Publications (55)165.18 Total impact

Article: Selfenergies on deformed spacetimes
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ABSTRACT: We study oneloop photon (Pi) and neutrino (Sigma) selfenergies in a U(1) covariant gaugetheory on ddimensional noncommutative spaces determined by a antisymmetricconstant tensor theta^{mu nu}. For the general fermionphoton (kappa_f) and photon selfinteraction (kappa_g) the closed form results reveal selfenergies besetting with all kind of pathological terms: the UV divergence, the quadratic UV/IR mixing terms as well as a logarithmic IR divergent term of the type ln(mu^2(theta p)^2). In addition, the photonloop produces new tensor structures satisfying transversality condition by themselves. We show that the photon selfenergy in fourdimensional Euclidean spacetime can be reduced to two finite terms by imposing a specific full rank of theta^{mu nu} and setting parameters (kappa_f,kappa_g)=(0,3). In this case the neutrino twopoint function vanishes. Thus for a specific point (0,3) in the parameterspace (kappa_f,kappa_g), a covariant thetaexact approach is able to produce a divergencefree result for oneloop quantum corrections, having also welldefined both the commutative limit as well as the pointlike limit of an extended object. While in twodimensional space the photon selfenergy is finite for arbitrary (kappa_f,kappa_g) combinations, the neutrino selfenergy still contains an superficial IR divergence.06/2013;  [Show abstract] [Hide abstract]
ABSTRACT: 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 photoelectriclike 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.Physics Letters B 10/2012; 721(s 4–5). · 4.57 Impact Factor 
Article: Forbidden and invisible Z boson decays in covariant thetaexact noncommutative standard model
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ABSTRACT: Triple neutral gauge boson and direct photonneutrino interactions arise quite naturally in noncommutative gauge field theories. Such couplings are absent in ordinary field theory and imply experimental lower bounds on the energy scale Lambda_NC ~ theta^{1/2} of spacetime noncommutativity. Using nonperturbative methods and a SeibergWitten (SW) map based covariant approach to noncommutative gauge theory, we obtain thetaexact expressions for the interactions, thereby eliminating previous restrictions to lowenergy phenomena. We discuss implications for Z > gamma gamma and Z > nu barnu decays, and show that our results behave reasonably throughout all interaction energy scales. Constraining the invisible Z width for this kind of new physics to be under around 1 MeV, one produces Lambda_NC ~ 140 GeV. Although with the current experimental upper limit on the branching ratio BR(Z > gamma gamma) the obtained bound on Lambda_NC is of the same order of magnitude, we have demonstrated how the expected improvement on the branching ratio from the LHC experiments may significantly strengthen the bound on the spacetime noncommutativity.Journal of Physics G Nuclear and Particle Physics 04/2012; · 5.33 Impact Factor 
Article: A bound on the scale of spacetime noncommutativity from the reheating phase after inflation
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ABSTRACT: In an approach to noncommutative gauge theories, where the full noncommutative behavior is delimited by the presence of the UV and IR cutoffs, we consider the possibility of describing a system at a temperature T in a box of size L. Employing a specific form of UV/IR relationship inherent in such an approach of restrictive noncommutativity, we derive, for a given temperature T, an upper bound on the parameter of spacetime noncommutativity Lambda_NC ~ theta^{1/2}. Considering such epochs in the very early universe which are expected to reflect spacetime noncommutativity to a quite degree, like the reheating stage after inflation, or believable preinflation radiationdominated epochs, the best limits on Lambda_NC are obtained. We also demonstrate how the nature and size of the thermal system (for instance, the Hubble distance versus the future event horizon) can affect our bounds.Physics Letters B 11/2011; 710(1). · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Oneloop thetaexact quantum corrections to the neutrino propagator are computed in noncommutative U*(1) gaugetheory based on SeibergWitten maps. Our closed form results show that the oneloop correction contains a hard 1/epsilon UV divergence, as well as a logarithmic IRdivergent term of the type ln sqrt(theta p)^2, thus considerably softening the usual UV/IR mixing phenomenon. We show that both of these problematic terms vanish for a certain choice of the noncommutative parameter theta which preserves unitarity. We find nonperturbative modifications of the neutrino dispersion relations which are assymptotically independent of the scale