Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications

Transcription

1 Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications Joseph P. Conlon DAMTP, Cambridge University Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 1/4

2 This talk is based on hep-th/ (JC, D.Cremades, F. Quevedo) hep-th/ (JC, S. Abdussalam, F. Quevedo, K. Suruliz) hep-ph/061xxxx (JC, D. Cremades) and also uses results from hep-th/ (V. Balasubramanian, P. Berglund, JC, F. Quevedo) hep-th/ (JC, F. Quevedo, K. Suruliz) Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 2/4

3 Talk Structure Motivation Introduction and Review of Supersymmetry Breaking Computing Matter Metrics from Yukawa Couplings Results for Particular Models Applications: Soft Terms and Neutrino Masses Conclusions Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 3/4

4 Motivation! Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 4/4

5 Motivation The LHC! This will probe TeV-scale physics in unprecedented detail. If supersymmetry exists, it will (probably) be discovered at the LHC. Low-energy supersymmetry represents one of the best possibilities for connecting string theory (or any high-scale theory) to data. Understanding supersymmetry breaking and predicting the pattern of superpartners is one of the most important tasks of string phenomenology. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 5/4

6 MSSM Basics The MSSM is specified by its matter content (that of the supersymmetric Standard Model) plus soft breaking terms. These are Soft scalar masses, m 2 i φ2 i Gaugino masses, M a λ a λ a, Trilinear scalar A-terms, A αβγ φ α φ β φ γ B-terms, BH 1 H 2. The LHC will (hopefully) give experimental information about these soft breaking terms. Our task as theorists is to beat the experimentalists to the spectrum! Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 6/4

7 SUSY Breaking basics The soft terms are generated by the mechanism of supersymmetry breaking and how this is transmitted to the observable sector. Examples are Gravity mediation - hidden sector supersymmetry breaking Gauge mediation - visible sector supersymmetry breaking Anomaly mediaton - susy breaking through loop effects These all have characteristic features and scales. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 7/4

8 Gravity Mediation I In gravity-mediation, supersymmetry is Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 8/4

9 Gravity Mediation I In gravity-mediation, supersymmetry is broken in a hidden sector Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 8/4

10 Gravity Mediation I In gravity-mediation, supersymmetry is broken in a hidden sector communicated to the observable sector through non-renormalisable supergravity contact interactions Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 8/4

11 Gravity Mediation I In gravity-mediation, supersymmetry is broken in a hidden sector communicated to the observable sector through non-renormalisable supergravity contact interactions which are suppressed by M P. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 8/4

12 Gravity Mediation I In gravity-mediation, supersymmetry is broken in a hidden sector communicated to the observable sector through non-renormalisable supergravity contact interactions which are suppressed by M P. Naively, m susy F 2 M P This requires F GeV for TeV-scale soft terms. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 8/4

13 Gravity Mediation II The computation of soft terms starts by expanding the supergravity K and W in terms of the matter fields C α, W = Ŵ(Φ) + µ(φ)h 1H Y αβγ(φ)c α C β C γ +..., K = ˆK(Φ, Φ) + K α β(φ, Φ)C α C β + [ZH 1 H 2 + h.c.] +..., f a = f a (Φ). The function K α β(φ) is crucial in computing soft terms, as it determines the normalisation of the matter fields. Given this expansion, the computation of the physical soft terms is straightforward. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 9/4

14 Gravity Mediation III Soft scalar masses m 2 i j and trilinears A αβγ are given by m 2 α β = (m 2 3/2 + V 0) K α β F m F n ( m n Kα β ( m Kα γ ) K γδ ( n Kδ β) ) A αβγ = e ˆK/2 F m[ ˆKm Y αβγ + m Y αβγ ( ( m Kα ρ ) K ) ] ρδ Y δβγ + (α β) + (α γ). Any physical prediction for the soft terms requires a knowledge of K α β for chiral matter fields. However, K α β is non-holomorphic and thus hard to compute. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 10/4

