arXiv subjects

Ulrich Nierste

Publications and source records attributed to Ulrich Nierste.

At least 55 records · Page 3Linked to original sources

arXiv2017

Towards next-to-next-to-leading-log accuracy for the width difference in the $B_s-\bar{B}_s$ system: fermionic contributions to order $(m_c/m_b)^0$ and $(m_c/m_b)^1$

We calculate a class of three-loop Feynman diagrams which contribute to the next-to-next-to-leading logarithmic approximation for the width difference $ΔΓ_{s}$ in the $B_s-\bar{B}_s$ system. The considered diagrams contain a closed fermion loop in a gluon propagator and constitute the order $α_s^2 N_f$, where $N_f$ is the number of light quarks. Our results entail a considerable correction in that order, if $ΔΓ_{s}$ is expressed in terms of the pole mass of the bottom quark. If the $\overline{MS}$ scheme is used instead, the correction is much smaller. As a result, we find a decrease of the scheme dependence. Our result also indicates that the usually quoted value of the NLO renormalization scale dependence underestimates the perturbative error.

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arXiv2017

$K\to πν\overlineν$ in the MSSM in Light of the $ε^{\prime}_K/ε_K$ Anomaly

The Standard-Model (SM) prediction for the CP-violating quantity $ε_K^{\prime}/ε_K$ deviates from its measured value by 2.8 $σ$. It has been shown that this tension can be resolved within the Minimal Supersymmetric Standard Model (MSSM) through gluino-squark box diagrams, even if squarks and gluinos are much heavier than 1 TeV. The rare decays $K_L \to π^0ν\barν$ and $K^+ \to π^+ν\barν$ are similarly sensitive to very high mass scales and the first one also measures CP violation. In this article, we analyze the correlations between $ε^{\prime}_K/ε_K$ and $B(K_L \to π^0ν\barν)$ and $B(K^+ \to π^+ν\barν)$ within the MSSM aiming at an explanation of $ε_K^{\prime}/ε_K$ via gluino-squark box diagrams. The dominant MSSM contribution to the $K \to πν\barν$ branching fractions stems from box diagrams with squarks, sleptons, charginos, and neutralinos, and the pattern of the correlations is different from the widely studied $Z$-penguin scenarios. This is interesting in light of future precision measurements by KOTO and NA62 at J-PARC and CERN, respectively. We find $B(K_L \to π^0ν\barν)/B^{SM} (K_L \to π^0ν\barν)\lesssim 2\,(1.2)$ and $B(K^+ \to π^+ν\barν)/B^{SM}(K^+ \to π^+ν\barν) \lesssim 1.4\,(1.1)$, if all squark masses are above 1.5 TeV, gaugino masses obey GUT relations, and if one allows for a fine-tuning at the $1\%\,(10\%)$ level for the gluino mass. Larger values are possible for a tuned CP violating phase. Furthermore, the sign of the MSSM contribution to $ε_K^{\prime}$ imposes a strict correlation between $B(K_L \to π^0ν\barν)$ and the hierarchy between the masses $m_{\bar{U}}$, $m_{\bar{D}}$ of the right-handed up-squark and down-squark: sgn$[B(K_L \to π^0ν\barν)-B^{SM} (K_L \to π^0ν\barν)] = $sgn$(m_{\bar{U}}-m_{\bar{D}}) $.

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arXiv2017

$ε_K^\prime/ε_K$: Standard Model and Supersymmetry

I give a pedagogical introduction into flavour-changing neutral current interactions of kaons and their role to reveal or constrain physics beyond the Standard Model (SM). Then I discuss the measure $ε_K^\prime$ of direct CP violation in $K\to ππ$ decays, which deviates from the SM prediction by $2.8σ$. A supersymmetric scenario with flavour mixing among left-handed squarks can accomodate the measured value of $ε_K^\prime$ even for very heavy sparticles, outside the reach of the LHC. The considered scenario employs mass splittings among the right-handed up and down squarks (to enhance $ε_K^\prime$) and a gluino which is heavier than the left-handed strange-down mixed squarks by at least a factor of 1.5 (to suppress excessive contribution to $ε_K$, the measure of indirect CP violation). The branching ratios of the rare decays $K^+ \to π^+ ν\barν$ and $K_L \to π^0 ν\barν$, to be measured by the NA62 and KOTO-step2 experiments, respectively, are only moderately affected. These measurements have the capability to either falsify the model or to constrain the CP phase associated with strange-down squark mixing accurately.