of noncommutativity in both the low and high energy limits and may allow superluminal propagation. Finally, we demonstrate how the prodigious freedom in SeibergWitten maps may be used to affect neutrino propagation in a profound way.Journal of High Energy Physics 11/2011; 2012(4). · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider Yukawa couplings in a thetaexact approach to noncommutative gauge field theory and show that both Dirac and singlet Majorana neutrino mass terms can be consistently accommodated. This shows that in fact the whole neutrinomass extended standard model on noncommutative spacetime can the formulated in the new nonperturbative (in theta) approach which eliminates the previous restriction of SeibergWitten map based theories to lowenergy phenomena. Spacetime noncommutativity induced couplings between neutrinos and photons as well as Zbosons appear quite naturally in the model. We derive relevant Feynman rules for the type I seesaw mechanism.Physics Letters B 09/2011; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In formulating gauge field theories on noncommutative (NC) spaces it is suggested that particles carrying gauge invariant quantities should not be viewed as pointlike, but rather as extended objects whose sizes grow linearly with their momenta. This and other generic properties deriving from the nonlocal character of interactions (showing thus unambiguously their quantumgravity origin) lead to a specific form of UV/IR mixing as well as to a pathological behavior at the quantum level when the noncommutativity parameter theta is set to be arbitrarily small. In spite of previous suggestions that in a NC gauge theory based on the thetaexpanded SeibergWitten (SW) maps UV/IR mixing effects may be under control, a fairly recent study of photon selfenergy within a SW thetaexact approach has shown that UV/IR mixing is still present. We study the selfenergy contribution for neutral fermions in the thetaexact approach of NC QED, and show by explicit calculation that all but one divergence can be eliminated for a generic choice of the noncommutativity parameter theta. The remaining divergence is linked to the pointlike limit of an extended object.Journal of High Energy Physics 09/2011; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Photonneutrino 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 nonperturbative methods and a SeibergWitten map based covariant approach to noncommutative gauge theory, we obtain thetaexact expressions for the interactions, thereby eliminating previous restrictions to lowenergy 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.Physical review D: Particles and fields 03/2011; 84.  [Show abstract] [Hide abstract]
ABSTRACT: In this experiment we aim to look for keVmass 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 scalarelectron 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 8B reaction. On the other hand, the mass dependence of our limit on the scalarproton/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.Physics Letters B 01/2011; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In a recently proposed scenario for primordial inflation, where the Standard Model (SM) Higgs boson plays a role of the inflation field, an effective field theory (EFT) approach is the most convenient for working out the consequences of breaking of perturbative unitarity, caused by the strong coupling of the Higgs field to the Ricci scalar. The domain of validity of the EFT approach is given by the ultraviolet (UV) cutoff, which, roughly speaking, should always exceed the Hubble parameter in the course of inflation. On the other hand, applying the trusted principles of quantum gravity to a local EFT demands that it should only be used to describe states in a region larger than their corresponding Schwarschild radius, manifesting thus a sort of UV/IR correspondence. We consider both constraints on EFT, to ascertain which models of the SM Higgs inflation are able to simultaneously comply with them. We also show that if the gravitational coupling evolves with the scale factor, the holographic constraint can be alleviated significantly with minimal set of canonical assumptions, by forcing the said coupling to be asymptotically free.Physics Letters B 01/2011; 699(3). · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: If new physics were capable of pushing the neutrinonucleon inelastic cross section 3 orders of magnitude beyond the standard model prediction, then ultrahigh 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) ΛNC in noncommutative gauge field theories where neutrinos possess a treelevel coupling to photons in a generationindependent manner. In the energy range of interest (1010 to 1011 GeV), the θ expansion (θ∼1/ΛNC2) and, therefore, the perturbative expansion, in terms of ΛNC, retains no longer its