Showing papers in "Modern Physics Letters A in 2013"
TL;DR: In this paper, it was shown that the solution of a self-interacting Pais-Uhlenbeck (PU) oscillator is stable on islands in the parameter space, as already observed in the literature.
Abstract: It is shown that the interacting Pais–Uhlenbeck (PU) oscillator necessarily leads to a description with a Hamiltonian that contains positive and negative energies associated with two oscillators. Descriptions with a positive definite Hamiltonians, considered by some authors, can hold only for a free PU oscillator. We demonstrate that the solutions of a self-interacting PU oscillator are stable on islands in the parameter space, as already observed in the literature. If we slightly modify the system, by considering a sine interaction term, and/or by taking unequal masses of the two oscillators, then the system is stable on the continents that extend from zero to infinity in the parameter space. Therefore, the PU oscillator is quite acceptable physical system.
77 citations
TL;DR: The LHeC is the cleanest microscope of parton dynamics and a precision Higgs facility in the world as mentioned in this paper, and its further development with emphasis on its role as a cleanest microscopy.
Abstract: An overview is given on key physics, detector and accelerator aspects of the LHeC including its further development with emphasis to its role as the cleanest microscope of parton dynamics and a precision Higgs facility.
76 citations
TL;DR: In this article, the authors present a concise discussion of the most popular phenomenological interpretation of such findings, based on a hypothetical flavor conversion phenomenon of the ordinary "active" neutrinos into new light "sterile" species having mass $m \sim \mathcal{O}(1),\,\,{\rm eV}
Abstract: An increasing number of anomalous experimental results are emerging, which cannot be described within the standard three-neutrino framework. We present a concise discussion of the most popular phenomenological interpretation of such findings, based on a hypothetical flavor conversion phenomenon of the ordinary "active" neutrinos into new light "sterile" species having mass $m \sim \mathcal{O}(1)\,\,{\rm eV}$.
75 citations
TL;DR: The current status of flavored dark matter (DM) is reviewed in this paper, where the main experimental constraints on models of flavored DM are discussed and some possible considerations which are relevant for the constructions of models.
Abstract: The current status of flavored dark matter (DM) is reviewed. We discuss the main experimental constraints on models of flavored DM and survey some possible considerations which are relevant for the constructions of models. We then review the application of existing flavor principles to DM, with an emphasis on minimal flavor violation, and discuss implications of flavored DM on collider phenomenology.
60 citations
TL;DR: In this paper, it is shown that it is possible to unambiguously determine the leading color-octet (CO) long-distance matrix elements (LDMEs) in compliance with the velocity scaling rules through a global fit to experimental data of unpolarized J/ψ production in pp,, ep, ep, γγ, and e+e collisions.
Abstract: We report on recent progress in testing the factorization formalism of non-relativistic quantum chromodynamics (NRQCD) at next-to-leading order (NLO) for J/ψ yield and polarization We demonstrate that it is possible to unambiguously determine the leading color-octet (CO) long-distance matrix elements (LDMEs) in compliance with the velocity scaling rules through a global fit to experimental data of unpolarized J/ψ production in pp, , ep, γγ, and e+e- collisions Three data sets not included in the fit, from hadro-production and from photo-production in the fixed-target and colliding-beam modes, are nicely reproduced The polarization observables measured in different frames at DESY HERA and CERN LHC reasonably agree with NLO NRQCD predictions obtained using the LDMEs extracted from the global fit, while measurements at the FNAL Tevatron exhibit severe disagreement We demonstrate that the alternative LDME sets recently obtained, with different philosophies, in two other NLO NRQCD analyses of J/ψ yield and polarization also fail to reconcile the Tevatron polarization data with the other available world data
58 citations
TL;DR: In this paper, the authors studied the Godel universe in the framework of f(R, T) modified theories of gravity, where R is the curvature scalar and T the trace of the energy-momentum tensor.
Abstract: In this paper, we study Godel universe in the framework of f(R, T) modified theories of gravity, where R is the curvature scalar and T the trace of the energy–momentum tensor. We demonstrate that Godel solution occurs in this modified theory and still we suggest a path to understanding the smallness of the cosmological constant.
