arXiv subjects

D. Kekez

Publications and source records attributed to D. Kekez.

At least 19 recordsLinked to original sources

arXiv2014

A $U_A(1)$ symmetry restoration scenario supported by the generalized Witten-Veneziano relation and its analytic solution

The Witten-Veneziano relation, or, alternatively, its generalization proposed by Shore, facilitates understanding and describing the complex of eta and eta' mesons. We present an analytic, closed-form solution to Shore's equations which gives results on the eta-eta' complex in full agreement with results previously obtained numerically. Although the Witten-Veneziano relation and Shore's equations are related, the ways they were previously used in the context of dynamical models to calculate eta and eta' properties, were rather different. However, with the analytic solution, the calculation can be formulated similarly to the approach through the Witten-Veneziano relation, and with some conceptual improvements. In the process, one strengthens the arguments in favor of a possible relation between the U_A(1) and SU_A(3) chiral symmetry breaking and restoration. To test this scenario, the experiments such as those at RHIC, NICA and FAIR, which extend the RHIC (and LHC) high-temperature scans also to the finite-density parts of the QCD phase diagram, should pay particular attention to the signatures from the eta'-eta complex indicating the symmetry restoration.

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arXiv2013

eta' multiplicity and Witten-Veneziano relation at T>0

Recent RHIC results on eta' multiplicity in heavy-ion collisions are of great importance because they clearly signal a partial restoration of U_A(1) symmetry at high temperatures T, and thus provide an unambiguous signature of the formation of a new state of matter. Prompted by these experimental results of STAR and PHENIX collaborations, we discuss and propose the minimal generalization of the Witten-Veneziano relation to finite T.

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arXiv2013

Constraining solar hidden photons using HPGe detector

In this Letter we report on the results of our search for photons from a U(1) gauge factor in the hidden sector of the full theory. With our experimental setup we observe the single spectrum in a HPGe detector arising as a result of the photoelectric-like absorption of hidden photons emitted from the Sun on germanium atoms inside the detector. The main ingredient of the theory used in our analysis, a severely constrained kinetic mixing from the two U(1) gauge factors and massive hidden photons, entails both photon into hidden state oscillations and a minuscule coupling of hidden photons to visible matter, of which the latter our experimental setup has been designed to observe. On a theoretical side, full account was taken of the effects of refraction and damping of photons while propagating in Sun's interior as well as in the detector. We exclude hidden photons with kinetic couplings chi > (2.2 x 10^{-13}- 3 x 10^{-7}) in the mass region 0.2 eV < m_gamma' < 30 keV. Our constraints on the mixing parameter chi in the mass region from 20 eV up to 15 keV prove even slightly better then those obtained recently by using data from the CAST experiment, albeit still somewhat weaker than those obtained from solar and HB stars lifetime arguments.

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arXiv2012

Restoration of singlet axial symmetry at finite temperature

To accomodate recent RHIC data on eta prime multiplicity, we propose a minimal modification of the Witten-Veneziano relation at high temperature. This renders a significant drop of eta prime mass at high temperature signaling a restoration of the U(1)A, and the Goldstone character of etaprime.

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arXiv2011

η' Multiplicity and the Witten-Veneziano relation at finite temperature

We discuss and propose the minimal generalization of the Witten-Veneziano relation to finite temperatures, prompted by STAR and PHENIX experimental results on the multiplicity of eta' mesons. After explaining why these results show that the zero-temperature Witten-Veneziano relation cannot be straightforwardly extended to temperatures T too close to the chiral restoration temperature T_Ch and beyond, we find the quantity which should replace, at T>0, the Yang-Mills topological susceptibility appearing in the T=0 Witten-Veneziano relation, in order to avoid the conflict with experiment at T>0. This is illustrated through concrete T-dependences of pseudoscalar meson masses in a chirally well-behaved, Dyson-Schwinger approach, but our results and conclusions are of a more general nature and, essentially, model-independent.

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arXiv2011

Photon-neutrino interaction in theta-exact covariant noncommutative field theory

Photon-neutrino interactions arise quite naturally in noncommutative field theories. Such couplings are absent in ordinary field theory and imply experimental lower bounds on the energy scale Lambda_NC ~ 1/|theta|^2 of noncommutativity. Using non-perturbative methods and a Seiberg-Witten map based covariant approach to noncommutative gauge theory, we obtain theta-exact expressions for the interactions, thereby eliminating previous restrictions to low-energy phenomena. We discuss implications for plasmon decay, neutrino charge radii, big bang nucleosynthesis and ultrahigh energy cosmic rays. Our results behave reasonably throughout all interaction energy scales, thus facilitating further phenomenological applications.