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arXiv2017

CP asymmetries in $D\to PP^\prime$ decays

This talk addresses two topics related to CP asymmetries in $D$ meson decays to two pseudoscalar mesons. First I discuss how new physics can be distinguished from the Standard Model through two sum rules relating three direct CP asymmetries each, using the sum rule correlating $D^0\to K^+K^-$, $D^0\to π^+ π^-$, and $D^0\to π^0 π^0$ for illustration. The other sum rule involves $a_{CP}^{\mathrm{dir}}(D^+\rightarrow \bar{K}^0K^+)$, $a_{CP}^{\mathrm{dir}}(D_s^+\rightarrow K^0π^+)$, and $a_{CP}^{\mathrm{dir}}(D_s^+\to K^+ π^0)$. The second topic is the direct CP asymmetry in the decay $D^0 \to K_S K_S$, which is expected to be large in the Standard Model for two reasons: Flavor-SU(3) symmetry suppresses the tree amplitude which enhances the crucial "penguin-to-tree" ratio and the "penguin" amplitude is dominated by the tree-level $W$ boson exchange between $c$ and $u$ quarks. We find that $|a_{CP}^{\mathrm{dir}} (D^0 \to K_S K_S)|$ can be as large as $1.1 \%$ in the Standard Model. We advocate $D^0 \to K_S K_S$ as a discovery channel for charm CP violation.

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arXiv2017

Penguin pollution in $β$ and $β_s$

The mixing-induced CP asymmetries in $B_d \to J/ψK_S$ and $B_s \to J/ψϕ$ are essential to detect or constrain new physics in the $B_d\! - \overline{\!B}{}_d$ and $B_s\! - \overline{\!B}{}_s$ mixing amplitudes, respectively. To this end one must control the penguin contributions to the decay amplitudes, which affect the extraction of fundamental CP phases from the measured CP asymmetries. Although the "penguin pollution" is doubly Cabibbo-suppressed, it could compete in size with current experimental errors. In this talk I present a calculation of the penguin contributions treating QCD effects with soft-collinear factorisation and compare method and results with the alternative approach employing flavour-SU(3) symmetry. As a novel feature, I present results for the penguin pollution in $b\to c\overline c d$ modes.

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arXiv2016

Direct CP violation in $K\to ππ$ decays and supersymmetry

The quantities $ε_K^\prime$ and $ε_K$ measure the amount of direct and indirect CP violation in $K\to ππ$ decays, respectively. Using the recent lattice results from the RBC and UKQCD Collaborations and a new compact implementation of the $ΔS=1$ renormalization group evolution we predict $ \mbox{Re}\, \frac{ε_{K}'}{ε_{K}} = \left(1.06 \pm 5.07 \right) \times 10^{-4}$ in the Standard Model. This value is $2.8\,σ$ below the experimental value of $ \mbox{Re}\, \frac{ε_{K}'}{ε_{K}} = \left(16.6 \pm 2.3 \right) \times 10^{-4}.$ In generic models of new physics the well-understood $ε_K$ precludes large contributions to $ε_K^\prime$, if the new contributions enter at loop level. However, one can resolve the tension in $ε_{K}'/ε_{K}$ within the Minimal Supersymmetric Standard Model. To this end two features of supersymmetry are crucial: First, one can have large isospin-breaking contributions (involving the strong instead of the weak interaction) which enhance $ε_K^\prime$. Second, the Majorana nature of gluinos permits a suppression of the MSSM contribution to $ε_K$, because two box diagrams interfere destructively.

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arXiv2016

Singularity-free Next-to-leading Order $ΔS= 1$ Renormalization Group Evolution and $ε_{K}^{\prime}/ε_{K}$ in the Standard Model and Beyond

