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Constraints on charged Higgs bosons from D(s)+- -> mu+- nu and D(s)+- -> tau+- nu

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A.G. Akeroyd, F. Mahmoudi

High Energy Physics - Phenomenology · Submitted 16 Feb 2009 · 75 references

Pith's verdict: A careful, modest paper whose headline exclusion is really a statement about how far the data sit above the SM, not a standalone measurement.

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arXiv ID0902.2393 (version 2)
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CitationA.G. Akeroyd, F. Mahmoudi. "Constraints on charged Higgs bosons from D(s)+- -> mu+- nu and D(s)+- -> tau+- nu." arXiv:0902.2393 (2009). https://pith.science/paper/UVWTN5RV
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The paper

The paper claims

Charged Higgs limits from charm-meson decays depend on one lattice number.

The reading

In the Standard Model the decays $D_s^+ -$> $mu^+ nu$ and $D_s^+ -$> $tau^+ nu$ proceed by annihilation into a $W$ boson, and their rates are proportional to the decay constant $f_{D_s}$ that lattice QCD is supposed to supply. A charged Higgs boson would add a second, tree-level route to the same final state, and in the Type II two-doublet model that extra route can only subtract from the rate, never add to it. The authors ask whether these charm decays, about to be measured far better at a dedicated charm facility, can do the job of the better-known probes $B^pm -$> $tau^pm nu$ and $K^pm -$> $mu^pm nu$: carve out a region in the plane of $tanbeta$ versus charged-Higgs mass. Their answer is yes, conditionally: the exclusion they obtain is comparable to, and in places complementary to, the kaon and B-meson ones, so long as the lattice value of $f_{D_s}$ is the small-error one near 241 MeV. If that holds, a charm experiment becomes a genuine probe of the Higgs sector rather than only a decay-constant measurement.

What carries the argument

The load-bearing object is the multiplicative factor $r_s$ that rescales the Standard Model width, $$r_s = left[1 + frac{1}{m_c+m_s} left(frac{M_{D_s}}{m_{H^+}}right)^2 left(m_c - frac{m_s $tan^{2}$$\beta$}{1+epsilon_0 tanbeta}right)right]^2,$$ entering $Gamma(D_s^pm -$> $ell^pm nu) = frac{G_F^2}{8pi} f_{D_s}^2 m_ell^2 M_{D_s} (1-m_ell^2/M_{D_s}^2)^2 |V_{cs}|^2, r_s$. The $m_s tan^2beta$ term is the strange-quark Yukawa coupling and is what makes the suppression grow with $tanbeta$; the $m_c$ piece comes from the charm Yukawa and is numerically negligible; $epsilon_0$ carries the loop-induced Type III admixture that appears in the MSSM and can reach order 0.01. Because the factor is squared and always enters with a minus sign relative to the Standard Model amplitude, the charged Higgs can only push the rate down, which is why an upward fluctuation in the data disfavours it. The same structure, with $m_K$ and $m_d/m_s$ in place of $M_{D_s}$ and $m_s/(m_c+m_s)$, produces the kaon observable $R^{ell}_{23} = |1 - (m_K^2/m_{H^+}^2)(1-m_d/m_s) tan^2beta/(1+epsilon_0 tanbeta)|$, which is the comparison target.

Extended reading notes

Core claim

The paper's claim is that the leptonic charm decays $D_s^pm -$> $mu^pm nu$ and $D_s^pm -$> $tau^pm nu$ give constraints on the charged-Higgs mass and $tanbeta$ that are competitive with, and complementary to, those from $B^pm -$> $tau^pm nu$ and from the kaon ratio $R^{ell}_{23}$. The authors implement the tree-level width with the Type II charged-Higgs factor $r_s$ in the publicly available code SuperIso, generate 50,000 points of the Non-Universal Higgs Mass MSSM, and project the surviving and excluded points onto the $[tanbeta, m_{H^+}]$ plane. With the Standard Model normalisation fixed by the lattice value $f_{D_s} = 241 pm 3$ MeV, the $D_s -$> $tau nu$ channel excludes a larger region of that plane than $R^{ell}_{23}$ does at 95% confidence, even for the least favourable quark-mass ratio $m_s/m_c = 0.04$, and it reaches the wedge where the charged-Higgs amplitude for $B^pm -$> $tau^pm nu$ cancels the Standard Model one and that decay alone cannot constrain. The authors are explicit that a sizeable charged-Higgs contribution can only suppress these rates, so the observed branching ratios, somewhat above the Standard Model prediction, cannot be explained this way; the point is not to explain the excess but to use the decays as a constraint.