55 citations
TL;DR: In this article, it was shown that a cosmological model is compatible with a constant jerk, here conventionally rewritten as j = 1+ϵ, with ϵ > 0 representing a departure from the ΛCDM model.
Abstract: In this paper, we demonstrate that the variation of acceleration, namely the jerk parameter j, could give hints for determining the dark energy equation of state (EoS). In particular, it is possible to show that a viable cosmological model is compatible with a constant jerk, here conventionally rewritten as j = 1+ϵ, with ϵ > 0 representing a departure from the ΛCDM model. This suggests that the cosmological constant could be seen as a limiting case of a more general dark energy model. We use the most recent union 2.1 compilation of supernovae Ia, showing at 1σ confidence level, that j is compatible with the condition j ≥ 1. In doing so, we infer a corresponding cosmological model, viable with a negative acceleration parameter, in the observed range -1 < q0 < 0.
49 citations
TL;DR: An overview of the state-of-the-art of the MPGD technologies and summarizes ongoing activities within the framework of the RD51 collaboration can be found in this article, where the authors present a review of the current state of the art.
Abstract: Discoveries in particle physics vitally depend on parallel advances in radiation-detector technologies. A true innovation in detector instrumentation concepts came in 1968, with the development of a fully parallel readout for a large array of sensing elements — the Multi-Wire Proportional Chamber (MWPC), which earned Georges Charpak a Nobel Prize in Physics in 1992. This invention revolutionized particle detection which moved from optical-readout devices (cloud chamber, emulsion or bubble chambers) to the electronics era. Over the past two decades advances in photo-lithography, microelectronics and printed-circuit board (PCB) techniques triggered a major transition in the field of gas detectors from wire structures to the Micro-Pattern Gas Detector (MPGD) concepts. The excellent spatial and time resolution, high rate capability, low mass, large active areas, and radiation hardness make them an invaluable tool to confront future detector challenges at the frontiers of research. The design of the new micro-pattern devices appears suitable for industrial production. Novel devices where MPGDs are directly coupled to the CMOS pixel readout serve as an "electronic bubble chamber" allowing to record space points and tracks in 3D. In 2008, the RD51 collaboration at CERN has been established to further advance technological developments of MPGDs and associated electronic-readout systems, for applications in basic and applied research. This review provides an overview of the state-of-the-art of the MPGD technologies and summarizes ongoing activities within the framework of the RD51 collaboration.
47 citations
TL;DR: In this article, the authors conjecture that weak interactions are peculiar manifestations of quantum gravity at the Fermi scale, and that the fermi constant is related to the Newtonian constant of gravitation.
Abstract: We conjecture that weak interactions are peculiar manifestations of quantum gravity at the Fermi scale, and that the Fermi constant is related to the Newtonian constant of gravitation. In this framework one may understand the violations of fundamental symmetries by the weak interactions, in particular parity violations, as due to fluctuations of the spacetime geometry at a Planck scale coinciding with the Fermi scale. As a consequence, gravitational phenomena should play a more important role in the microworld, and experimental settings are suggested to test this hypothesis.
47 citations
TL;DR: In this article, the BRST and anti-BRST symmetries for perturbative quantum gravity in noncommutative spacetime were discussed and the violation of unitarity was analyzed.
Abstract: We discuss the BRST and anti-BRST symmetries for perturbative quantum gravity in noncommutative spacetime. In this noncommutative perturbative quantum gravity the sum of the classical Lagrangian density with a gauge fixing term and a ghost term is shown to be invariant to the noncommutative BRST and the noncommutative anti-BRST transformations. We analyze the gauge fixing term and the ghost term in both linear as well as nonlinear gauges. We also discuss the unitarity evolution of the theory and analyze the violation of unitarity by introduction of a bare mass term in the noncommutative BRST and the noncommutative anti-BRST transformations.
44 citations
TL;DR: In this article, the authors review the theoretical and lattice evidence for violation of positivity as well as various interpretations of this violation, and consider methods for checking superconvergence on the lattice (so far undone).