The standard analytic solution of the renormalization group (RG) evolution for the $ΔS = 1$ Wilson coefficients involves several singularities, which complicate analytic solutions. In this paper we derive a singularity-free solution of the next-to-leading order (NLO) RG equations, which greatly facilitates the calculation of $ε_K^{\prime}$, the measure of direct $CP$ violation in $K\to ππ$ decays. Using our new RG evolution and the latest lattice results for the hadronic matrix elements, we calculate the ratio $ε_{K}^{\prime}/ε_{K}$ (with $ε_{K}$ quantifying indirect $CP$ violation) in the Standard Model (SM) at NLO to $ε_{K}^{\prime}/ε_{K} = (1.06 \pm 5.07) \times 10^{-4} $, which is $2.8\,σ$ below the experimental value. We also present the evolution matrix in the high-energy regime for calculations of new physics contributions and derive easy-to-use approximate formulae. We find that the RG amplification of new-physics contributions to Wilson coefficients of the electroweak penguin operators is further enhanced by the NLO corrections: If the new contribution is generated at the scale of 1-10 TeV, the RG evolution between the new-physics scale and the electroweak scale enhances these coefficients by 50-100 %. Our solution contains a term of order $α_{EM}^2/α_s^2$, which is numerically unimportant for the SM case but should be included in studies of high-scale new-physics.

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arXiv2016

Recent progress on CP violation in $K\to ππ$ decays in the SM and a supersymmetric solution

Using the recent first lattice results of the RBC-UKQCD collaboration for $K \to ππ$ decays, we perform a phenomenological analysis of $ε_K^{\prime}/ε_K$ and find a discrepancy between SM prediction and experiments by $\sim 3\,σ$. We discuss an explanation by new physics. The well-understood value of $ε_K$, which quantifies indirect $CP$ violation, however, typically prevents large new physics contributions to $ε_K^{\prime}/ε_K$. In this talk, we show a solution of the $ε_K^{\prime}/ε_K$ discrepancy in the Minimal Supersymmetric Standard Model with squark masses above 3 TeV without fine-tuning of $CP$ phases. In this solution, the Trojan penguin diagram gives large isospin-breaking contributions which enhance $ε_K^{\prime}$, while the contribution to $ε_K$ is suppressed thanks to the Majorana nature of gluinos.

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arXiv2016

Supersymmetric Explanation of CP Violation in $K\to ππ$ Decays

Recent progress in the determination of hadronic matrix elements has revealed a tension between the measured value of $ε_K^{\prime}/ε_K$, which quantifies direct $CP$ violation in $K \to ππ$ decays, and the Standard-Model prediction. The well-understood indirect $CP$ violation encoded in the quantity $ε_K$ typically precludes large new-physics contributions to $ε_K^{\prime}/ε_K$ and challenges such an explanation of the discrepancy. We show that it is possible to cure the $ε_K^{\prime}/ε_K$ anomaly in the Minimal Supersymmetric Standard Model with squark masses above 3 TeV without overshooting $ε_K$. This solution exploits two features of supersymmetry: the possibility of large isospin-breaking contributions (enhancing $ε_K^{\prime}$) and the Majorana nature of gluinos (permitting a suppression of $ε_K$). Our solution involves no fine-tuning of $CP$ phases or other parameters.

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arXiv2016

Charm Quark Contribution to K+ -> pi+ nu anti-nu at Next-to-Next-to-Leading Order

We calculate the complete NNLO QCD corrections to the charm contribution of the rare decay K+ -> pi+ nu nu-bar. We encounter several new features, which were absent in lower orders. We discuss them in detail and present the results for the 2-loop matching conditions of the Wilson coefficients, the 3-loop anomalous dimensions, and the 2-loop matrix elements of the relevant operators that enter the NNLO renormalization group analysis of the Z-penguin and the electroweak box contribution. The inclusion of the NNLO QCD corrections leads to a significant reduction of the theoretical uncertainty from 9.8% down to 2.4% in the relevant parameter Pc, implying the leftover scale uncertainties in BR(K+ -> pi+ nu nu-bar) and in the determination of |V_td|, sin(2 beta), and gamma from the K -> pi nu nu system to be 1.3%, 1.0%, 0.006, and 1.2 degrees, respectively. For the charm quark MSbar mass mc=(1.30+-0.05) GeV and |V_us|= 0.2248 the NLO value Pc=0.37+-0.06 is modified to Pc=0.38+-0.04 at the NNLO level with the latter error fully dominated by the uncertainty in mc. We present tables for Pc as a function of mc and alphas(MZ) and a very accurate analytic formula that summarizes these two dependences as well as the dominant theoretical uncertainties. Adding the recently calculated long-distance contributions we find BR(K+ -> pi+ nu nu-bar)=(8.0+-1.1)*10^-11 with the present uncertainties in mc and the Cabibbo-Kobayashi-Maskawa elements being the dominant individual sources in the quoted error. We also emphasize that improved calculations of the long-distance contributions to K+ -> pi+ nu nu-bar and of the isospin breaking corrections in the evaluation of the weak current matrix elements from K+ -> pi0 e+ nu would be valuable in order to increase the potential of the two golden K -> pi nu nu decays in the search for new physics.

