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E. Lendvai

Publications and source records attributed to E. Lendvai.

At least 19 recordsLinked to original sources
arXiv2017

Quantum gravity corrections to gauge theories with a cutoff regularization

Gravity can be considered as an effective quantum field theory with reliable, but limited predictions. Though the influence of gravity on gauge and other interactions of elementary particles is still an open question. We calculate the lowest order quantum gravity contributions to the QED beta function in an effective field theory picture with a momentum cutoff. We use a recently proposed 4 dimensional improved momentum cutoff that preserves gauge and Lorentz symmetries. We find that there is a non-vanishing quadratic contribution to the photon 2-point function but after renormalization that does not lead to the running of the original coupling. We comment on corrections to the other gauge interactions and Yukawa couplings of heavy fermions. We argue that gravity cannot turn gauge interactions asymptotically free.

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arXiv2016

Diphoton excess and VV-scattering

We consider minimal effective interactions of the 750 GeV mass resonance observed recently by ATLAS and CMS. Assuming a new scalar and gauge invariant effective interactions leads to non-trivial two particle scattering amplitudes with asymptotic gauge boson states. The longitudinally polarized $W\pm$ and $Z$ bosons interacting via dimension-five effective operators provide stringent constraints on the validity of the effective model. The large width found by ATLAS implying a bound of approximately 500 GeV already below the resonance, turns this scenario unlikely. For production mainly in gluon fusion we get an upper bound of $\sim 1.3$ TeV and strong limits on the masses of the underlying vector-like fermions are given.

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arXiv2015

Doublet-singlet model and unitarity

We study the renormalizable singlet-doublet fermionic extension of the Standard Model. In this model, the new vector-like fermions couple to the gauge bosons and to the Higgs via new Yukawa couplings, that allow for nontrivial mixing in the new sector, providing a stable, neutral dark matter candidate. Approximate analytic formulae are given for the mass spectrum around the blind spots, where the dark matter candidate coupling to $h$ or $Z$ vanishes. We calculate the two particle scattering amplitudes in the model, impose the perturbative unitarity constraints and establish bounds on the Yukawa couplings.

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arXiv2015

Cutoff Regularization Method in Gauge Theories

A Lorentz and gauge symmetry preserving regularization method is discussed in four dimension based on momentum cutoff. We use the conditions of gauge invariance or equivalently the freedom of shift of the loop momentum to define the evaluation of the terms carrying even number of Lorentz indices, e.g. proportional to $k_μk_ν$. The remaining scalar integrals are calculated with a four dimensional momentum cutoff. The finite terms (independent of the cutoff) are free of ambiguities coming from subtractions in non-trivial cases. Finite parts of the result are equal with the results of dimensional regularization. The proposed method can be applied to various physical processes where the use of dimensional regularization is subtle or a physical cutoff is present. As a famous example it is shown that the triangle anomaly can be calculated unambiguously with this new improved cutoff.

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arXiv2013

Corrections to gauge theories in effective quantum gravity with a cutoff

We calculate the lowest order quantum gravity contributions to QED beta function in an effective field theory picture with a momentum cutoff. We use a recently proposed 4 dimensional improved momentum cutoff that preserves gauge and Lorentz symmetries. We find that there is non-vanishing quadratic contribution to the photon 2-point function but that does not lead to the running of the original coupling after renormalization. We argue that gravity cannot turn gauge theories asymptotically free.

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arXiv2011

Fermion Condensate as Higgs substitute

A dynamical symmetry breaking model of electroweak interactions is investigated based on strongly interacting fermions. Vector-like fermions of different representations of the weak SU(2) form a symmetry breaking condensate and generate the lepton and quark masses. The weak gauge bosons get their usual standard model masses from a gauge invariant effective Lagrangian of a doublet scalar field composed of the new fermion fields. Gap equations are derived and the conditions for finding a symmetry breaking solution are presented. The parameters of the model are constrained further by perturbative unitarity. The oblique electroweak corrections only slightly constrain the model. It is shown that the new charged fermions are produced at the next linear colliders in large number and the cross section for the LHC is presented.

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arXiv2010

Note on triangle anomaly with improved momentum cutoff

A Lorentz and gauge symmetry preserving regularization method has been proposed recently in 4 dimension based on Euclidean momentum cutoff. It is shown that the triangle anomaly can be calculated unambiguously with this new improved cutoff. The anticommutator of γ^{5} and γ^μ multiplied by five gamma is proportional to terms that do not vanish under a divergent loop-momentum integral, but cancel otherwise.

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arXiv2010

Symmetry preserving regularization with a cutoff

A Lorentz and gauge symmetry preserving regularization method is proposed in 4 dimension based on momentum cutoff. We use the conditions of gauge invariance or freedom of shift of the loop-momentum to define the evaluation of the terms carrying Lorentz indices, e.g. proportional to k_μk_ν. The remaining scalar integrals are calculated with a four dimensional momentum cutoff. The finite terms (independent of the cutoff) are unambiguous and agree with the result of dimensional regularization.

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arXiv2009

S and T Parameters in the Fermion Condensate Model

We calculate the oblique electroweak corrections and confront them with the experiments in a composite Higgs version of the standard model. A vector-like weak doublet and a singlet fermion are added to the standard model without elementary Higgs. Due to quartic coupling there is a mixing between the components of the new fields triggering electroweak symmetry breaking. The Peskin-Takeuchi S and T electroweak parameters are presented. The new sector of vector-like fermions is slightly constrained, T gives an upper bound on the mixing angle of the new fermions, which is already constrained by self-consistent gap-equations. S gives no constraints on the masses. This extension can give a positive contribution to T, allowing for a heavy Higgs boson in electroweak precision tests of the Standard Model.

