dynamical fermion simulations: a critical status report · wilson plaquette gauge action and wilson...
TRANSCRIPT
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Dynamical Fermion Simulations:
A Critical Status Report
Karl Jansen
• Lattice actions(an over-critical account)
• Performance comparison
• Systematics
continuum limit scaling nite size eects chiral perturbation theory renormalization eects of strange quark mixed action
• Conclusion
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Welcome to the lattice and its dangerous animals
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Bem-vindos `a rede e seus animals perigososÄîáðî ïîæàëîâàòü â òåîðèþ êàëèáðîâî÷íûõ ïîëåé íà ðåø¼òêàõ... Èâ ìèð å¼ îïàñíûõ æèâîòíûõ!
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Bienvenidos a la Red y sus peligrosos animales
Dobrodosli na resetku i opasne zivotinje na njoj
Willkommen auf dem Gitter und seinen gefährlichen Tieren
Witajcie na sieci, gdzie »yj¡ niebezpieczne zwierz¦ta
Kal¸c rjate sto plègma kai ta gria jhrÐa tou
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0.15
0.10
0.05
0.001.0
0.8
0.6
0.4
0.2
0.0
600500
400300
200100
mπL = 3.5
exptJLQCD(2001) Nf = 2
MILC Nf = 2 + 1
RBC-UKQCD Nf = 2 + 1
PACS-CS Nf = 2 + 1
JLQCD Nf = 2 + 1
JLQCD Nf = 2
CLS Nf = 2
CERN-ToV Nf = 2
QCDSF Nf = 2
ETMC Nf = 2
a [fm]
1/L [fm−1]mπ [MeV]
a[fm]
1/L [fm−1]
0.15
0.10
0.05
0.001.00.80.60.40.20.0
a[fm]
mπ [MeV]
0.15
0.10
0.05
0.00600500400300200100
1/L [fm−1]
mπ [MeV]
1.0
0.8
0.6
0.4
0.2
0.0600500400300200100
The parameter landscape (thanks to G. Herdoiza)
a[fm]
1/L[fm−1]MPS[MeV]
a[fm] a[fm] 1/L[fm−1]
1/L[fm−1] MPS[MeV] MPS[MeV]
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Non-perturbatively improved Wilson Fermions
This is most probably the best formulation of lattice QCD!
DRAWBACK
• for full non-perturbative O(a)-improvement
→ nonperturbative operator improvement neccessary→ very demanding (e.g. PDFs, formfactors etc.)→ sometimes neglected
• mixing under renormalization
• Moderate smearing can be helpfuldoes it harm?
• No infrared regulating quark mass
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Non-perturbatively improved Wilson Fermions
• No infrared regulating quark mass
however
stability through
spectral gap
(CERN)
0 10 20 30 40 50 60 70
|λ| [MeV]
mPS=360 MeV mPS=520 MeV
mq=28 MeV mq=58 MeV
smallest eigenvalue distribution with median µ and width σ
A1 A2 A3 A4 B1 B2 C1 D10.4
0.6
0.8
1
1.2
1.4
1.6
1.8
σ√ V /a median of distribution µ ≈ Zm
demanding µ ≥ 3σ
→ m ≥ 3a/Z√
V
→ mπL ≥√
3√
2aB/Z
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Stability and Meta-Stability(C. Urbach, K.J.)
Wilson plaquette gauge action and Wilson fermion action
β L mPSL µ σ
5.2 16 8 0.0103 0.0013
5.3 16 4 0.0038 0.0010
hot start
mPSL > 8
µ
ρ
0.0140.0120.010.0080.0060.0040.0020
400
350
300
250
200
150
100
50
0
⇒ all criteria fulllled
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Stability and Meta-Stability
cold
hot
tHMC
〈P 〉
180016001400120010008006004002000
0.55
0.54
0.53
0.52
0.51
0.5
0.49
cold
hot
tHMC
〈P 〉
120010008006004002000
0.56
0.555
0.55
0.545
0.54
0.535
0.53
0.525
0.52
→ dierent (hot and cold) starts
→ long-living metastable states at β = 5.2 and β = 5.3
→ check for metastable behaviour towards the chiral limit(Sharpe, Wu; Münster, Hofmann; Scorzato; Farchioni et.al.)
