti–de Sitter solution is unstable, but there aretwo warped solutionswith metric of the type

2− cosh2ω dτ2+ 1 cosh2Θw

(dβ + sinh ω dτ)2]

where Θw is a deformation parameter:

for Θw= 0 this is AdS3 for Θw→ ∞ this is AdS2× S1

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### Today’s talk

Geometryof squashed groups in general (and AdS3 in particular) T–dualityacts on principal ﬁbrations

Type IIsolutions with squashed AdS3and S3 Integrability(without RR ﬁelds)

ExactCFTwith squashed group geometry

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### Outline

. .1. Why are we here?

. .2. The main idea . .3. D–brane construction

. .4. Integrability of the Principal Chiral Model . .5. Heterotic construction (or, the S–dual story) . .6. Conclusion

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### The Geometry – Group Manifold

Consider agroup manifoldG (e.g. AdS3or S3)

There is a bi-invariant metric such that the isometry group is G× G The metric can be written in terms of the currents Jathat generate half of the symmetry

ds2[G] =

dim G

a=1

Ja⊗ Ja

If H⊂ G is compact, G is the total space of aHopf ﬁbrationover G/H:

H −−−−→ G

 y G/H Today H = U(1) and G/H = S2, AdS2.

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### The Geometry – Squashed group

SqG is a deformation of G described by thesame currents The symmetry group is G(R) × U(1) (only left-invariance)

The metric can be written in terms of the same Jacurrents. Fix dim G = 3 ds2[SqG] = J1⊗ J1+ J2⊗ J2+ 1

cosh2ΘwJ3⊗ J3 SqG is thebase space for a ﬁbrationthat has G× S1 total space

S1× S1 −−−−→ G × S1

 y G/U(1)

choose embedding

−−−−−−−−−−→

S1 −−−−→ G × S1

 y SqG the embedding of S1,→ S1× S1 is described by Θw

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### T-duality to “undo” ﬁbrations

ConstructNLSM on squashed groups via T-dualityfrom principal chiral models with group manifold target space G

We are not considering here conformal models: we start with the metric only (a B-ﬁeld will appear)

Main observation: if the space has a S1 ﬁbration structure S1 −−−−→ M

 y N

T-duality along the ﬁber will “undo” the ﬁbration and give adirect product M = Ne × S1

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### T-duality on the worldsheet

If there is a S1ﬁbration, the action can be written as S[ui, z] =

Σ

Gij(u) dui∧ ∗duj+(

dz + fi(u) dui)

∧ ∗(

dz + fj(u) duj) ,

which is to say, the metric has a block form ( Gij(u) + fi(u)fj(u) fi(u)

fi(u) 1

) .

we want to T-dualize the S1described by z.

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### T-duality on the worldsheet

introduce a gauge ﬁeld A and a Lagrange multiplier S[ui, A,ez] =

ΣGij(u) dui∧ ∗duj+(

A + fi(u) dui)

∧ ∗(

A + fi(u) dui)

− 2ezdA .

The EOM forez give

dA = 0 ⇒ A = dz , which leads back to the original action

The EOM for A gives

∗dez = A + fi(u) dui= dz + fi(u) dui.

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### T-duality on the worldsheet

The resulting action describes adirect product metricplus aB ﬁeld S[ui,ez] =

ΣGij(u) dui∧ ∗duj+ dez ∧ ∗dez − 2 dez ∧ fi(u) dui as promised

S1 −−−−→ M

 y N

−−−−→

T-duality

M = Ne × S1

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### Squashed groups

U(1) −−−−→ G × U(1)

 y SqG

the ﬁber is a linear combination of the U(1) and one direction in the Cartan of G

The metric on SqG is

ds2[SqG] = ds2[G] + tanh2Θ jC⊗ jC, whereΘ measures the combinationof the two U(1):

for Θ→ 0, SqG = G

for Θ→ ∞, SqG = G/U(1) × U(1).

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### Outline

. .1. Why are we here?