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arXiv2015

Sum Rules of Charm CP Asymmetries beyond the SU(3)$_F$ Limit

We find new sum rules between direct CP asymmetries in $D$ meson decays with coefficients that can be determined from a global fit to branching ratio data. Our sum rules eliminate the penguin topologies $P$ and $PA$, which cannot be determined from branching ratios. In this way we can make predictions about direct CP asymmetries in the standard model without ad hoc assumptions on the sizes of penguin diagrams. We consistently include first-order SU(3)$_F$ breaking in the topological amplitudes extracted from the branching ratios. By confronting our sum rules with future precise data from LHCb and Belle~II one will identify or constrain new-physics contributions to $P$ or $PA$. The first sum rule correlates the CP asymmetries $a_{CP}^{\mathrm{dir}}$ in $D^0\to K^+K^-$, $D^0\to π^+π^-$, and $D^0\to π^0π^0$. We study the region of the $a_{CP}^{\mathrm{dir}}(D^0\to π^+π^-)$--$a_{CP}^{\mathrm{dir}} (D^0\to π^0π^0)$ plane allowed by current data and find that our sum rule excludes more than half of the allowed region at 95\% C.L. Our second sum rule correlates the direct CP asymmetries in $D^+\rightarrow \bar{K}^0 K^+$, $D_s^+\rightarrow K^0 π^+$, and $D_s^+\rightarrow K^+π^0$.

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arXiv2015

CP Violation in $D^0\rightarrow K_SK_S$

The direct CP asymmetry $a_{CP}^{\mathrm{dir}}(D^0\rightarrow K_SK_S)$ involves exchange diagrams which are induced at tree level in the Standard Model. Since the corresponding topological amplitude $E_{KK}$ can be large, $D^0\rightarrow K_SK_S$ is a promising discovery channel for charm CP violation. We estimate the penguin annihilation amplitude with a perturbative calculation and extract the exchange amplitude $E_{KK}$ from a global fit to $D$ branching ratios. Our results are further used to predict the size of mixing-induced CP violation. We obtain $\vert a_{CP}^{\mathrm{dir}}(D^0\rightarrow K_SK_S)\vert \leq 1.1\%$ (95\% C.L.). The same bound applies to the nonuniversal part of the phase between the $D\!-\overline{\!D}\,$ mixing and decay amplitudes. If future data exceed our predictions, this will point to new physics or an enhancement of the penguin annihilation amplitude by QCD dynamics. We briefly discuss the implications of these possibilities for other CP asymmetries.

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arXiv2015

Lepton-flavour violating $B$ decays in generic $Z^\prime$ models

LHCb has reported deviations from the Standard Model in $b\to sμ^+μ^-$ transitions for which a new neutral gauge boson is a prime candidate for an explanation. As this gauge boson has to couple in a flavour non-universal way to muons and electrons in order to explain $R_K$, it is interesting to examine the possibility that also lepton flavour is violated, especially in the light of the CMS excess in $h\toτ^\pmμ^\mp$. In this article, we investigate the perspectives to discover the lepton-flavour violating modes $B\to K^{(*)}τ^\pmμ^\mp$, $B_s\to τ^\pmμ^\mp$ and $B\to K^{(*)} μ^\pm e^\mp$, $B_s\to μ^\pm e^\mp$. For this purpose we consider a simplified model in which new-physics effects originate from an additional neutral gauge boson ($Z^\prime$) with generic couplings to quarks and leptons. The constraints from $τ\to3μ$, $τ\toμν\barν$, $μ\to eγ$, $g_μ-2$, semi-leptonic $b\to sμ^+μ^-$ decays, $B\to K^{(*)}νν$ and $B_s$--$\overline{B}_s$ mixing are examined. From these decays, we determine upper bounds on the decay rates of lepton flavour violating $B$ decays. $Br(B\to Kνν)$ limits the branching ratios of LFV $B$ decays to be smaller than $8\times 10^{-5} (2\times 10^{-5})$ for vectorial (left-handed) lepton couplings. However, much stronger bounds can be obtained by a combined analysis of $B_s$--$\overline{B}_s$, $τ\to3μ$, $τ\toμν\barν$ and other rare decays. The bounds depend on the amount of fine-tuning among the contributions to $B_s$--$\overline{B}_s$ mixing. Allowing for a fine-tuning at the percent level we find upper bounds of the order of $10^{-6}$ for branching ratios into $τμ$ final states, while $B_s\to μ^\pm e^\mp$ is strongly suppressed and only $B\to K^{(*)} μ^\pm e^\mp$ can be experimentally accessible (with a branching ratio of order $10^{-7}$).