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arXiv2008

Electroweak Precision Constraints on Vector-like Fermions

We calculate the oblique electroweak corrections and confront with the experiments in an extension of the Standard Model. The new fields added are a vector-like weak doublet and a singlet fermion. After electroweak symmetry breaking there is a mixing between the components of the new fields, but no mixing allowed with the standard fermions. Four electroweak parameters, $\hat{S}$, $\hat{T}$, W, Y are presented in the formalism of Barbieri et al., these are the generalization of the Peskin-Takeuchi S, T, U's. The vector-like extension is slightly constrained, $\hat{T}$ requires the new neutral fermion masses not to be very far from each other, allowing higher mass difference for higher masses and smaller mixing. $\hat{S}, W, Y$ gives practically no constraints on the masses. This extension can give a positive contribution to $\hat{T} $, allowing a heavy Higgs boson in electroweak precision tests of the Standard Model.

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arXiv2006

Gap Equations and Electroweak Symmetry Breaking

Recently a new dynamical symmetry breaking model of electroweak interactions was proposed based on interacting fermions. Two fermions of different SU(2) representations form a symmetry breaking condensate and generate the lepton and quark masses. The weak gauge bosons get their usual standard model masses from a gauge invariant Lagrangian of a composite doublet scalar field. The new fermion fields become massive by condensation. In this note the gap equations are given in the linearized (mean field) approximation and the conditions for symmetry breaking and mass generation are presented. Perturbative unitarity constrains the self-couplings and the masses of the new fermions, a raw spectrum is given.

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arXiv2005

Fermion Condensate Model of Electroweak Interactions

A new dynamical symmetry breaking model of electroweak interactions is proposed based on interacting fermions. Two fermions of different SU_{L}(2) representations form a symmetry breaking condensate and generate the lepton and quark masses. The weak gauge bosons get their usual standard model masses from a gauge invariant Lagrangian of a doublet scalar field composed of the new fermion fields. The new fermion fields become massive by condensation. It is shown that the new charged fermions are produced at the next linear colliders in large number. The model is a low energy one which cannot be renormalized perturbatively. For the parameters of the model unitarity constraints are presented.

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arXiv2004

Dynamical Symmetry Breaking with Vector Bosons

In the standard model of electroweak interactions the Higgs doublet is replaced by a complex vector doublet and a real vector singlet. The gauge symmetry is broken dynamically by a mixed condensate of the doublet and singlet vector fields. Gauge fields get their usual standard model masses by condensation. The new vector matter fields become massive by their gauge invariant selfcouplings and expected to have masses of few hundred GeV. Fermions are assigned to the gauge group in the usual manner. Fermion masses are coming from a gauge invariant fermion-vector field interaction by a mixed condensat, the Kobayashi-Maskawa description is unchanged. Perturbative unitarity estimates show that the model is valid up to 2-3 TeV. It is shown that from the new matter fields a large number of spin-one particle pairs is expected at future high energy e^{+}e^{-} linear colliders of 500-1500 GeV. The inclusive production cross section of new particle pairs is presented for hadron colliders, while at the Tevatron the new particle production is too low, at the LHC the yield is large.

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arXiv2004

Vector Condensate Model of Electroweak Interactions

In the standard model of electroweak interactions the Higgs doublet is replaced by a complex vector doublet and a real vector singlet. The gauge symmetry is broken dynamically by a mixed condensate of the doublet and singlet vector fields. Gauge fields get their usual standard model masses by condensation. The new vector matter fields become massive by their gauge invariant selfcouplings. Fermions are assigned to the gauge group in the usual manner. Fermion masses are coming from a gauge invariant fermion-vector field interaction by a mixed condensate. The Kobayashi-Maskawa description is unchanged. It is shown that from the new matter fields a large number of spin-one particle pairs is expected at future high energy e^{+}e^{-} linear colliders of 500-1500 GeV.

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arXiv2000

Resonance Production of Three Neutral Supersymmetric Higgs Bosons at LHC

Multiple production of Higgs particles is essential to study Higgs self-couplings at future high-energy colliders. In this paper we calculated the resonance contributions to the production of three lightest neutral supersymmetric Higgs bosons in gluon fusion at LHC. The cross sections due to trilinear Higgs couplings is sizeable but the measurement of the quartic coupling hhhH(h) seems to be impossible.

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arXiv1996

Testing the Vector Condensate Model of Electroweak Interactions at High Energy Hadron Colliders

In the vector condensate model a doublet of vector fields plays the role of the Higgs doublet of standard model and the gauge symmetry is broken dynamically. This results in a theory surviving the test of radiative corrections provided the new charged and neutral vector particles B have masses of at least several hundred GeV's. In this note we show that while at the Tevatron the heavy B-particle production is too low, at LHC the yield is large and, for instance, the inclusive cross section of $B^+ B^-$ pairs is 51.5 (15.3) fb at $\sqrt{s}=14$ TeV, $m_B=400(500)$ GeV.

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arXiv1995

OBLIQUE RADIATIVE CORRECTIONS IN THE VECTOR CONDENSATE MODEL OF ELECTROWEAK INTERACTIONS

Oblique radiative corrections are calculated to the parameter $S$ in a version of the standard model where the Higgs doublet is replaced by a doublet of vector bosons and the gauge symmetry is broken dynamically. We show that to each momentum scale there exists a domain of the masses of charged and neutral vector bosons where $S$ is compatible with the experiments. At a scale of 1 TeV this requires vector boson masses of at least $m_0 \approx $ 400--550 GeV, $ m_+ \approx $ 200--350 GeV.

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