Abstract: Both lattice simulations and theoretical studies show that the spectral function of the gluon propagator of QCD (in various gauges, as well as for the gauge-invariant Pinch Technique, or PT, propagator) is not nonnegative everywhere, although it should be if it has a physical interpretation as in QED. Theory says moreover that the non-positive spectral function of the Landau-gauge or of the PT gluon propagator is further constrained to obey a superconvergence relation (the integral of the spectral function vanishes). We review the theoretical and lattice evidence for violation of positivity as well as various interpretations of this violation, and consider methods for checking superconvergence on the lattice (so far undone). The most common interpretation is that positivity violation implies confinement of gluons, so the gluon propagator does not describe processes with physical gluons. Another more direct and gauge-invariant interpretation arises from the PT: Asymptotic freedom alone demands non-positivity and superconvergence.
TL;DR: In this paper, the authors review a growing theoretical motivation and evidence that the number of dimensions actually reduces at high energies, which can happen near the Planck scale, or much before, the dimensions that are reduced can be effective, spectral, topological or the usual dimensions.
Abstract: We review a growing theoretical motivation and evidence that the number of dimensions actually reduces at high energies. This reduction can happen near the Planck scale, or much before, the dimensions that are reduced can be effective, spectral, topological or the usual dimensions, but many things point toward the fact that the high energy theories appear to propagate in a lower-dimensional space, rather than a higher-dimensional one. We will concentrate on a particular scenario of "vanishing" or "evolving dimensions" where the dimensions open up as we increase the length scale that we are probing, but will also mention related models that point to the same direction, i.e. the causal dynamical triangulation, asymptotic safety, as well as evidence coming from a noncommutative quantum theories, the Wheeler–DeWitt equation and phenomenon of "asymptotic silence". It is intriguing that experimental evidence for the high energy dimensional reduction may already exist — a statistically significant planar alignment of events with energies higher than TeV has been observed in high altitude cosmic ray experiments. A convincing evidence for dimensional reduction may be found in future in collider experiments and gravity waves observatories.
TL;DR: In this article, the authors review the results from the RHIC beam energy scan (BES) program, aimed at studying the Quantum Chromodynamics (QCD) phase diagram, where the main goals are to search for the possible phase boundary, softening of equation of state or first order phase transition, and possible critical point.
Abstract: We review recent results from the RHIC beam energy scan (BES) program, aimed to study the Quantum Chromodynamics (QCD) phase diagram. The main goals are to search for the possible phase boundary, softening of equation of state or first order phase transition, and possible critical point. Phase-I of the BES program has recently concluded with data collection for Au+Au collisions at center-of-mass energies of 7.7, 11.5, 19.6, 27 and 39 GeV. Several interesting results are observed for these lower energies where the net-baryon density is high at the mid-rapidity. These results indicate that the matter formed at lower energies (7.7 and 11.5 GeV) is hadron dominated and might not have undergone a phase transition. In addition, a centrality dependence of freeze-out parameters is observed for the first time at lower energies, slope of directed flow for (net)-protons measured versus rapidity shows an interesting behavior at lower energies, and higher moments of net-proton show deviation from Skellam expectations at lower energies. An outlook for the future BES Phase-II program is presented and efforts for the detailed study of QCD phase diagram are discussed.
TL;DR: In this paper, a brief review of the electroweak vacuum stability and related theoretical issues in the Standard Model is given, and possible ways to save the stability are also discussed. But, if there is no new physics between electroweak and Planck scale, we then do not have a stable vacuum.
Abstract: The long-awaited Higgs particle H around 125 GeV has been observed at the LHC. Interpreting it as the Standard Model Higgs boson and if there is no new physics between electroweak and Planck scale, we then do not have a stable vacuum. Here, we give a brief review of the electroweak vacuum stability and some related theoretical issues in the Standard Model. Possible ways to save the stability are also discussed.
TL;DR: In this paper, the thermodynamic and spectroscopic properties of Schwarzschild black hole surrounded by quintessence are studied and the authors derived the thermodynamics quantities and studied their behavior for different values of quintessense parameter.
