arXiv subjects

G. Rupp

Publications and source records attributed to G. Rupp.

13 recordsLinked to original sources

arXiv2025

Reply to "There is no 690 GeV resonance"

A recent paper has criticised the idea that, beside the resonance of mass $m_h= 125$ GeV, the Higgs field might exhibit a relatively narrow, second resonance with a mass $M_H \sim 690$ GeV. Without considering the evidence we have provided, the criticism also concerned our claim that experimental signals for this new resonance might already be seen in some LHC data. Since our extensive work is covered by several papers, we will summarise here the whole issue, namely: i) the theoretical motivations for a two-mass structure in cutoff $\Phi^4$ theory; ii) the checks from lattice simulations and the prediction $(M_H)^{\rm Theor} = 690\,(30)$ GeV; iii) the present experimental indications of a new, relatively narrow resonance in the expected mass range. This compact presentation will thus give the elements to objectively judge on a relevant question of present-day particle physics.

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arXiv2025

The 690 GeV scalar resonance

Spontaneous symmetry breaking through the Higgs field has been experimentally confirmed as a basic ingredient of the Standard Model. However, the origin of the phenomenon may not be entirely clear, because, in perturbation theory, the vacuum turns out to be a metastable state. An alternative scenario was proposed that implies a second resonance of the Higgs field ${\cal H}$ with a well delimited mass $(M_H)^{\rm Theor} = 690\,(30)$ GeV. This stabilises the potential, but, owing to an $H$ coupling to longitudinal $W$s with the same typical strength as that of the low-mass state with $m_h= 125$ GeV, it would still remain a relatively narrow resonance. Our scope here is twofold. First, leaving out many details, we outline a simple logical path where the, apparently surprising, idea of such a second resonance follows from basic properties of $\Phi^4$ theories. Secondly, we spell out a definite experimental signature of this resonance that is clearly visible in various LHC data. As a by-product, the ${\cal H} ^3$ term gives $\kappa_\lambda = (M_H/m_h) \sim $ 5.5 consistently with the ATLAS and CMS data.

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arXiv2025

Additional evidence of a new 690 GeV scalar resonance

An alternative to the idea of a metastable electroweak vacuum would be an initial restriction to the pure scalar sector of the Standard Model, but describing spontaneous symmetry breaking consistently with studies indicating that there are two different mass scales in the problem: a mass scale $M_H$ associated with the zero-point energy and a mass scale $m_h$ defined by the quadratic shape of the potential at its minimum. Therefore, differently from perturbation theory where these two mass scales coincide, the Higgs field could exhibit a second resonance with mass $(M_H)^{\rm Theor} = 690\,(30)$ GeV. This stabilises the potential, but the heavy Higgs $H$ would couple to longitudinal $W$s with the same typical strength as the low-mass state with $m_h=125$ GeV and so would still remain a relatively narrow resonance. While interesting signals from LHC experiments were previously pointed out, we have now enlarged our data sample, sharpened the analysis of some final states, and noted correlations between different channels that point directly to such a second resonance. The combined statistical evidence, even if roughly estimated, is thus so large that the observed deviations from the background cannot represent statistical fluctuations.

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arXiv2023

Bottomonium vector resonances and threshold effects

The bottomonium spectrum is the perfect testing ground for the confining potential and unitarisation effects. The bottom quark is about three times heavier than the charm quark, so that $b\bar{b}$ systems probe primarily the short-range part of that potential. Also, the much smaller colour-hyperfine interaction in the $B$ mesons make the $B\bar{B}$ threshold lie significantly higher than the $D\bar{D}$ threshold in charmonium, on a relative scale of course. A further complicating circumstance is that none of the experimentally observed vector $b\bar{b}$ mesons has been positively identified as a $^{3\!}D_1$ state, contrary to the situation in charmonium. This makes definite conclusions about level splittings very problematic. Finally, there are compelling indications that the $Υ(10580)$ is not the $Υ(4S)$ state, as is generally assumed. Here we review an analysis of experimental bottomonium data which show indications of the two lowest and so far unlisted $^{3\!}D_1$ states below the $B\bar{B}$ threshold. Next an empirical modelling of vector $b\bar{b}$ resonances above the open-bottom threshold is revisited, based on the Resonance-Spectrum-Expansion production formalism applied to other experimental data. A recent effective-Lagrangian study supporting our non-resonant assignment of the $Υ(10580)$ is briefly discussed as well.