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arXiv2015

Vacuum stability of the effective Higgs potential in the Minimal Supersymmetric Standard Model

The parameters of the Higgs potential of the Minimal Supersymmetric Standard Model (MSSM) receive large radiative corrections which lift the mass of the lightest Higgs boson to the measured value of 126 GeV. Depending on the MSSM parameters, these radiative corrections may also lead to the situation that the local minimum corresponding to the electroweak vacuum state is not the global minimum of the Higgs potential. We analyze the stability of the vacuum for the case of heavy squark masses as favored by current LHC data. To this end we first consider an effective Lagrangian obtained by integrating out the heavy squarks and then study the MSSM one-loop effective potential V_eff, which comprises all higher-dimensional Higgs couplings of the effective Lagrangian. We find that only the second method gives correct results and argue that the criterion of vacuum stability should be included in phenomenological analyses of the allowed MSSM parameter space. Discussing the cases of squark masses of 1 and 2 TeV we show that the criterion of vacuum stability excludes a portion of the MSSM parameter space in which (mu tanbeta) and A_t are large.

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arXiv2015

Penguin contributions to CP phases in $B_{d,s}$ decays to charmonium

The precision of the CP phases $2β$ and $2β_s$ determined from the mixing-induced CP asymmetries in $B_d\to J/ψK_S$ and $B_s\to J/ψϕ$, respectively, is limited by the unknown long-distance contribution of a penguin diagram involving up quarks. The penguin contribution is expected to be comparable in size to the precision of the LHCb and Belle II experiments and therefore limits the sensitivity of the measured quantities to new physics. We analyze the infrared QCD structure of this contribution and find that all soft and collinear divergences either cancel between different diagrams or factorize into matrix elements of local four-quark operators up to terms suppressed by $Λ_{QCD}/m_ψ$, where $m_ψ$ denotes the $J/ψ$ mass. Our results, which are based on an operator product expansion, allow us to calculate the penguin-to-tree ratio $P/T$ in terms of the matrix elements of these operators and to constrain the penguin contribution to the phase $2β$ as $|Δϕ_d|\leq {0.68}^\circ$. The penguin contribution to $2β_s$ is bounded as $|Δϕ_s^{0}|\leq {0.97}^\circ$, $|Δϕ_s^{\parallel}|\leq {1.22}^\circ$, and $|Δϕ_s^{\perp}|\leq {0.99}^\circ$ for the case of longitudinal, parallel, and perpendicular $ϕ$ and $J/ψ$ polarizations, respectively. We further place bounds on $|Δϕ_d|$ for $B_d\to ψ(2S) K_S$ and the polarization amplitudes in $B_d\to J/ψK^*$. In our approach it is further possible to constrain $P/T$ for decays in which $P/T$ is Cabibbo-unsuppressed and we derive upper limits on the penguin contribution to the mixing-induced CP asymmetries in $B_d\to J/ψπ^0$, $B_d\to J/ψρ^0$, $B_s\to J/ψK_S$, and $B_s\to J/ψK^*$. For all studied decay modes we also constrain the sizes of the direct CP asymmetries.