meaningful character, forcing us to resort to those NC field theoretical frameworks involving the full θ resummation. Our numerical analysis of the contribution to the process coming from the photon exchange impeccably pins down a lower bound on ΛNC to be as high as 900 (450) TeV, depending on the estimates for the cosmogenic neutrino flux. If, on the other hand, one considers a surprising recent result that occurred in Pierre Auger Observatory 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 ΛNC, typically always above 200 TeV. Albeit, in this case, one encounters a maximal value for the Fe fraction, from which any useful information on ΛNC can be drawn, delimiting thus the applicability of our method.Physical review D: Particles and fields 05/2010; 83(6).  [Show abstract] [Hide abstract]
ABSTRACT: We study a process of equilibration of holographic dark energy (HDE) with the cosmic horizon around the darkenergy dominated epoch. This process is characterized by a huge amount of information conveyed across the horizon, filling thereby a large gap in entropy between the system on the brink of experiencing a sudden collapse to a black hole and the black hole itself. At the same time, even in the absence of interaction between dark matter and dark energy, such a process marks a strong jump in the entanglement entropy, measuring the quantummechanical correlations between the horizon and its interior. Although the effective quantum field theory (QFT) with a peculiar relationship between the UV and IR cutoffs, a framework underlying all HDE models, may formally account for such a huge shift in the number of distinct quantum states, we show that the scope of such a framework becomes tremendously restricted, devoiding it virtually any application in other cosmological epochs or particlephysics phenomena. The problem of negative entropies for the nonphantom stuff is also discussed. Comment: 10 pages, version to appear in PLBPhysics Letters B 03/2010; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Effective field theories that manifest UV/IR mode mixing in such a way as to be valid for arbitrarily large volumes, can be used for gravitational, nonblack hole events to be accounted for. In formulating such theories with a large number of particle species $N$, we employ constraints from the muon $g2$, higherdimensional operator corrections due to the required UV and IR cutoffs as well as the RG evolution in a conventional fieldtheoretical model in curved space. While in general our bounds on $N$ do reflect $N \simeq 10^{32}$, a bound motivated by the solution to the hierarchy problem in alike theories and obtained by the fact that strong gravity has not been seen in the particle collisions, the bound from the muon $g2$ turns out to be much stronger, $N \lsim 10^{19}$. For systems on the verge of gravitational collapse, this bound on $N$ is far too restrictive to allow populating a large gap in entropy between those systems and that of black holes of the same size. Comment: 7 pages, version to appear in JHEPJournal of High Energy Physics 11/2009; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We discuss a constraint on the scale $\Lambda_{\rm NC}$ of noncommutative (NC) gauge field theory arising from consideration of the big bang nucleosynthesis (BBN) of light elements. The propagation of neutrinos in the NC background described by an antisymmetric tensor $\theta^{\mu\nu}$ does result in a treelevel vectorlike coupling to photons in a generationindependent manner, raising thus a possibility to have an appreciable contribution of three light righthanded (RH) fields to the energy density of the universe at nucleosynthesis time. Considering elastic scattering processes of the RH neutrinos off charged plasma constituents at a given cosmological epoch, we obtain for a conservative limit on an effective number of additional doublet neutrinos, $\Delta N_\nu =1$, a bound $\Lambda_{\rm NC} \stackrel{>}{\sim}$ 3 TeV. With a more stringent requirement, $\Delta N_\nu \lesssim 0.2$, the bound is considerably improved, $\Lambda_{\rm NC} \stackrel{>}{\sim} 10^3$ TeV. For our bounds the $\theta$expansion of the NC action stays always meaningful, since the decoupling temperature of the RH species is perseveringly much less than the inferred bound for the scale of noncommutativity. Comment: 4 pages, version to appear in PRDPhysical review D: Particles and fields 01/2009;  [Show abstract] [Hide abstract]