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arXiv2020

Strong evidence of $ρ(1250)$ from a unitary multichannel reanalysis of elastic scattering data with crossing-symmetry constraints

An analysis is presented of elastic $P$-wave $ππ$ phase shifts and inelasticities up to 2 GeV, aimed at identifying the corresponding $J^{PC}=1^{--}$ excited $ρ$ resonances and focusing on the $ρ(1250)$ vs. $ρ(1450)$ controversy. The approach employs an improved parametrization in terms of a manifestly unitary and analytic three-channel $S$-matrix with its complex-energy pole positions. The included channels are $ππ$, $\rho2π$, and $ρρ$, the latter two being effective in the sense that they mimic several experimentally observed decay modes with nearby thresholds. In an alternative fit, the $\rho2π$ mode is replaced by $ωπ$, which is also an experimentally relevant channel. The improvement with respect to prior work amounts to the enforcement of maximum crossing symmetry through once-subtracted dispersion relations called GKPY equations. A separate analysis concerns the pion electromagnetic form factor, which again demonstrates the enormous importance of guaranteeing unitarity and analyticity when dealing with very broad and highly inelastic resonances. In the case of $ρ(1250)$ vs. $ρ(1450)$, the failure to do so is shown to give rise to an error in the predicted mass of about 170 MeV. A clear picture emerges from these analyses, identifying five vector $ρ$ states below 2 GeV, viz. $ρ(770)$, $ρ(1250)$, $ρ(1450)$, $ρ(1600)$, and $ρ(1800)$, with $ρ(1250)$ being indisputably the most important excited $ρ$ resonance. The stability of the fits as well as the imposition of unitarity, analyticity, and approximate crossing symmetry in the analyses lend very strong support to these assignments. The possibly far-reaching consequences for meson spectroscopy are discussed.

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arXiv2012

Is the X(3872) a molecule?

Because of the controversial X(3872) meson's very close proximity to the $D^0\bar{D}^{*0}$ threshold, this charmonium-like resonance is often considered a meson-meson molecule. However, a molecular wave function must be essentially of a meson-meson type, viz. $D^0\bar{D}^{*0}$ in this case, with no other significant components. We address this issue by employing a simple two-channel Schrödinger model, in which the $J^{PC}=1^{++}$ $c\bar{c}$ and $D^0\bar{D}^{*0}$ channels can communicate via the $^3P_0$ mechanism, mimicked by string breaking at a sharp distance $a$. Thus, wave functions and their probabilities are computed, for different bound-state pole positions approaching the $D^0\bar{D}^{*0}$ threshold from below. We conclude that at the PDG X(3872) mass and for reasonable values of $a$, viz. 2.0 to 3.0 GeV$^{-1}$, the $c\bar{c}$ component remains quite substantial and certainly not negligible, despite accounting for only about 6 to 10% of the total wave-function probability, owing to the naturally long tail of the $D^0\bar{D}^{*0}$ component.

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arXiv2010

Coupled-channel analysis of the X(3872)

The X(3872) is studied as an axial-vector charmonium state in the multichannel framework of the Resonance-Spectrum-Expansion quark-meson model, previously applied to a variety of other puzzling mesonic resonances. Included are the open-charm pseudoscalar-vector and vector-vector channels, the most important of which is the S-wave $\bar{D}^{*0}D^{0}$ + $D^{*0}\bar{D}^{0}$ channel, which practically coincides with the X(3872) structure. The two free parameters of the model are tuned so as to roughly reproduce the $χ_{c1}(3511)$ mass as well as the enhancement just above the $\bar{D}^{*0}D^{0}$ / $D^{*0}\bar{D}^{0}$ threshold. The present model is able to describe the shape of the latter data quite well. However, as no dynamical resonance pole is found, the X(3872) and X(3940) cannot be reproduced simultaneously, at this stage. A possible further improvement is discussed.