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arXiv2015

Topological amplitudes in $D$ decays to two pseudoscalars: a global analysis with linear $SU(3)_F$ breaking

We study decays of $D^0$, $D^+$, and $D_s^+$ mesons into two pseudoscalar mesons by expressing the decay amplitudes in terms of topological amplitudes. Including consistently SU(3)$_F$ breaking to linear order, we show how the topological-amplitude decomposition can be mapped onto the standard expansion using reduced amplitudes characterized by SU(3) representations. The tree and annihilation amplitudes can be calculated in factorization up to corrections which are quadratic in the color-counting parameter $1/N_c$. We find new sum rules connecting $D^+\rightarrow K_SK^+$, $D_s^+\rightarrow K_Sπ^+$ and $D^+\rightarrow K^+π^0$, which test the quality of the $1/N_c$ expansion. Subsequently, we determine the topological amplitudes in a global fit to the data, taking the statistical correlations among the various measurements into account. We carry out likelihood ratio tests in order to quantify the role of specific topological contributions. While the SU(3)$_F$ limit is excluded with a significance of more than five standard deviations, a good fit (with $Δχ^2 <1$) can be obtained with less than $28\%$ of SU(3)$_F$ breaking in the decay amplitudes. The magnitude of the penguin amplitude $P_{\mathrm{break}}$, which probes the Glashow Iliopoulos Maiani (GIM) mechanism, is consistent with zero; the hypothesis $P_{\mathrm{break}}=0$ is rejected with a significance of just $0.7σ$. We obtain the Standard-Model correlation between $\mathcal{B}(D^0\rightarrow K_L π^0)$ and $\mathcal{B}(D^0\rightarrow K_Sπ^0)$, which probes doubly Cabibbo-suppressed amplitudes, and find that $\mathcal{B}(D^0\rightarrow K_L π^0)<\mathcal{B}(D^0\rightarrow K_Sπ^0)$ holds with a significance of more than $4σ$. We finally predict $\mathcal{B}(D_s^+\rightarrow K_L K^+)= 0.012^{+0.006}_{-0.002}$ at $3σ$ CL.

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arXiv2014

Benchmarks for Higgs Pair Production and Heavy Higgs Searches in the Two-Higgs-Doublet Model of Type II

The search for additional Higgs particles and the exact measurements of Higgs (self-) couplings is a major goal of future collider experiments. In this paper we investigate the possible sizes of new physics signals in these searches in the context of the $CP$-conserving two-Higgs doublet model of type II. Using current constraints from flavour, electroweak precision, and Higgs signal strength data, we determine the allowed sizes of the triple Higgs couplings and the branching fractions of the heavy Higgs bosons into lighter Higgs bosons. Identifying the observed Higgs resonance with the light $CP$-even 2HDM Higgs boson $h$, we find that the $hhh$ coupling cannot exceed its SM value, but can be reduced by a factor of $0.56$ at the 2 $σ$ level. The branching fractions of the heavy neutral Higgs bosons $H$ and $A$ into two-fermion or two-vector-boson final states can be reduced by factors of $0.4$ and $0.01$, respectively, if decays into lighter Higgs boson are possible and if the mass of the decaying Higgs is below the $t\bar t$ threshold. To facilitate future studies of collider signatures in 2HDM scenarios with large triple Higgs couplings or decay modes of the heavy Higgs bosons not covered by the SM Higgs searches we provide a set of benchmark points which exhibit these features and agree with all current constraints. We also discuss the effect of the heavy Higgs bosons on the $gg\to hh$ cross section at a 14 TeV LHC for some of these benchmarks. For $m_H$ below the $hh$ threshold we see a reduction of the SM $gg\to hh$ cross section due to destructive interference, but for $m_H$ above the $hh$ threshold current constraints allow enhancement factors above 50. An enhancement factor of 6 is still possible in scenarios in which the heavy Higgs particles would not be discovered by standard searches after 300 fb${}^{-1}$ of data.

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arXiv2013

Status of the two-Higgs-doublet model of type II

We determine the allowed parameter space of the CP-conserving two-Higgs-doublet model (2HDM) of type II with a softly broken Z_2 symmetry. Our analysis includes theoretical constraints from vacuum stability and perturbativity as well as experimental constraints from signal strengths of the 126 GeV Higgs boson, the non-observation of additional Higgs resonances and electroweak precision and flavour observables. If the 126 GeV resonance is interpreted as the light CP-even Higgs boson of the 2HDM our analysis shows that scenarios where the couplings of this boson deviate substantially from those of the SM Higgs boson are disfavoured at one standard deviation and completely excluded for small values of tan(beta). We also discuss bounds on the masses of the heavy 2HDM Higgs bosons and their implications for the possible decay modes of these particles. We find that the region in which both non-standard neutral Higgs bosons are simultaneously lighter than 300 GeV is excluded at two standard deviations.

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