. .2. The main idea . .3. D–brane construction

. .4. Integrability of the Principal Chiral Model . .5. Heterotic construction (or, the S–dual story) . .6. Conclusion

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### Initial setup

Consider the superposition of aD1/D5system with amagnetic monopole and aplane wave

This is the T–dual of the D = 4 extremal dyonic black string.

The ﬁeld content is ds2= H1/21 H1/25

(

H−11 H−15 (

du dv + K du2 )

+ H−15 (

dy21+ . . . dy24 )

+ + V−1(

dψ + Aidxi)2

+ V (

dx21+ . . . dx23 ))

e= H−11 H5, F= H−11 dt∧ du ∧ dv − Bidxi∧ dψ where H1(x), H5(x), K(x), V(x), Ai(x), Bi(x) are harmonic functions of the transverse coordinates xi, i = 1, 2, 3 and

dB =− ∗ dH5, dA =− ∗ dV

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### Initial setup

Consider thenear–horizon limit ds2= QmQ1/21 Q1/25

(− dτ2+ dω2+ Qw2+ 2Qw1/2sinh ω dσ dτ )

+ QmQ1/21 Q1/25 (

2+ dφ2+ dψ2+ 2 cos θ dψ dφ )

+ Q1/21 Q−1/25 (

dy21+· · · + dy24) ,

F= QmQ1/21 Q1/25 (

cosh ω dτ∧ dω ∧ dσ + sin θ dφ ∧ dψ ∧ dθ) . The geometry isAdS3× S3× T4

The radii are ﬁxed by the monopole charge Qm(quantized) The plane wave charge appears in the AdS3part

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### Hopf–T–duality

We want to use the fact that

Single out a AdS3× S1 part from the ten-dimensional geometry ImplementHopf–T–duality.

If the geometry is the total space for a S1 ﬁbration and there are only Ramond–Ramond ﬁelds, theT–dual along the ﬁber has geometry B× S1.

S1 −−−−→ E

 y B

+ RR ﬁelds −−−→T–dual ( B× S1)

+ RR and NS ﬁelds

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### Hopf–T–duality

Starting from AdS3× S1: ds2= R2

(− dτ2+ dω2+ Qw2+ 2√

Qwsinh ω dσ dτ )

+

Q1 Q5dy21 F= R2cosh ω dτ∧ dω ∧ dσ

T–duality we obtain the metric we want: WAdS3× S1 ds2= R2

[

2− cosh2ω dτ2+ 1 cosh2Θw

(dβ + sinh ω dτ)2]

+ dζ2w

F4= R2

cosh2Θwcosh ω dω∧ dτ ∧ dβ ∧ dζw, F2= R tanh Θwcosh ω dω∧ dτ ,

H3= R tanh Θwcosh ω dω∧ dτ ∧ dζw.

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### Observations

Having started from a pure RR background, the geometry isglobally WAdS3. We can get orbifolds by adding NS ﬂuxes in the initial background Theparametersof the solution are understoodin terms of charges:

R2 = Qm

Q1Q5 sinh2Θw = 4QwQmQ5

the quantization of the deformation corresponds to the quantization of the linear combination of the ﬁbers.

The group SL2(R) has three different types of generators. Each can be chosen for this construction and lead to different geometries.

The same construction can be used to describe other squashed groups (simplest case: squashed S3)

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### Outline

. .1. Why are we here?

. .2. The main idea . .3. D–brane construction

. .4. Integrability of the Principal Chiral Model . .5. Heterotic construction (or, the S–dual story) . .6. Conclusion

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### Currents and EOM

Consider thePCM for a group G S =−1

2

ΣTr[dg(x, t)∧ ∗dg−1(x, t)] , where g is a map from the worldsheet to the group g : Σ→ G Theequations of motionare

d∗(g−1dg) = d∗(dg g−1) = 0 . these are the conservation laws for twocurrents

j = g−1dg , j =− dg g−1.

the currents areﬂatand thus fulﬁll the Maurer–Cartan (MC) equations:

dj + j∧ j = 0 , dj + j∧ j = 0 . Conservation and ﬂatness are the reasons for the integrability.