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rooted staggered fermions
This is most probably the best formulation of lattice QCD!
DRAWBACK
• rooting issue still being discussed
non-local at a > 0 ⇒ scaling law towards continuum limit? theoretical analysis (Shamir; Sharpe; Bernard, Golterman, Shamir, Sharpe; Adams) non-perturbative couplings of tastes (Creutz)
• usage of non-exact RHMD algorithm
used for large volume simulations no eect on plaquette (Toussaint) dierence: O(10−7)
(is it safe? what about e.g. correlators?) exact RHMC algorithm about factor of 2 more expensive (Gottlieb, Toussaint)
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rooted staggered fermions: two points of view
view I
• First continuum limit, then chiral limit• needs minimal pion mass
continuum ChPT: taste splitting M2PS
staggered ChPT: taste splitting . M2PS
a = 0.060fm: M2PS = (≈ 220MeV)2 ≈ 3∗ taste splitting
a = 0.125fm: M2PS = (≈ 250MeV)2 ≈ taste splitting
• Symanzik-like analysis (Bernard, Golterman, Shamir)
Dtaste = Dinv + ∆ bound: ‖D−1inv∆‖ . a/( ma2
c︸︷︷︸blocked
)
⇒ continuum limit rst
• Order of limits: studied in Schwingermodel:(Dürr, Hoelbling)
strategy seems to be working for all practical purposes→ visit MILC presentations
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rooted staggered fermions: two points of view
view II
• Explore the chiral limit at xed lattice spacingin the end we are theorists ...
• check 't Hooft vertex (Creutz)(more general: observables related to instanton physics)
• explore ε-regime with simulations and chiral perturbation theory
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maximally twisted mass fermions
This is most probably the best formulation of lattice QCD!
DRAWBACK
L = 2.8 fm mπ ∼ 300 MeVL = 2.2 fm mπ ∼ 300 MeV
mπ ∼ 450 MeV
r20((m
±
PS)2 − (m0
PS)2)
(a/r0)2
0.040.030.020.010.00
0.4
0.3
0.2
0.1
0.0
r0fPS = 0.400r0fPS = 0.375r0fPS = 0.345
r0mPS
(a/r0)2
0.060.040.020
1.30
1.20
1.10
1.00
0.90
0.80
0.70
0.60
0.50
• neutral pion becomes zero at µtm = µcrittm
• isospin breaking
observation I
charged minus neutral only charged
→ large cuto eects in neutral pion mass
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maximally twisted mass fermions
Observation II
RO = O±−O0
O±
β aµq RO
afPS 3.90 0.004 0.04(06)4.05 0.003 −0.03(06)
amV 3.90 0.004 0.02(07)4.05 0.003 −0.10(11)
afV 3.90 0.004 −0.07(18)4.05 0.003 −0.31(29)
am∆ 3.90 0.004 0.022(29)4.05 0.003 −0.004(45)
• Isospin splittingscompatible with zerofor other (so far)considered observables
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maximally twisted mass fermions
interpretation
analysis a la Symanzik
(m0PS)
2 = m2π + a2ζ2
π +O(a2m2π, a4) , ζπ ≡ 〈π0|L6|π0〉|cont
(m±PS)
2 = m2π +O(a2m2
π, a4)
ζπ has a large contribution:
ζ2π/Λ4
QCD ∼ 25 a2Λ4QCD
size of isospin violation needs case by case study
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high (6) level stout smeared Wilson Fermions
This is most probably the best formulation of lattice QCD!
DRAWBACK
• alter short distance behaviour?