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arXiv2011

Hunting up low-mass bosons from the Sun using HPGe detector

In this experiment we aim to look for keV-mass bosons emitted from the Sun, by looking at a process analogous to the photoelectric/Compton effect inside the HPGe detector. Their coupling to both electrons and nucleons is assumed. For masses above 25 keV, the mass dependence of our limit on the scalar-electron coupling reveals a constraint which proves stronger than that obtained recently and based on the very good agreement between the measured and predicted solar neutrino flux from the ^{8}B reaction. On the other hand, the mass dependence of our limit on the scalar-proton/electron coupling together entails a limit on a possible Yukawa addition to the gravitational inverse square low. Such a constraint on the Yukawa interactions proves much stronger than that derived from the latest AFM Casimir force measurement.

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arXiv2011

Spacetime noncommutativity and ultra-high energy cosmic ray experiments

If new physics were capable to push the neutrino-nucleon inelastic cross section three orders of magnitude beyond the standard-model (SM) prediction, then ultra-high energy (UHE) neutrinos would have already been observed at neutrino observatories. We use such a constraint to reveal information on the scale of noncommutativity (NC) Lambda_NC in noncommutative gauge field theories (NCGFT) where neutrinos possess a tree-level coupling to photons in a generation-independent manner. In the energy range of interest (10^10 to 10^11 GeV) the theta-expansion (|theta| ~ 1/Lambda_NC^2) and therefore the perturbative expansion in terms of Lambda_NC retains no longer its meaningful character, forcing us to resort to those NC field-theoretical frameworks involving the full theta-resummation. Our numerical analysis of the contribution to the process coming from the photon exchange, pins impeccably down a lower bound on Lambda_NC to be as high as around up to 900 (450) TeV, depending on the estimates for the cosmogenic neutrino flux. If, on the other hand, one considers a surprising recent result occurred in Pierre Auger Observatory (PAO) data, that UHE cosmic rays are mainly composed of highly-ionized Fe nuclei, then our bounds get weaker, due to the diminished cosmic neutrino flux. Nevertheless, we show that even for the very high fraction of heavy nuclei in primary UHE cosmic rays, our method may still yield remarkable bounds on Lambda_NC, typically always above 200 TeV. Albeit, in this case one encounters a maximal value for the Fe fraction from which any useful information on Lambda_NC can be drawn, delimiting thus the applicability of our method.

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arXiv2008

Search for solar hadronic axions produced by a bremsstrahlung-like process

We have searched for hadronic axions which may be produced in the Sun by a bremsstrahlung-like process, and observed in the HPGe detector by an axioelectric effect. A conservative upper limit on the hadronic axion mass m_a < 334 eV at 95% C.L. is obtained. Our experimental approach is based on the axion-electron coupling and it does not include the axion-nucleon coupling, which suffers from the large uncertainties related to the estimation of the flavor-singlet axial-vector matrix element.

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arXiv2008

Constraining theories of low-scale quantum gravity by non-observation of the bulk vector boson signal from the Sun

In this experiment we aim to detect Kaluza-Klein (KK) excitations of the bulk gauge field, emitted in a bremsstrahlung process on solar plasma constituents, by looking at a process analogous to the photoelectric effect inside the HPGe detector. Using a generic feature of the underlying effective theory that the unknown 4-dimensional gauge coupling is independent of the number of extra large dimensions delta, we show that the expected number of events in the detector is insensitive to the true scale of quantum gravity for delta=2. With the entire data collection time of 202 days in the energy interval 1.7 - 3.8 keV, the number of events detected was as low as 1.1x10^6, compared to 2.7x10^6 from the expected high multiplicity of the solar KK excitations for delta =2. Hence, our bound from the presumed existence of new forces associated with additional gauge bosons actually conforms with very stringent bounds set from various astrophysical considerations. Baring any modifications of the infrared part of the KK spectrum, this bound would therefore rule out the possibility of observing any signal at the LHC for delta=2. Although a dependence on the fundamental scale referring to 4+delta-dimensional gravity turns on again for delta=3, the experimental sensitivity of the present setup proves insufficient to draw any constraint for delta>2.

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arXiv2008

$η$ and $η'$ mesons in the Dyson-Schwinger approach using a generalization of the Witten-Veneziano relation

The description of the $η$ and $η^\prime$ mesons in the Dyson-Schwinger approach has relied on the Witten-Veneziano relation. The present paper explores the consequences of using instead its generalization recently proposed by Shore. On the examples of three different model interactions, we find that irrespective of the concrete model dynamics, our Dyson-Schwinger approach is phenomenologically more successful in conjunction with the standard Witten-Veneziano relation than with the proposed generalization valid in all orders in the $1/N_c$ expansion.