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### Lax current

We will consider only the left currents. The right side works in the same way Introduce theone-parameter familyof currents

J(x, t; ζ) =− ζ

1− ζ2(ζ j(x, t) +∗j(x, t)) where ζ∈ C is the spectral parameter.

The ﬂatness of J is an equation for the components (Jx, Jt), the so-calledLax equations:

tJx− ∂xJt+ [Jt, Jx] = 0 this is a Lax Pair.

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### Lax current

The ﬂatness of J and J implies both the EOM and the MC equations.

Conversely, imposing the EOM and MC equations results in the ﬂatness of the currents.

This can be easily veriﬁed by observing that dJ(ζ) + J(ζ)∧ J(ζ) = ζ

ζ2− 1(d∗j + ζ (dj + j ∧ j)) .

We started with a conserved current. Its ﬂatness implies theexistence of a one-parameter family of ﬂat currents.

Algebraically we passed from j∈ g to theloop algebraJ∈ g ⊗ C[ζ, ζ−1] We literally haveinﬁnitely more currents(after Fourier transform).

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### Wilson line

We have constructed inﬁnite currents. Where are theconserved charges?

Since J(ζ) is ﬂat we can introduce aWilson lineas the path-ordered exponential

W(x, t|x0, t0; ζ) = P {

exp [∫

C:(x0,t0)→(x,t)J(ξ, τ; ζ) ]}

,

and

J(x, t; ζ) = W−1(x, t; ζ) dW(x, t; ζ) . This generalizes the relation j = g−1dg to the loop algebra.

For spin chain experts: this is the transfer matrix.

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### Wilson loop and conserved charges

We can now deﬁne aone-parameter family of conserved charges:

Q(t; ζ) = W(∞, t| − ∞, t; ζ) = P {

exp [∫

−∞Jx(x, t; ζ) dx ]}

. note that Q goes “all around” the worldsheet. This is aWilson loop Key point: using theLax equationsand with appropriate BC, the one-parameter charge Q(t; ζ) is conserved

d

dtQ(t; ζ) = 0

Expand on ζ and ﬁnd aninﬁnite set of conserved charges Qn Q(t; ζ) = 1 +

n=0

ζn+1Q(n)(t) . for which

d

dtQ(n)(t) = 0, ∀ n = 0, 1, . . . .

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### Integrability of the PCM (in short)

The principal chiral model has twoconserved currentscorresponding to the G× G symmetryof the action

These currents are alsoﬂat

Out of these one can construct twoone-parameter families of ﬂat currents The Wilson loops of these currents are time-independent

The Fourier development givesinﬁnite conserved charges

These charges close under an inﬁnite-dimensional algebra (Yangianor afﬁne) the g⊕ g symmetry of the action is the zero mode of thebg ⊕ bgsymmetry of the equations of motion.

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### Integrability and squashed groups

How much of this structure remainsafter T–duality?

We have alinear transformation of the currentcomponents J(ζ)7→eJ(ζ) that leaves the (on-shell) ﬂatness conditions invariant:

deJ+eJ∧eJ= 0 ,

concretely we deﬁne T–dual Lax currents eJ(ζ) by imposing the condition

∗dez = dz + fi(u) dui.

Flatness is the key. This is preserved: the system isstill integrable.

The condition is not local (mix time and space derivatives). The resulting charges are all non-localanddo dot correspond to isometries.

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### A technical remark

The current that we use for T–duality does not commute with the others some of the components of J depend explicitly on z, when we have an equation for dz.

We need to perform agauge transformation J= h−1J h + h−1dh ,

after the transformation, the new current has a zero–mode (in the ζ expansion)

eJ(ζ) = h−1dh− Λ(ζ)h−1jh

dz=∗dez−fi(u) dui = eJ′(0)− Λ(ζ)ej.

for the experts: in the hierarchies we will have to covariantize w.r.t. eJ′(0).