Load-bearing premise

The exclusion rests entirely on adopting the lattice decay constant $f_{D_s} = 241 pm 3$ MeV from one calculation; the authors themselves note that repeating the analysis with $f_{D_s} = 248 pm 3 pm 8$ MeV leaves almost no constraint at all.

Editorial extensions

If this is right

  • At 95% confidence, $D_s^pm -$> $tau^pm nu$ excludes more of the $[tanbeta, m_{H^+}]$ plane than the kaon ratio $R^{ell}_{23}$ does, even with the pessimistic quark-mass ratio $m_s/m_c = 0.04$.
  • The charm decays reach the parameter wedge where the charged-Higgs amplitude in $B^pm -$> $tau^pm nu$ cancels the Standard Model contribution, a region that decay cannot constrain on its own.
  • A charm factory reducing both branching-ratio errors to a few percent would sharpen these constraints faster than the kaon ratio is likely to improve on the same timescale.
  • Because the rates are now implemented in SuperIso, the constraint propagates automatically into global fits of the MSSM parameter space alongside $b -$> $s gamma$ and $B_s -$> $mu^+mu^-$.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The whole charm-leptonic programme as a Higgs probe rises or falls with one lattice number: if $f_{D_s}$ settles above roughly 250 MeV, this channel leaves the constraint budget entirely and the field falls back on kaon and B decays.
  • Since a Type II charged Higgs can only suppress these rates, any excess that survives improved lattice calculations would have to come from elsewhere, and the paper's own list of alternatives, R-parity violation or leptoquarks, becomes the natural place to look.
  • The suppression scales with $m_s/(m_c+m_s)$, so a better lattice determination of the charm quark mass would tighten the bound without any new experimental data.
  • If a future experiment measures the rate precisely while lattice QCD independently fixes $f_{D_s}$, the two together would let one solve for the charged-Higgs contribution rather than merely bound it, turning a one-sided exclusion into a measurement.
Original abstract

The decays D(s)+- -> mu+- nu and D(s)+- -> tau+- nu have traditionally been used to measure the D(s)+- meson decay constant f_D(s). Recent measurements at CLEO-c and the B factories suggest a branching ratio for both decays somewhat higher than the Standard Model prediction using f_D(s) from unquenched lattice calculations. The charged Higgs boson (H+-) in the Two Higgs Doublet Model (Type II) would also mediate these decays, but any sizeable contribution from H+- can only suppress the branching ratios and consequently is now slightly disfavoured. It is shown that constraints on the parameters tan(beta) and m_H+- from such decays can be competitive with and complementary to analogous constraints derived from the leptonic meson decays B+- -> tau+- nu_tau and K+- -> mu+- nu_mu, especially if lattice calculations eventually prefer f_D(s) < 250 MeV.

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.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 3,840 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.53 · human participants 0.01 · controlled comparison 0.25 · randomized assignment 0.01 · states quantitative result 0.56 · compares with prior results 0.93 · mentions code or data availability 0.01.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