→ here: look at static action (Farchioni,Montvay, Urbach, Wagner, K.J.)
0
0.5
1
1.5
2
0 2 4 6 8 10
Ve
ffe
ctiv
e a
T / a
effective masses for R / a = 6 for different static actions
no smearing1 HYP2 smearing step6 stout smearing steps
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10
(V -
V0)
a
R / a
static potentials for different static actions
6 stout smearing steps1 HYP2 smearing step
no smearing
Veff from below no change at R/a relevant for r0
shift r0 ≈ 6.0→ r0 ≈ 4.8 why smaller?
→ compare lattice spacing from fermionic observable → in progress
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high (6) level stout smeared Wilson Fermions
• alter short distance behaviour?
→ check localization range of gauge eld interaction
0 1 2 3 4 5 6 7
|z|/a
10-6
10-5
10-4
10-3
10-2
10-1
100
||¶D(x
,y)/¶Um(x
+z)
||
a~~0.125 fma~~0.085 fma~~0.065 fm
(BMW collaboration)
→ nd exponential localization
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Domain wall Fermions
This is most probably the best formulation of lattice QCD!
DRAWBACK
• Domain Wall Fermions with NS <∞ break chiral symmetry(as do imprecisely approximated overlap fermions)
← studied by RBC-UKQCD collaboration
• cost of improved chiral symmetry? → later
• comparison mres and mminsea
a−1 mminsea mmin
val mres
1.73 0.005 0.001 0.00315(2)
2.42 0.004 0.002 0.000665(13)
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Domain wall Fermions
• Changing topology
1.9 2 2.1 2.2 2.3 2.4
β
0.0001
0.001
0.01
0.1
mre
s (L
s=3
2)
• eigenvalue density of kernel operator
ρ(0)→ 0 for β →∞
mres ∝ ρ(0)/Ls
⇒ topology change forbidden for a→ 0
• consequence of negative quark massplaquette bound
• holds true also for overlap fermions
mres(Ls) Ls xed
β
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Changing topology
what about other fermions?
Schwinger model with Wilson fermions (Christian, K.J.)
-1
0
1
0 100 200 300 400 500
Monte-Carlo Time
Topolo
gic
alC
harge
β = 5
-1
0
1β = 6
-1
0
1β = 10
diculty to change topology in principle problem for everybody→ think about algorithms
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overlap fermions
This is most probably the best formulation of lattice QCD!
Nigel Cundy Topology with dynamical overlap fermions
Summary
• Dynamical overlap fermions are difficult
• Correctly sampling topological sectors with dynamical overlapfermions is even more difficult
• But it is possible
• And with luck, I will have some physics to share some time inthe next century
Trento, May 2008 29/29
• However, there are simulations: 83 · 16see also (DeGrand, Schäfer)
• what about the Mandula concern?
2.5
3
3.5
4
4.5
5
5.5
6
0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.055χ
t
mq
χtop
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overlap fermions in xed topology
This is most probably the best formulation of lattice QCD!
• eects of xing topology topological nite size eects (Brower et.al., Aoki et.al) algorithmic ergodocity loss of clustering properties• worth the eort? → main motivation: ε-regime
xed point action(P. Hasenfratz, Hierl, Maillart, Niedermayer, A. Schäfer, Weiermann, Weingart)
Wilson action (A. Hasenfratz, Homan, S. Schäfer) twisted mass action (Nube, Shindler, Urbach, Wenger, K.J.)
⇐ formulae in ChPT available summing over all topologies
• Wilson determinant and O(a) eects?
• τint,Ninv∝ O(100); Q independent?
• continuum form of chiral Lagrangian butbreaking of Lorentz invariance
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Other Collaborations/Fermions
These are for sure ...
• Flic fermions (CSSM)
• Chirally improved fermions (BGR collaboration)
• Fixed point action (Bern group)
• Stout smeared Wilson (Hasenfratz, Homann, Schäfer)
Disclaimer: Don't forget, I have been over-critical here and played devil's advocate!