Abstract: The thermodynamic and spectroscopic behavior of Schwarzschild black hole surrounded by quintessence are studied. We have derived the thermodynamic quantities and studied their behavior for different values of quintessence parameter. We put the background spacetime into the Kruskal-like coordinate to find the period with respect to Euclidean time. Also assuming that the adiabatic invariant obeys Bohr–Sommerfeld quantization rule, detailed study of area spectrum and entropy spectrum have been done for special cases of the quintessence state parameter. We find that the spectra are equally spaced.
TL;DR: In this article, the duality symmetry between the electric and the magnetic fields was extended to the case of an additional axion-like term, and the set of Maxwell equations that preserved this symmetry was derived.
Abstract: We extend the duality symmetry between the electric and the magnetic fields to the case in which an additional axion-like term is present, and we derive the set of Maxwell equations that preserves this symmetry. This new set of equations allows for a gauge symmetry extending the ordinary symmetry in the classical electrodynamics. We obtain explicit solutions for the new set of equations in the absence of external sources, and we discuss the implications of a new internal symmetry between the axion field and the electromagnetic gauge potential.
TL;DR: In this article, the scalar perturbations of the charged dilaton black hole (CDBH) were employed to obtain the quantum entropy and area spectra of these black holes.
Abstract: In this study, we employ the scalar perturbations of the charged dilaton black hole (CDBH) found by Chan, Horne and Mann (CHM), and described with an action which emerges in the low-energy limit of the string theory. A CDBH is neither asymptotically flat (AF) nor non-asymptotically flat (NAF) spacetime. Depending on the value of its dilaton parameter a, it has both Schwarzschild and linear dilaton black hole (LDBH) limits. We compute the complex frequencies of the quasinormal modes (QNMs) of the CDBH by considering small perturbations around its horizon. By using the highly damped QNM in the process prescribed by Maggiore, we obtain the quantum entropy and area spectra of these black holes (BHs). Although the QNM frequencies are tuned by a, we show that the quantum spectra do not depend on a, and they are equally spaced. On the other hand, the obtained value of undetermined dimensionless constant ϵ is the double of Bekenstein's result. The possible reason of this discrepancy is also discussed.
TL;DR: In this article, the authors deduced a general formula for pressure of degenerate and relativistic electrons, P-e, which is suitable for superhigh magnetic fields, and discussed the quantization of Landau levels of electrons, and considered the quantum electrodynamic (QED) effects on the equations of states (EOSs) for different matter systems.
Abstract: Based on our previous work, we deduce a general formula for pressure of degenerate and relativistic electrons, P-e, which is suitable for superhigh magnetic fields, discuss the quantization of Landau levels of electrons, and consider the quantum electrodynamic (QED) effects on the equations of states (EOSs) for different matter systems. The main conclusions are as follows: P-e is related to the magnetic field B, matter density rho, and electron fraction Y-e; the stronger the magnetic field, the higher the electron pressure becomes; the high electron pressure could be caused by high Fermi energy of electrons in a superhigh magnetic field; compared with a common radio pulsar, a magnetar could be a more compact oblate spheroid-like deformed neutron star (NS) due to the anisotropic total pressure; and an increase in the maximum mass of a magnetar is expected because of the positive contribution of the magnetic field energy to the EOS of the star.
TL;DR: In this paper, a uniform inverse correlation between phase-space and the square of the nuclear matrix element was found for 0νββ decay, and no isotope is either favored or disfavored; all have qualitatively the same decay rate per unit mass for any given value of the Majorana mass.
Abstract: Neutrinoless double beta decay has been the subject of intensive theoretical work as it represents the only practical approach to discovering whether neutrinos are Majorana particles or not, and whether lepton number is a conserved quantum number. Available calculations of matrix elements and phase-space factors are reviewed from the perspective of a future large-scale experimental search for 0νββ decay. Somewhat unexpectedly, a uniform inverse correlation between phase-space and the square of the nuclear matrix element emerges. As a consequence, no isotope is either favored or disfavored; all have qualitatively the same decay rate per unit mass for any given value of the Majorana mass.
CERN1
TL;DR: In this paper, the authors report on the Muon ATLAS MicroMegas Activity (MAMMA) R&D project aimed at the construction of large-area spark-resistant muon chambers using the micromegas technology.