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arXiv2005

Circumventing the axial anomalies and the strong CP problem

Many meson processes are related to the U_A(1) axial anomaly, present in the Feynman graphs where fermion loops connect axial vertices with vector vertices. However, the coupling of pseudoscalar mesons to quarks does not have to be formulated via axial vertices. The pseudoscalar coupling is also possible, and this approach is especially natural on the level of the quark substructure of hadrons. In this paper we point out the advantages of calculating these processes using (instead of the anomalous graphs) the graphs where axial vertices are replaced by pseudoscalar vertices. We elaborate especially the case of the processes related to the Abelian axial anomaly of QED, but we speculate that it seems possible that effects of the non-Abelian axial anomaly of QCD can be accounted for in an analogous way.

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arXiv2005

Bypassing the axial anomalies

Many meson processes are related to the U_A(1) axial anomaly, present in the Feynman graphs where fermion loops connect axial vertices with vector vertices. However, the coupling of pseudoscalar mesons to quarks does not have to be formulated via axial vertices. The pseudoscalar coupling is also possible, and this approach is especially natural on the level of the quark substructure of hadrons. In this paper we point out the advantages of calculating these processes using (instead of the anomalous graphs) the Feynman graphs where axial vertices are replaced by pseudoscalar vertices. We elaborate especially the case of the processes related to the Abelian axial anomaly of QED, but we speculate that it seems possible that effects of the non-Abelian axial anomaly of QCD can be accounted for in an analogous way.

hep-ph↗

arXiv2005

eta and eta' mesons and dimension 2 gluon condensate

The study of light pseudoscalar quark-antiquark bound states in the Dyson-Schwinger approach with the effective QCD coupling enhanced by the interplay of the dimension 2 gluon condensate and dimension 4 gluon condensate , is extended to the eta-eta' complex. We include the effects of the gluon axial anomaly into the Dyson-Schwinger approach to mesons. The calculated masses, mixing and two-photon decay widths of eta and eta' mesons are in agreement with experiment. Also, in a model-independent way, we give the modification of the Gell-Mann--Okubo and Schwinger nonet relations due to the interplay of the gluon anomaly and SU(3) flavor symmetry breaking.

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arXiv2005

Chiral symmetry breaking via constituent quarks for qbarq pseudoscalar mesons

We base our chiral symmetry approach on the quark-level linear sigma model Lagrangian. Then we review the Nambu--Goldstone theorem with vanishing pi, K, eta_8 masses. Next we dynamically generate the pi, K, eta_8 masses away from the chiral limit. Then we study pion and kaon Goldberger-Treiman relations. Finally we extend this qbarq scheme to scalar and vector mesons. We also show the above qbarq meson scheme fits the higher mass octet baryon qqq pattern as well.

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arXiv2004

Search for hadronic axions using axioelectric effect

We made a search for hadronic axions which could be emitted from the Sun in M1 transitions between the first 14.4 keV thermally excited and the ground state in Fe-57, and absorbed in the HPGe detector by axioelectric effect. An upper limit on hadronic axion mass of 400 eV is obtained at the 95% confidence level.

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arXiv2000

Detection of weakly interacting light vector bosons by coherent scattering

We propose a novel experimental method to produce and detect weakly interacting light vector bosons using coherent processes in refractive media. A light vector boson would be produced by a laser photon scattered at a plane interface between two media of different dielectric properties and will be converted back to photon in the similar scattering process. The effect depends strongly on the indices of refraction of the two media. If incident and recovered photons were traveling through extremely high vacuums, limits on the existence of several light vector bosons could be substantially improved.

hep-ph↗

arXiv2000

Revisiting the U_A(1) problems

We survey various U_A(1) problems and attempt to resolve the two puzzles related to the eta mesons that have experimental verification. Specifically, we first explore the Goldstone structure of the eta and eta' mesons in the context of eta-eta' mixing using ideas based on QCD. Then we study the eta decays eta->3pi0, eta'->3pi0 and eta'->eta pi pi. Finally we arrive at essentially the same picture in the dynamical scheme based on consistently coupled Schwinger-Dyson and Bethe-Salpeter integral equations. This chirally well-behaved bound-state approach clarifies the distinction between the usual axial-current decay constants and the gamma gamma decay constants in the eta-eta' complex. Allowing for the effects of the SU(3) flavor symmetry breaking in the quark-antiquark annihilation, leads to the improved eta-eta' mass matrix.

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