REVIEW
D-Dbar mixing and new physics: general considerations and constraints on the MSSM
High Energy Physics - Phenomenology · Submitted 19 Mar 2007 · 24 references
Pith's verdict: A timely, careful letter that turns the 2007 D-mixing evidence into real bounds on up-type squark mixing — the flat A_SM prior is conservative, not fragile, so the δ limits hold up better than the reader thinks.
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Referee report
The paper
The paper claims
New D-meson mixing data turns into hard limits on the squark partners of the up and charm quarks, with aligned supersymmetry pushed toward the TeV scale.
The reading
What carries the argument
The argument runs on two machines. The first is a global fit that writes every charm mixing and CP observable in terms of just three quantities, $|M_{12}|$, $|Γ_{12}|$ and the phase $Φ_{12}$, so that the experimental inputs collapse onto a small parameter space; a flat prior on the Standard Model amplitude $A_{SM}$ over $[-0.02, 0.02]$ ps$^{-1}$ then converts the fitted $|M_{12}|$ into a probability distribution for the new-physics amplitude and phase. The second is the mass-insertion approximation in the super-CKM basis, where the off-diagonal squark mass terms $(δ^u_{12})_{AB}$ are treated as perturbations connecting up and charm squarks of helicity $A$ and $B$, divided by the average squark mass. Because the experimental bounds force these insertions to be small, the leading order of that expansion is an excellent approximation, and the translation from $A_{NP}$ to $(δ^u_{12})_{AB}$ is a one-loop calculation. Chirality-flipping insertions are punished by renormalization-group running, which is why the $LR$ and $LL=RR$ bounds come out an order of magnitude below the $LL$ one.
Extended reading notes
Core claim
The paper's central claim is that the newly reported $D-⁻D$ mixing evidence, combined with earlier charm measurements, is already sharp enough to constrain new physics in the up-quark sector. Fitting the world data on $x$, $y$, $|q/p|$, $y_{CP}$, $A_Γ$, $R_M$ and the strong phase $δ_{Kπ}$ simultaneously, the authors obtain $|M_{12}| = (7.7 ± 2.4) × 10^{-3}$ ps$^{-1}$ and $Φ_{12} = (2 ± 14)°$ (with a mirror solution near $180°$), and $|Γ_{12}| = (13.6 ± 3.5) × 10^{-3}$ ps$^{-1}$. Treating the full amplitude as a real Standard Model piece plus a new-physics piece $A_{NP} e^{iφ_{NP}}$, they find $A_{NP} < 0.006$ ps$^{-1}$ at 68% probability and $A_{NP} < 0.02$ ps$^{-1}$ at 95%, with $φ_{NP}$ restricted to bands near $0°$ and near $180°$. Feeding these into gluino-exchange box diagrams with next-to-leading-order Wilson coefficients and lattice $B$ parameters, they quote 95% bounds such as $|(δ^u_{12})_{LL}| < 0.033$ for $350$ GeV squarks and gluinos, tightening to $0.0020$ when left- and right-handed insertions are switched on together. These are roughly a factor of three stronger than the previous bounds in the literature.
Load-bearing premise
The Standard Model's own charm mixing amplitude is taken as a flat guess spread over $-0.02$ to $0.02$ ps$^{-1}$ rather than calculated, and that chosen range alone decides how much room is left for new physics and therefore sets every bound in the paper.
Editorial extensions
If this is right
- Any extension of the Standard Model that generates $D-⁻D$ mixing must keep its new-physics amplitude below about $0.006$ ps$^{-1}$ at 68% probability, with a CP-violating phase clustered near $0°$ or $180°$.
- In the Minimal Supersymmetric Standard Model with gluino mediation, the up-charm squark mixing entries obey 95% bounds of order $10^{-2}$ to $10^{-3}$ depending on helicity structure, for squark and gluino masses of a few hundred GeV.
- Supersymmetric models built on quark-squark alignment, which generically predict $(δ^u_{12})_{LL} \sim 0.2$, survive only if squark and gluino masses exceed roughly $2$ TeV.
- If the mixing amplitude turns out to be dominated by new physics, the measured phase $Φ_{12}$ becomes a direct experimental handle on the new-physics CP phase $φ_{NP}$.
Reading between the lines
- The charm sector has now joined the down-type sector as a place where flavour models can be checked, so alignment-type constructions face constraints from both up-type and down-type squarks at once; that squeeze is likely tighter than either bound applied separately.
- Because the quoted bounds scale roughly linearly with the assumed new-physics amplitude, a future lattice determination of the long-distance Standard Model charm mixing contribution would shift every number in the mass-insertion table, in either direction.
- The bound is quoted for gluino exchange only; extending the same fit to neutralino or chargino boxes, or to non-degenerate squark spectra, would test whether the factor-of-three improvement over earlier work survives when the mediator changes.
- The $2$ TeV conclusion is a statement about the simplest alignment ansatz; a model that aligns squarks only in the down sector, or that suppresses the up-charm entry by an additional flavour symmetry, would evade it without contradicting the data.