In general, I think, we are doing very well
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Cost of simulations
cost formula
Cop = k(20 MeV
m
)cm (L
3 fm
)cL(0.1 fm
a
)ca Tflops× years
m renormalized quark mass at 2GeV
(sorry for shoehorning you to this form ...)
action k cm cL ca
Wilson 0.3 1 5 6(DDHMC)
staggered 0.016 1 4 4(RHMC)
tmQCD 0.8− 2.1 2 5 6(MTMHMC)
k, ca, cm, cL : large uncertainties
not to be taken as denite
e.g. ca not conrmed by ETMC data(scaling in a much weaker)
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Updated Berlin Wall plot
L = 2.1fm a = 0.087fm, MPSL = 3.51000 independent congurations
tremenduous algorithmic improvementfolded with machine capacities outperforming Moore's law⇒ realistic simulations
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It's universality
Example of the Schwinger model(N. Christian, K. Nagai, B. Pollakowski, K.J.)
OverlapHypercube
1
β
mπ
√
β
0.88
0.86
0.84
0.82
0.80
0.78
0.76
0.74
10.80.60.40.20
Twisted massWilson
1
β
mπ
√
β
1 0.8 0.6 0.4 0.2 0
0.88
0.86
0.84
0.82
0.80
0.78
0.76
0.74
• mquark
√β xed
• observe a2 scaling
• universality of continuum limit
• ≈ 10% scaling violation
= a2
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Continuum limit scaling(Urbach, K.J.)
• use r0 but consider r0 as scaling variable not as physical quantity
• r0 better than using the scale a−1
• r0 extrapolated to the physical point
• x r0MPS = 0.8, 1.0, 1.2
• consider r0fPS and r0Mnucleon
• nite size corrections are taken into account (fPS,MPS)
note: fPS does not need renormalization for overlap, twisted mass and staggered fermions
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Continuum limit scaling: nucleon mass
LHP nf = 2 + 1PACS-CS nf = 2 + 1
JLQCD nf = 2QCDSF-UKQCD nf = 2
RBC-UKQCD nf = 2 + 1MILC, nf = 2 + 1
ETMC, nf = 2
(r0mPS)2
r0m
N
43.532.521.510.50
4.5
4
3.5
3
2.5
2
1.5
• the nucleon mass revisited
only smallest lattice spacing
→ no obvious discrepancy
→ eects of scale setting
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LHPC nf = 2 + 1 mixedJLQCD nf = 2
RBC-UKQCD nf = 2 + 1MILC nf = 2 + 1
ETMC nf = 2
r0mPS = 1.2
r0mPS = 1.0
r0mPS = 0.8
(a/r0)2
r 0m
N
0.120.10.080.060.040.020
3.4
3.2
3
2.8
2.6
2.4
2.2
2
QCDSF nf = 2PACS-CS nf = 2 + 1
ETMC nf = 2
r0mPS = 1.2
r0mPS = 1.0
r0mPS = 0.8
(a/r0)2
r 0m
N
0.120.10.080.060.040.020
3.4
3.2
3
2.8
2.6
2.4
2.2
2
Continuum limit scaling: nucleon mass
staggered, DW, overlap Wilson fermions only
→ nd overall consistency
→ eventually combined continuum limit possible
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Continuum limit scaling: fPS
JLQCD nf = 2CERN nf = 2
QCDSF-UKQCD nf = 2RBC-UKQCD nf = 2 + 1
MILC, nf = 2 + 1ETMC, nf = 2
data not FS corrected!
(r0mPS)2
r 0f P
S
32.521.510.50
0.5
0.45
0.4
0.35
0.3
0.25
0.2
smallest lattice spacing only
no signs of common scaling
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Continuum limit scaling: fPS
JLQCD nf = 2CERN nf = 2
QCDSF-UKQCD nf = 2RBC-UKQCD nf = 2 + 1
MILC, nf = 2 + 1ETMC, nf = 2
data not FS corrected!