The decays D(s)+- -> mu+- nu and D(s)+- -> tau+- nu have traditionally been used to measure the D(s)+- meson decay constant f_D(s). Recent measurements at CLEO-c and the B factories suggest a branching ratio for both decays somewhat higher than the Standard Model prediction using f_D(s) from unquenched lattice calculations. The charged Higgs boson (H+-) in the Two Higgs Doublet Model (Type II) would also mediate these decays, but any sizeable contribution from H+- can only suppress the branching ratios and consequently is now slightly disfavoured. It is shown that constraints on the parameters tan(beta) and m_H+- from such decays can be competitive with and complementary to analogous constraints derived from the leptonic meson decays B+- -> tau+- nu_tau and K+- -> mu+- nu_mu, especially if lattice calculations eventually prefer f_D(s) < 250 MeV.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 The decays D(s)+- -> mu+- nu and D(s)+- -> tau+- nu have traditionally been used to measure the D(s)+- meson decay constant f_D(s). background 1.00 0.04 0.02 asserted 1.00
s1 Recent measurements at CLEO-c and the B factories suggest a branching ratio for both decays somewhat higher than the Standard Model prediction using f_D(s) from unquenched lattice calculations. background 0.95 0.05 0.03 hedged possibility 0.96
s2 The charged Higgs boson (H+-) in the Two Higgs Doublet Model (Type II) would also mediate these decays, but any sizeable contribution from H+- can only suppress the branching ratios and consequently is now slightly disfavoured. interpretation 0.45 0.20 0.38 asserted 0.60
s3 It is shown that constraints on the parameters tan(beta) and m_H+- from such decays can be competitive with and complementary to analogous constraints derived from the leptonic meson decays B+- -> tau+- nu_tau and K+- -> mu+- nu_mu, especially if lattice calculations eventually prefer f_D(s) < 250 MeV. result 0.43 0.82 0.80 asserted 0.85

What kind of paper the classifier reports this is: theoretical result 0.98 · evidence from literature 0.34.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Constraints on the plane [tan β, mH± ] from the decay D± s → τ ±ν for ms/mc = 0.04, 0.08 and 0.12 from top to bottom. Red points are excluded at 95% C.L. 9
Figure 2. Constraints on the plane [tan β, mH± ] from the decay D± s → µ ±ν for ms/mc = 0.04, 0.08 and 0.12 from top to bottom. Black points are excluded at 95% C.L. 10
Figure 3. Constraints on the plane [tan β, mH± ] from the observable Rℓ23 (which involves K± → µ ±ν/π ± → µ ±ν decays). Blue points are excluded at 95% C.L. (e.g., 99.7% C.L.) the constraints on the plane [tan β, mH± ] from BR(D± s → µ ±ν/τ ±ν) are weaker than those from Rℓ23 because the latter is measured more precisely. As pointed out in [42], one of the virtues of Rℓ23 is the fact that it can probe a region of plane [tan β, mH± ] which cannot be probed by the decay B± → τ ±ν (corresponding to the case of the H± induced amplitude for B± → τ ±ν being similar in size to that of the SM con
Figure 4. Regions of the plane [tan β, mA] in the NUHM model excluded by different flavour observables. The constraints are superimposed in the order given in the legend. emphasize that these decays should not be overlooked in phenomenological studies of H± in the MSSM and 2HDM (Type II). Finally we discuss the constraints on the plane [tan β, mH± ] from B physics observ￾ables. As discussed in the introduction, one-loop induced decays such as b → sγ [67] and B0 s → µ +µ − [68, 69] can give powerful constraints on the plane [tan β, mH± ] (e.g. [21, 44, 70, 71, 72]) although with a stronger…

Figures reproduced from arXiv:0902.2393 by the authors.

References
How the literature uses it

32 arXiv papers cite this in 37 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 24 sentences without a confident label

Uses its data or values 5 papers
Compares with it 1 paper
Cites it as background 7 papers
  • There have been many scenarios proposed, e.g. charged Higgs and/or leptoquark [ref] .

    Interpretation of the "$f_{D_s}$ puzzle" in SM and beyond · Introduction · 0.91

  • Using $Φ_1,2$, one can build the most general renormalizable $SU(2)_L ×U(1)_Y$ gauge invariant Higgs potential [ref] : [equation] By hermiticity of eq.

    H\to\gamma\gamma in the Complex Two Higgs Doublet Model · General c2HDM · 0.81

  • (With down squarks, the $d̃$ field should take a family index, and $κ$ and $κ'$ yet another index.) Exchange of $d̃$ generates Eq. ([ref]) with [equation] Generalizations of Eq. ([ref]) appear in non-Standard models that arise in many contexts [ref] .

    The f_{D_s} Puzzle · New Physics · 0.82

What it cites · 64 sentences without a confident label

Uses the method or tool of 2 papers
Uses data or values from 9 papers
Cites as background 5 papers

Discussion

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