Original abstract
Combining the recently available experimental evidence of D-Dbar mixing, we extract model-independent information on the mixing amplitude and on its CP-violating phase. Using this information, we present new constraints on the flavour structure of up-type squark mass matrices in supersymmetric extensions of the Standard Model.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
Combining the recently available experimental evidence of D-Dbar mixing, we extract model-independent information on the mixing amplitude and on its CP-violating phase. Using this information, we present new constraints on the flavour structure of up-type squark mass matrices in supersymmetric extensions of the Standard Model.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Combining the recently available experimental evidence of D-Dbar mixing, we extract model-independent information on the mixing amplitude and on its CP-violating phase. | result 0.67 | 0.86 | 0.18 | asserted 1.00 |
| s1 | Using this information, we present new constraints on the flavour structure of up-type squark mass matrices in supersymmetric extensions of the Standard Model. | contribution 0.60 | 0.93 | 0.60 | asserted 0.99 |
What was examined, and what was not
- arXiv listing abstract v3
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
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- R cross-paper relations
Figures
Figures reproduced from arXiv:hep-ph/0703204 by the authors.
References
How the literature uses it
52 arXiv papers cite this in 76 sentences
Papers citing it · 46 sentences without a confident label
Uses its method or tool 2 papers
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This is performed using the formula ⟨D^0|ℋ_eff^ΔF=2|D^0⟩_i=∑_j=1^5 ∑_r=1^5 ( b_j^(r,i)+ηc_j^(r,i) ) η^a_j C_i(Λ) ⟨D^0|Q_r^cu|D^0⟩and the relevant inputs given in [ref] .
Lessons from Recent Measurements of D-\bar D Mixing · Model independent constraints · 0.84
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[ref] , in particular their eqs.
TeV Scale Left Right Symmetry and Flavor Changing Neutral Higgs Effects · Numerical Analysis · 0.99
Uses its data or values 11 papers
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In our calculation, the following inputs are adopted. $m_t=171.2$GeV, $M_W=80.4$GeV, $α_s(M_Z)=0.118$, and the mass [ref] , decay constants [ref] and the bag parameters [ref] are listed in Table.([ref]).
The Mass Difference of $F-\bar{F}$ with SO(3) Family Gauge Symmetry · Numerical results · 1.00
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Finally, concerning $D^0 -D̅^0$ mixing, we use as input the results for the NP amplitude obtained in Ref. [ref] combining the experimental information from Refs. [ref] .
Model-independent constraints on Delta F=2 operators and the scale of New Physics · Experimental input · 0.99
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The most stringent constraint in the up-sector comes from $ΔM_D$ [ref] : ΔM_D => |(δ^u_12)_LL|,|(δ^u_12)_RR| 6 ×10^-2 , |(δ^u_12)_LR|,|(δ^u_21)_LR| 10^-2 for $m_q̃ =0.5$ TeV.
Flavor Changing Neutral Higgs Bosons in a Supersymmetric Extension based on a $Q_6$ Family Symmetry · FCNC · 0.96
Compares with it 6 papers
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We obtain r/r_30.13, in agreement with previous works [ref] .
Flavor Changing Processes in Supersymmetric Models with Hybrid Gauge- and Gravity-Mediation · Holomorphic zeros · 0.89
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Using Eq. ([ref]) above, this results in the constraint on squark and gluino masses of (assuming $m_q̃ ≈m_g̃$ for simplicity) $m_g̃,q̃2$ TeV, which agrees with the results in Refs. [ref] .
Implications of D^0-\bar D^0 Mixing for New Physics · Quark-Squark Alignment Models · 0.94
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In this section we compare our bounds with those in the literature, derived from FCNC processes [ref] and vacuum stability (VS) bounds [ref] .
Supersymmetric renormalisation of the CKM matrix and new constraints on the squark mass matrices · Comparison with previous bounds · 1.00
Cites it as support 2 papers
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In particular, since $(δ^u_12)_LL$ and $(δ^d_12)_LL$ mass insertions are related to each other and the mass splitting between $d̃_L$ and $s̃_L$ by the Cabibbo angle, it appears less likely that squark and quark masses are merely aligned; rather a near degeneracy of at least the left-chiral squarks of the first two generations is necessary [ref] .
Supersymmetry beyond minimal flavour violation · $D - D̅$ mixing · 0.98
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Actually, by combining the constraints from $K^0-K^0$ mixing and $D^0-D^0$ mixing, one can show that this is the case independently of assumptions about the alignment [ref] .
Flavour Physics and CP Violation · The supersymmetric flavor puzzle · 0.98
Cites it as background 8 papers
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The highlight of this year's Moriond conference on electroweak interactions and unified theories arguably was the announcement by BaBar and Belle of experimental evidence for $D^0$-$D̅^0$ mixing [ref] , which was quickly followed by a number of theoretical analyses [ref] .
Implication of the D^0 Width Difference On CP-Violation in D^0-\bar D^0 Mixing · Introduction · 0.89
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Ref. [ref] has addressed $B$ mixing at NLO, Ref. [ref] contains an update of the constraints from $b→s$ transitions and Ref. [ref] has discussed D mixing.
Chirally enhanced corrections to FCNC processes in the generic MSSM · Introduction · 0.94
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It was discussed whether the measured size of the mixing parameters could be interpreted as a hint for physics beyond the standard model [ref] .
Brief Review of Charm Physics · Charm mixing · 0.88
Discussion
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