15 What is known? In Calabi-Yau backgrounds, the Kähler metrics for (non-chiral) D3 and D7 position moduli and D7 Wilson line moduli have been computed by dimensional reduction. K D7 1 S + S K D3 1 T + T Using explicit string scattering computations, matter metrics for chiral D7/D7 matter have been computed in IIB toroidal backgrounds. K D7i D7 j 1 Tk + T k Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 11/4

16 This talk I will describe new techniques for computing the matter metric K α β for chiral matter fields on a Calabi-Yau. These techniques will apply to chiral D7/D7 matter in IIB compactifications. I will compute the modular dependence of the matter metrics from the modular dependence of the (physical) Yukawa couplings. I start by reviewing how Yukawa couplings arise in supergravity. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 12/4

17 Yukawa Couplings in Supergravity In supergravity, the Yukawa couplings arise from the Lagrangian terms (Wess & Bagger) L kin + L yukawa = K α µ C α µ Cᾱ + e ˆK/2 β γ W ψ β ψ γ = K α µ C α µ Cᾱ + e ˆK/2 Y αβγ C α ψ β ψ γ (This assumes diagonal matter metrics, but we can relax this) The matter fields are not canonically normalised. The physical Yukawa couplings are given by Y αβγ Ŷ αβγ = e ˆK/2 ( K α Kβ Kγ ) 1 2. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 13/4

18 Computing K α β (I) Y αβγ Ŷ αβγ = e ˆK/2 ( K α Kβ Kγ ) 1 2. We know the modular dependence of ˆK: ( ) ˆK = 2 ln(v) ln i Ω Ω ln(s + S) We compute the modular dependence of K α from the modular dependence of Ŷαβγ. We work in a power series expansion and determine the leading power λ, K α (T + T) λ k α (φ) + (T + T) λ 1 k α(φ) +... λ is the modular weight of the field T. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 14/4

19 Computing K α β (II) Y αβγ Ŷ αβγ = e ˆK/2 ( K α Kβ Kγ ) 1 2. We are unable to compute Y αβγ. If Y αβγ depends on a modulus T, knowledge of Ŷαβγ gives no information about the dependence K α β(t). Our results will be restricted to those moduli that do not appear in the superpotential. The main example will be the T -moduli (Kähler moduli) in IIB compactifications. In perturbation theory, Ti Y αβγ 0. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 15/4

20 Computing K α β (III) Y αβγ Ŷ αβγ = e ˆK/2 ( K α Kβ Kγ ) 1 2. We know ˆK(T). If we can compute Ŷαβγ(T), we can then deduce K α (T). Computing Ŷαβγ(T) is not as hard as it sounds! In IIB compactifications, this can be carried out through wavefunction overlap. We now describe the computation of Ŷαβγ for chiral matter on a stack of magnetised D7-branes. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 16/4

21 The brane geometry We consider a stack of (magnetised) branes all wrapping an identical cycle. If the branes are magnetised, chiral fermions can stretch between differently magnetised branes. This is a typical geometry in branes at singularities models. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 17/4

22 The brane geometry BULK BLOW UP Stack 1 Stack 2 Stack 3 Stack 4 Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 18/4

23 Computing Ŷαβγ We use a simple computational technique: Physical Yukawa couplings are determined by the triple overlap of normalised wavefunctions. These wavefunctions can be computed (in principle) by dimensional reduction of the brane action. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 19/4

24 Dimensional reduction Consider a stack of D7 branes wrapping a 4-cycle Σ in a Calabi-Yau X. The low-energy limit of the DBI action reduces to super Yang-Mills, S SY M = d n x g ( F µν F µν + λγ i (A i + i )λ ) M 4 Σ Magnetic flux on the brane gives chiral fermions ψ α in the low energy spectrum. These fermions come from dimensional reduction of the gaugino λ i. They are counted topologically by the number of solutions of the Dirac equation Γ i D i ψ = 0. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 20/4