(mPS/mPS,ref)2
f PS/f
PS,r
ef
32.521.510.50
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6JLQCD nf = 2
MILC nf = 2 + 1ETMC nf = 2
r0mPS = 1.2
r0mPS = 1.0
r0mPS = 0.8
(a/r0)2
r 0f P
S
0.120.10.080.060.040.020
0.45
0.4
0.35
0.3
0.25
FPS normalized to reference point only formulations with ZA = 1
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Continuum limit scaling: fPS
possible sources of mismatch
• non-perturbative renormalization factor ZA
• value for r0
varies from r0 = 0.45− 0.5fmvaries in time ...
• nite size eects
• Nf versus Nf = 2 + 1
⇒ need to understand this!
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Do we need non-perturbative renormalization?
• strange quark mass (tm-example, arXiv:0709.4574)
ZRI−MOMP (1/a) = 0.39(1)(2) ← non-perturbative RI-MOM method
ZBPTP (1/a) ' 0.57(5) ← one-loop boosted perturbation theory
mMSq (2GeV)MeV perturbative non-perturbative
mud 2.63± 0.08± 0.36 3.85± 0.12± 0.4mud (PACS-CS) 2.53± 0.05
ms 72± 2± 9 105± 3± 9ms (PACS-CS) 72.7± 0.8
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Do we need non-perturbative renormalization?
• want massless renormalization scheme
Nf = 2RI-MOM: chiral extrapolationSF: direct at mquark = 0
Nf = 2 + 1RI-MOM: presently, only light quarks chirally extrapolated, strange xed(RBC-UKQCD) estimates systematic eectsSF: rst simulations (talk by Taniguchi)
• renormalization needs dedicated runs with Nf = 3 mass degenerate quarks
• appetizer: this checks simultaneously SU(3) ChPTMILC is planning to perform such runs
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Eects of dynamical strange?
strange quark mass compilation (compiled by V. Lubicz)
40 60 80 100 120 140 160 180 200ms (2 GeV) [MeV]
CP-PACS 01
JLQCD 02
ALPHA 05
SPQcdR 05
QCDSF-UKQCD 04-06
ETMC 07
HPQCD-MILC-UKQCD 04-07
CP-PACS-JLQCD 07
PDG 06 Average
(W-Clov, a-->0, PT)
(W-Clov, a=0.09 fm, PT)
(W-Clov, a=0.07 fm, SF)
(Wilson, a=0.06 fm, RI-MOM)
(W-Clov, a-->0, RI-MOM)
(TM, a=0.09 fm, RI-MOM)
(KS, a-->0, PT)
(W-Clov, a-->0, PT)
(Lattice only)
RBC 07(DWF, a=0.12 fm, RI-MOM)
(DWF, a=0.11 fm, RI-MOM)RBC-UKQCD 08
PACS-CS 07(W-Clov, a=0.09, PT)
Nf=2
Nf=2+1
→ no obvious eect of dynamical strange quark
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MILCETMC
(a/r0)2
r0m
Ω
0.080.060.040.020
5
4.8
4.6
4.4
4.2
4
3.8
3.6
Eects of dynamical strange?
take the Ω(sss− baryon)-mass: chiral limit, no strong decay
• r0MPS xed
→ no obvious eect (however, large errors)
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Mixed action
overlap on twisted mass sea: match MPS (Garron, Scorzato)
→ nd at matching point: fPS(tm) = 0.0646(4)
fPS(overlap) = 0.054(3)
domain wall on rooted staggered fermions: match MPS (LHP collaboration)
→ nd at matching point: Mnucleon(staggered) = 0.723(6)
Mnucleon(domainwall) = 0.696(7)
check cuto eects in mixed action calculations
→ chiral perturbation theory analysis(Bär, Rupak, Shoresh; Golterman, Izubuchi, Shamir)
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where to apply 1-loop and 2-loop chiral perturbation theory?