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### The simplest example: Squashed three-sphere

eJ′1(ζ) =−ıΛ(ζ) sin θ dφ , eJ′2(ζ) =−ıΛ(ζ) dθ , eJ′3(ζ) =−ı

[

(1 + Λ(ζ))

(dα + cos θ dφ

cosh2Θ + tanh Θ∗dez )

− cos θ dφ ]

, eJ′4(ζ) =−ı tanh ΘΛ(ζ)(

∗dez − tanh Θ(

dα + cos θ dφ)) ,

and

eJ1(ζ) =−ıΛ(ζ)[ 1

cosh2Θcos φ sin θ dα− sin φ dθ + tanh2Θ cos φ sin θ cos θ dφ + tanh Θ cos φ sin θ∗dez] ,eJ2(ζ) = ıΛ(ζ)[ 1

cosh2Θsin φ sin θ dα + cos φ dθ− tanh2Θ sin φ sin θ cos θ dφ + tanh Θ sin φ sin θ∗dez] , eJ3(ζ) = ıΛ(ζ)

[ 1

cosh2Θcos θ dα +(

1− tanh2Θ cos2θ)

dφ + tanh Θ cos θ∗dez ]

, eJ4(ζ) = ı tanh ΘΛ(ζ)(

∗dez − tanh Θ(

dα + cos θ dφ)) .

we recoverSU(2)× SU(2) × U(1)currents even if the isometry is SU(2)× U(1) × U(1)

this is promoted to afﬁne when looking at thenon-local charges

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### Symmetries of the squashed group model

The action with squashed group target space is obtained via T–duality T–dualitypreserves the integrable structureof the PCM

Thefullbg ⊕ bgsymmetry is preserved

Onlypart of the zero-modes are realized as isometriesg⊕ u(1) The other zero modes are non-local

Adding RR ﬂuxesdoes not change the overall picture:

NS and R sectors are separated under T–duality We already know (from the previous section) the expressions for the RR ﬁelds

The PCM + RR ﬁelds is integrable and has an inﬁnite symmetry

This inﬁnite symmetry will be preserved

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### Outline

. .1. Why are we here?

. .2. The main idea . .3. D–brane construction

. .4. Integrability of the Principal Chiral Model . .5. Heterotic construction (or, the S–dual story) . .6. Conclusion

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### in Heterotic strings

AdS3is the target space for aWess-Zumino-Witten model The action can be written as

S[g] = k 16π

Σd2z⟨g−1∂g, g−1∂g¯ ⟩ + k 24π

M

⟨g−1dg, [g−1dg, g−1dg]⟩

where g∈ SL2(R), ∂M = Σ What is interesting for us is:

The model describes string propagating on AdS3target space ds2= k (J1⊗ J1+ J2⊗ J2+ J3⊗ J3)

The effective action at all orders in αis the classical action after a shift in k

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### Marginal deformations

WZW models admittruly marginal deformations(all orders in α).

The operator must have weight (1, 1). So it is written as a product of two currents

Oλ= λ

d2z

a,b

Ja(z)¯Jbz) .

The deformation S = SWZW+Oλ is truly marginal if the currents commute among each other

The resulting geometry preserves all the symmetries that commute with these currents.

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### as a marginal deformation

Remember the presence of an external U(1). Consider theWZW model for the group SL2(R) × U(1)

Oλ = λ

d2z J3(z)¯I(¯z)

where J3 is the hyperbolic left current in SL2(R) and¯Iis the right current in the U(1) component

The deformation is exact for all values of λ

The resulting geometry has symmetry U(1)× SL2(R) (the J3current used for the deformation and the right-moving initial SL2(R))

ds2= J1⊗ J1+ J2⊗ J2+ (

1− 2λ2) J3⊗ J3

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### Outline

. .1. Why are we here?

. .2. The main idea . .3. D–brane construction

. .4. Integrability of the Principal Chiral Model . .5. Heterotic construction (or, the S–dual story) . .6. Conclusion

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### Summary

Squashed group manifolds have met renewed attention during the last years Topologically massive gravity

Schrödinger spacetimes

They can be understood as natural deformations of group manifolds Using the Hopf ﬁbration structure we can constructtype II backgrounds.

Using the Lie algebra structure we can construct exactheterotic backgrounds.

Using both structures we can prove their classical integrability

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