25 Comments The full action to be reduced is the DBI action rather than that of Super Yang-Mills. In the limit of large cycle volume, magnetic fluxes are diluted in the cycle, and the DBI action reduces to that of super Yang-Mills. Our results will hold within this large cycle volume, dilute flux approximation. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 21/4

26 Computing the physical Yukawas Ŷαβγ Consider the higher-dimensional term L d n x g λγ i (A i + i )λ M 4 Σ Dimensional reduction of this gives the kinetic terms and the Yukawa couplings ψ ψ ψφψ The physical Yukawa couplings are set by the combination of the above! Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 22/4

27 Kinetic Terms L M 4 Σ d n x g λγ i (A i + i )λ Dimensional reduction gives λ = ψ 4 ψ 6, A i = φ 4 φ 6. and the reduced kinetic terms are ( ) Σ ψ 6 ψ 6 M 4 ψ4 Γ µ (A µ + µ )ψ 4 Canonically normalised kinetic terms require ψ 6 ψ 6 = 1. Σ Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 23/4

28 Yukawa Couplings L M 4 Σ d n x λγ i (A i + i )λ Dimensional reduction gives the four-dimensional interaction ( ) ψ 6 Γ I φ I,6 ψ 6 d M 4 xφ 4 ψ4 ψ 4. 4 Σ The physical Yukawa couplings are determined by the (normalised) overlap integral ( ) Ŷ αβγ = ψ 6 Γ I φ I,6 ψ 6. Σ Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 24/4

29 The Result Σ ψ 6 ψ 6 = 1, Ŷ αβγ = ( Σ ψ 6 Γ I φ I,6 ψ 6 ). For canonical kinetic terms, ψ 6 (y) 1 Vol(Σ), Γ I φ I,6 1 Vol(Σ), and so Ŷ αβγ Vol(Σ) 1 Vol(Σ) 1 Vol(Σ) 1 Vol(Σ) 1 Vol(Σ) This gives the scaling of Ŷαβγ(T). Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 25/4

30 Comments Q. Under the cycle rescaling, why should ψ(y) scale simply as ψ(y) ψ(y)? Re(T) A. The T -moduli do not appear in Y αβγ and do not see flavour. Any more complicated behaviour would alter the form of the triple overlap integral and Y αβγ - but this would require altering the complex structure moduli. The result for the scaling of Ŷαβγ holds in the classical limit of large cycle volume. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 26/4

31 Application: One-modulus KKLT We can now compute K α (T). In a 1-modulus KKLT model, all chiral matter is supported on D7 branes wrapping the single 4-cycle T. From above, Y αβγ Ŷ αβγ = e ˆK/2 ( K α Kβ Kγ ) T + T We know the moduli Kähler potential, ˆK = 3 ln(t + T) and so the matter Kähler potential must scale as K α (T + 1 T) 2/3. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 27/4

32 Application: Large-Volume Models BULK BLOW UP U(2) Q L e L U(3) U(1) Q R U(1) e R Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 28/4

33 Application: Large-Volume Models The overall volume is very large, V l 6 s, with small cycles τ s 10l 4 s. For the simplest model P 4 [1,1,1,6,9], the Kähler potential is ( ˆK = 2 ln V = 2 ln (T b + T b ) 3/2 (T s + T s ) 3/2). We can interpret the T s cycle as a local, blow-up cycle. We want K α (T) for chiral matter on branes wrapping this cycle. The gauge theory supported on a brane wrapping T s is determined by local geometry. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 29/4

34 Application: Large-Volume Models The physical Yukawa coupling Y αβγ Ŷ αβγ = e ˆK/2 ( K α Kβ Kγ ) 1 2 is local and thus independent of V. As ˆK = 2 ln V, we can deduce simply from locality that K α 1 V 2/3. As this is for a Calabi-Yau background, this is already non-trivial! Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 30/4

35 Application: Large-Volume Models We can go further. With all branes wrapping the same 4-cycle, Y αβγ Ŷ αβγ = e ˆK/2 ( K α Kβ Kγ ) τs. We can then deduce that K α τ1/3 s V 2/3. We also have the dependence on τ s! Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 31/4