• SU(2) χPT
β = 4.05
β = 3.90
NNLO χPT
NLO χPT
r0µRr 0
fP
S
0.20.150.10.050
0.45
0.40
0.35
0.30
0.25
(JLQCD) (ETMC)
x = 2B0mq
(4πf)2x = 2B0mq
(4πf)2
x = ( mπ4πf )2 nite size corrected
ξ = ( mπ4πfπ
)2 ⇒ NLO for MPS . 450MeV valid (?)
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NNLO needed?
scalar radius:
log in
log may
become signiÞcant beyond the region of lattice data.
← JLQCD
〈r2〉πV = 1(4πfπ)2
[ln m2
πµ2 + 12(4π2)l9
]also seen byETMC
〈r2〉πcharge = 1(4πfπ)2
[ln Λ2
62Bm − 1
]
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Nf = 2 + 1 avours
• SU(3) chiral perturbation theoryexample: (PACS-CS)
0 0.01 0.02 0.03
mud
AWI
0.05
0.06
0.07
0.08
0.09
0.10
κs=0.13640
κs=0.13660
chptchpt@ph
fπ
0 0.01 0.02 0.03
mud
AWI
0.06
0.07
0.08
0.09
0.10
κs=0.13640
κs=0.13660
chptchpt@ph
fK
⇒ SU(3) not a good descriptionalso concluded by other groups
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Nf = 2 + 1 avours
• SU(2) chiral perturbation theory partially quenched chiral perturbation theory ts work for mquark . 0.01 (MPS . 450 MeV)
(0.06 fm) results are to the continuum extrapolation.
0.08
0.09
0.1
0.11
0 0.01 0.02 0.03 0.04mx
my = 0.04fit: mx ≤ 0.01
fxy
ml=0.005ml=0.01
mx=mlmx=ml=mud
(MILC) (RBC-UKQCD)
rooted staggered perturbation theory kaon ChPTadd NNLO anayltic terms issue of uncorrelated ts(only sea quark data shown)
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Nf = 2 + 1 avours
staggered data at a = 0.06fm seem to be close to continuum ⇒
• SU(2) 2-loop continuum chiral perturbation theory(rSχPT is not catching up to this order)
→ extend t range
(C. Bernard, MILC)
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A comparison
B f l3 l4
SU(2)×SU(2) 2.414(61) 0.0665(21) 3.13(33) 4.43(14)
SU(3)×SU(3) 2.457(78) 0.0661(18) 2.87(28) 4.10(05)
MILC (Nf = 2 + 1) 0.6(1.2) 3.9(5)
MILC, pure NLO 2.85(07) –
ETMC (Nf = 2) 3.44(08)(35) 4.61(04)(11)
CERN (Nf = 2) 3.0(5) –
phenom. 2.9(2.4) 4.4(0.2)
E. Scholz, RBC-UKQCD
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Summary chiral perturbation theory
Nf = 2
• SU(2) χPT seems to work for MPS . 450MeV
2-loop eects seem to be important for pion radii constraining ts, add more observables,
go down to 200MeVpion masses
Nf = 2 + 1
• SU(3) χPT not working for kaon sector
to explore SU(3) χPT → need Nf = 3 simulations(seems to be request from χPTheorists (Colangelo) )
SU(2) χPT including lattice artefacts works for MPS . 450MeV continuum SU(2) χPT at NNLO
nal check: χPT after continuum extrapolation
understand scaling
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Topological susceptibility
→ χtopo shows right behaviour in chiral limit
→ χtopo particularly important for xed topology
(RBC-UKQCD) (MILC)
0 0.05 0.1 0.15 0.2 0.25r0 (m
u + m
res)
0
0.01
0.02
0.03
0.04
0.05
Topolo
gic
al susceptibili
ty, r 0
4χ
16332, L
s=16
24364, L
s=16
Iwasaki gauge action, a~0.13 fm
Curve is based on measured and 43
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η2 mass
• η2 (Nf = 2) analogue of η′ (Nf = 2 + 1)
DWF r0/a = 4.28CP-PACS r0/a = 4.49UKQCD r0/a = 5.04UKQCD r0/a = 5.32