ABSTRACT: In this Letter we discuss light neutrino dipole moments, computed in the neutrinomass extended Standard Model, as a possible source for neutrino condensates which may cause cosmological constant observed today.Physics Letters B 01/2009; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: An effective quantum field theory (QFT) with a manifest UV/IR connection, so as to be valid for arbitrarily large volumes, can successfully be applied to the cosmological dark energy problem as well as the cosmological constant (CC) problem. Motivated by recent approaches to the hierarchy problem, we develop such a framework with a large number of particle species. When applying to systems on the brink of experiencing a sudden collapse to a black hole, we find that the entropy, unlike the total energy, now becomes an increasing function of the number of field species. An internal consistency of the theory is then used to infer the upper bound on the number of particle species, showing consistency with the holographic Bekenstein–Hawking bound. This may thus serve to fill in a large gap in entropy of any nonblack hole configuration of matter and the black holes. In addition, when the bound is saturated the entanglement entropy matches the black hole entropy, thus solving the multiplicity of species problem. In a cosmological setting, the maximum allowable number of species becomes a function of cosmological time, reaching its minimal value in a lowentropy postreheating epoch.Physics Letters B 01/2009; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Holographic dark energy (HDE) models, underlain by an effective quantum field theory (QFT) with a manifest UV/IR connection, have become a convincing candidate for the dark energy in the universe. On the other hand, the maximum number of quantum states a conventional QFT in the box of size $L$ is capable to describe, refer to those boxes which are on the brink of experiencing a sudden collapse to a black hole. Another restriction on the underlying QFT is that the UV cutoff, which cannot be chosen independently of the IR cutoff and therefore becomes a function of time in a cosmological setting, should stay the largest energy scale even in the standard cosmological epochs preceding a dark energy dominated one. We show that, irrespective of whether one deals with the saturated form of HDE or takes a certain degree of nonsaturation in the past, the above restrictions cannot be met in a radiationdominated universe, an epoch in the history of the universe which is expected to be perfectly describable within conventional QFT.Journal of Cosmology and Astroparticle Physics 07/2008; · 6.04 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In this experiment we aim to detect KaluzaKlein (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 4dimensional 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+deltadimensional gravity turns on again for delta=3, the experimental sensitivity of the present setup proves insufficient to draw any constraint for delta>2.Physical review D: Particles and fields 05/2008;  [Show abstract] [Hide abstract]
ABSTRACT: Classical and quantum entropic properties of holographic dark energy (HDE) are considered in view of the fact that its entropy is far more restrictive than the entropy of a black hole of the same size. In cosmological settings (in which HDE is promoted to a plausible candidate for being the dark energy of the universe), HDE should be viewed as a combined state composed of the event horizon and the stuff inside the horizon. By any interaction of the subsystems, the horizon and the interior become entangled, raising thereby a possibility that their quantum correlations be responsible for the almost purity of the combined state. Under this circumstances, the entanglement entropy is almost the same for both subsystems, being also of the same order as the thermal (coarse grained) entropy of the interior or the horizon. In the context of thermodynamics, however, only additive coarse grained entropies matter, so we use these entropies to test the generalized second law (GSL) of gravitational thermodynamics in this framework. While we find that the original Li's model passes the GSL test for a special choice of parameters, in a saturated model with the choice for the IR cutoff in the form of the Hubble parameter, the GSL always breaks down.Physics Letters B 01/2008; · 4.57 Impact Factor 
Chapter: Axions and Large Extra Dimensions
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ABSTRACT: Theories including extra space dimensions offer a possible solution to the hierarchy problem of particle physics. An additional effect of these theories is the possibility for axions to propagate in the higherdimensional space. We explore the potential of the CERN Axion Solar Telescope (CAST) for testing the presence of large extra dimensions.10/2007: pages 7382;
Publication Stats
706  Citations  
165.18  Total Impact Points  
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Institutions

1984–2012

Ruđer Bošković Institute
 Division of Experimental Physics
Zagrabia, Grad Zagreb, Croatia


2009

Institute of Physics, Zagreb
Zagrabia, Grad Zagreb, Croatia


1988

University of Ottawa
 Department of Physics
Ottawa, Ontario, Canada