36 Application: Large-Volume Models The dependence K α 1 V 2/3 follows purely from the requirement that physical Yukawa couplings are local. The dependence on τ s, K α τ1/3 s V 2/3 follows from the specific brane configuration (all D7 branes wrapping the same small cycle). Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 32/4

37 Application: Large-Volume Models If we wrap branes on the large cycle, as for the one-modulus KKLT model we find K 1 (T b + T b ) 2/3. All the above results hold for both diagonal and non-diagonal matter metrics. The reason is that the T moduli do not see flavour, and so the T -dependence is flavour-universal. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 33/4

38 Soft Terms We can use the above matter metric to compute the soft terms for the large-volume models. We get M i = F s 2τ s M, m α β = M 3 Kα β, A αβγ = M Ŷαβγ, B = 4M 3. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 34/4

39 Soft Terms These soft terms are the same as in the dilaton-dominated heterotic scenario. They are also flavour-universal. This is surprising - there is a naive expectation that gravity mediation will give non-universal soft terms. Why? Flavour physics is Planck-scale physics, and in gravity mediation supersymmetry breaking is also Planck-scale physics. Naively, we expect the susy-breaking sector to see flavour and thus give non-universal soft terms. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 35/4

40 Soft Terms: Flavour Universality These expectations are EFT expectations In string theory, we have Kähler (T ) and complex structure (U) moduli. These are decoupled at leading order. ( ) K = 2 ln (V(T)) ln i Ω Ω(U) ln(s + S). Here, U sources flavour and T breaks supersymmetry. At leading order, susy-breaking and flavour decouple. The origin of universality is the decoupling of Kähler and complex structure moduli. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 36/4

41 Soft Terms: Phenomenology We run the soft terms to low energy using SoftSUSY and study the spectrum. The constraints are given by tan β GeV 3.2x x10-4 δµ b->sγ m h Ω h 2 LSP type allowed A B 1.8x M/GeV Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 37/4

42 Neutrino Masses The theoretical origin of neutrino masses is a mystery. Experimentally 0.05eV m H ν 0.3eV. This corresponds to a Majorana mass scale M νr GeV. Equivalently, this is the suppression scale Λ of the dimension five Standard Model operator O = 1 Λ HHLL. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 38/4

43 Neutrino Masses In the supergravity MSSM, consider the superpotential operator λ M P H 2 H 2 LL W, where λ is dimensionless. This corresponds to the physical coupling e ˆK/2 λ M P H 2 H 2 LL ( K H2 KH2 KL KL ) 1 2. Once the Higgs receives a vev, this generates neutrino masses. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 39/4

44 Neutrino Masses Using the large-volume result K α τ1/3 s, this becomes V 2/3 λv 1/3 τs 2/3 H 2 H 2 LL. M P Use V (to get m 3/2 1TeV) and τ s 10: λ GeV H 2H 2 LL With H 2 = v 2 = 174GeV, this gives m ν = λ(0.3 ev). Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 40/4

45 Large Volumes are Powerful In large-volume models, an exponentially large volume appears naturally (V e c gs ). A volume V l 6 s, required for TeV-scale supersymmetry, automatically gives the correct scale for neutrino masses. This same volume also gives an axion decay constant in the allowed window (JC, hep-th/ ), 10 9 GeV f a GeV. This yoking of three distinct scales is very attractive. The origin of all three hierarchies is the exponentially large volume. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 41/4

46 Conclusions Kähler metrics for chiral matter enter crucially in the computation of MSSM soft terms. I have described techniques to compute these in IIB Calabi-Yau string compactifications. We computed the modular weights both for one-modulus KKLT models and for the multi-modulus large-volume models. The soft terms are flavour-universal, which comes from the decoupling of Kähler and complex structure moduli. For the large-volume models, TeV-scale supersymmetry naturally gives the correct scale for neutrino masses. Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 42/4

47 Kähler Potentials for Chiral Matter in Calabi-Yau String Compactifications p. 43/4