ETMC r0/a = 6.61ETMC r0/a = 5.22 L = 32ETMC r0/a = 5.22 L = 24
(r0mπ)2
r 0m
η
3210
3
2
1
0
(ETMC)
→ reach small pion masses
→ conrm mass of η2 ≈ 700MeV
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Finite size eects
Comparison of data at several volumes to :
rSχPT CDH (Colangelo, Dürr, Haefeli)
observed “boosted” 1-loop rS PTquantity
1.4(2)% 1.6(2)% 1.1%0.4(3) % 0.4(3) % 0.3%
% % %% % %
observ. MPSL meas. [%] CDH [%]MPS 3.0 +6.2 +6.1fPS 3.0 −10.7 −10.3MPS 3.5 +1.1 +1.5fPS 3.5 −1.8 −2.9
(MILC) (ETMC)
MPSL = 4 relative deviation: RO = OL−O∞)O∞
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Finite size eects from SU(3) ChPT
50 100 150 200 250 300 350 400mπ [MeV]
0.00
0.02
0.04
0.06
0.08
0.10
X=mπX=mKX=fπ
X=fK
|RX|• RX = (X(L)−X(∞))/X(∞)
• L = 3fm
(PACS-CS)
→ nite size eects small even at physical point
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Dangerous nite size eects
FS corrected Corrections gA/gV in DWF
0 0.1 0.2 0.3 0.4 0.5mπ
2[GeV2]
0.7
0.8
0.9
1
1.1
1.2
1.3
Nf=2+1(2.7fm)Nf=2+1(1.8fm)Nf=2(1.9fm)experiment
gA/gV(DWF)
(QCDSF) (RBC-UKCD)
predict: L = 2.5fm, MPS = 140MeV: 20%
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Some bounds for simulations
stability bound δ expansion
mπL ≥√
3√
2aB/Z
nite size eects minimal pion mass
MPSL ≥ 3.5 MPSL ≥ 3/2∗f20L2
1.+5.7/4∗π∗f20L2
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Getting social
• ILDG: put congurations on the net! (talk by T. Yoshie)
• Codes: publish code (MILC (arXiv:0806.2312), Lüscher, Borici)
• Techniques: publish papers with all technical details
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Challenges for dynamical simulations
• Decay of unstable particles, resonances
• Disconnected contributions
• Change of topological charge towards the continuum limit
• Blind test of data analysis
• Collaborations with non-lattice peoplee.g.: (Allison et.al., arXiv:0805.2999)
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Conclusion: there is a rooting problem!
Who do we root for now?Which dynasty do we want continuing to wave its victorious ag?
• thanks to algorithmic, machine and conceptual improvements:→ after many years of preparatory work simulations are done at
Pion mass: 200MeV . MPS and even MPS = 140MeV lattice spacing: 0.05fm . a lattice size: MPS · L ≥ 3.5
• investigate more: systematics of dierent lattice formulations:fourth root, stouting, isopin breaking, autocorrelations,residual mass, topology xing, ...
• observations: scaling towards continuum limit problematic, e.g. fPS
applicability of χPT up to the strange quark questionable need massless renormalization with dynamical strange quark dangerous nite size eects, e.g. gA
mixed action may have non-negligible cuto eects
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Conclusion: whom to root for?
• the dynasties:BMW, CLS, PACS-CS, ETMC, JLQCD, MILC, QCDSF, PACS-CS, RBC-UKQCDLet's go for all ⇒ universality will tell
0
500
1000
1500
2000
M[MeV]
p
K
r K*NLSX D
S*X*O
experiment
width
QCD
(BMW collaboration)
52