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arXiv2009

The Nature of the X(2175)

We study the puzzling vector meson X(2175) in a multichannel generalisation of the Resonance-Spectrum-Expansion model. Besides the usual P-wave pseudoscalar-pseudoscalar, pseudoscalar-vector, and vector-vector channels that couple to mesons with vector quantum numbers, we also include the important S-wave vector-scalar, pseudoscalar-axialvector and vector-axialvector channels, including the observed $ϕ$(1020)$f_0$(980) decay mode. The strong coupling to nearby S-wave channels originates dynamically generated poles, two of which come out close to the energy region of the X(2175), viz. at (2.037-i0.170) GeV and (2.382-i0.20) GeV. Further improvements are proposed.

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arXiv2007

A low-lying scalar meson nonet in a unitarized meson model

A unitarized nonrelativistic meson model which is successful for the description of the heavy and light vector and pseudoscalar mesons yields, in its extension to the scalar mesons but for the same model parameters, a complete nonet below 1 GeV. In the unitarization scheme, real and virtual meson-meson decay channels are coupled to the quark-antiquark confinement channels. The flavor-dependent harmonic-oscillator confining potential itself has bound states epsilon(1.3 GeV), S(1.5 GeV), delta(1.3 GeV), kappa(1.4 GeV), similar to the results of other bound-state qqbar models. However, the full coupled-channel equations show poles at epsilon(0.5 GeV), S(0.99 GeV), delta(0.97 GeV), kappa(0.73 GeV). Not only can these pole positions be calculated in our model, but also cross sections and phase shifts in the meson-scattering channels, which are in reasonable agreement with the available data for pion-pion, eta-pion and Kaon-pion in S-wave scattering.

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arXiv2007

Constituent and current quark masses at low chiral energies

Light constituent quark masses and the corresponding dynamical quark masses are determined by data, the Quark-Level Linear $σ$ Model, and infrared QCD. This allows to define effective nonstrange and strange current quark masses which reproduce the experimental pion and kaon masses very accurately, by simple additivity. Moreover, the masses of the light scalar mesons $σ(600)$ and $κ(800)$ can be obtained straightforwardly from the constituent quark masses. In contrast, the usual nonstrange and strange current quark masses employed by Chiral Perturbation Theory do not allow a simple quantitative explanation of the pion and kaon masses.

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arXiv2006

The nature of $σ$, $κ$, $a_0(980)$ and $f_0(980)$

Masses and widths of the four light scalar mesons $σ$, $κ$, $a_0$(980) and $f_0$(980) may be reproduced in a model where mesons scatter via a $q\bar{q}$ loop. A transition potential is used to couple mesons to $q\bar{q}$ at a radius of $\sim 0.57$ fm. Inside this radius, there is an infinite bare spectrum of confined $q\bar{q}$ states, for which a harmonic oscillator is chosen here. The coupled-channel system approximately reproduces the features of both light and heavy meson spectroscopy. The generation of $σ$, $κ$, $a_0(980)$ and $f_0(980)$ is a balance between attraction due to the $q\bar q$ loop and suppression of the amplitudes at the Adler zeros. Phase shifts increase more rapidly as the coupling constant to the mesons increases. This leads to resonant widths which decrease with increasing coupling constant - a characteristically non-perturbative effect.

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arXiv2006

Constituent Quark Masses and the Electroweak Standard Model

Constituent quark masses can be determined quite well from experimental data in several ways and one can obtain fairly accurate values for all six $m_q$. The strong quark-meson coupling $g=2π/\sqrt{3}$ arises from the quark-level linear $σ$ model, whereas $e$ and $\sinθ_w$ arise from weak interactions when the heavy $M_W$ and $M_Z$ are regarded as resonances in analogy with the strong KSFR relation. The Higgs boson mass, tied to null expectation value of charged Higgs components, is found to be around 317 GeV. Finally, the experimental CPV phase angle $δ$ and the three CKM angles $Θ_c, Θ_2, Θ_3$ are successfully deduced from the 6 constituent quark masses following Fritzsch's approach.

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arXiv2003

SU(3) Mass Splittings for $\bar{q}q$ Mesons and $qqq$ Baryons

By comparing SU(3)-breaking scales of linear mass formulae, it is shown that the lowest vector, axial-vector, and scalar mesons all have a $\bar{q}q$ configuration, while the ground-state octet and decuplet baryons are $qqq$. Also, the quark-level linear $σ$ model is employed to predict similar $\bar{q}q$ and $qqq$ states. Finally, the approximate mass degeneracy of the scalar $a_0$(980) and $f_0$(980) mesons is demonstrated to be accidental.

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