Abstract: The upgrade of the ATLAS detector at the Large Hadron Collider (LHC) at CERN calls for a new generation of muon detectors capable of operating in a flux of collision and background particles approximately ten times larger compared to today's conditions We report here on the Muon ATLAS MicroMegas Activity (MAMMA) R&D project aimed at the construction of large-area spark-resistant muon chambers using the micromegas technology
TL;DR: In this article, the properties of Schwarzschild black hole surrounded by quintessence matter were studied and the existence of Nariai type black hole for special values of the parameters in the theory was shown.
Abstract: In this paper we study the properties of Schwarzschild black hole surrounded by quintessence matter. The main objective of the paper is to show the existence of Nariai type black hole for special values of the parameters in the theory. The Nariai black hole with the quintessence has the topology dS2 ×S2 with dS2 with a different curvature than what would be expected for the Schwarzschild–de Sitter degenerate black hole. Temperature and the entropy for the Schwarzschild–de Sitter black hole and the Schwarzschild-quintessence black hole are compared. The temperature and the curvature are computed for general values of the state parameter ω.
TL;DR: The zero width approximation (ZWA) as discussed by the authors restricts the intermediate unstable particle state to the mass shell and, when combined with the decorrelation approximation, fully factorizes the production and decay of unstable particles.
Abstract: The zero-width approximation (ZWA) restricts the intermediate unstable particle state to the mass shell and, when combined with the decorrelation approximation, fully factorizes the production and decay of unstable particles. The ZWA uncertainty is expected to be of , where M and Γ are the mass and width of the unstable particle. We review the ZWA and demonstrate that errors can be much larger than expected if a significant modification of the Breit–Wigner lineshape occurs. A thorough examination of the recently discovered candidate Standard Model Higgs boson is in progress. For MH≈125 GeV, one has ΓH/MH 2MV, where also sizable Higgs-continuum interference occurs. We discuss how experimental selection cuts can be used to suppress this region in search channels where the Higgs mass cannot be reconstructed. We note that H→VV decay modes in non-gluon-fusion channels are similarly affected.
TL;DR: In this article, it has been argued that there should be a duality between bound states and the elementary particles in this sector, at least in leading order in an expansion in the Higgs quantum fluctuations around its expectation value.
Abstract: Though being weakly interacting, QED can support bound states. In principle, this can be expected for the weak interactions in the Higgs sector as well. In fact, it has been argued long ago that there should be a duality between bound states and the elementary particles in this sector, at least in leading order in an expansion in the Higgs quantum fluctuations around its expectation value. Whether this remains true beyond the leading order is being investigated using lattice simulations, and support is found. This provides a natural interpretation of peaks in cross-sections as bound states. This would imply that (possibly very broad) resonances of Higgs and W and Z bound states could exist within the Standard Model.
TL;DR: In this article, the same-sign-dilepton (SSD) signal can be observed at the LHC with a lifetime of about 1025 years if the heavy neutrino mass is 3.3 TeV.
Abstract: The vacuum stability condition of the Standard Model (SM) Higgs potential with mass in the range of 124–127 GeV puts an upper bound on the Dirac mass of the neutrinos. We study this constraint with the right-handed neutrino masses up to TeV scale. The heavy neutrinos contribute to ΔL = 2 processes like neutrinoless double beta decay and same-sign-dilepton (SSD) production in the colliders. The vacuum stability criterion also restricts the light-heavy neutrino mixing and constrains the branching ratio (BR) of lepton flavor-violating process, like μ→eγ mediated by the heavy neutrinos. We show that neutrinoless double beta decay with a lifetime ~1025 years can be observed if the lightest heavy neutrino mass is 3.3 TeV. Finally we show that the observation of SSDs associated with jets at the LHC needs much larger luminosity than available at present. We have estimated the possible maximum cross-section for this process at the LHC and show that with an integrated luminosity 100 fb-1 it may be possible to observe the SSD signals as long as MR < 400 GeV.
TL;DR: In this paper, the relation between the value of θ23 in nature and the mixing angle measured in νμ disappearance experiments is analyzed analytically, and it is shown that not using the correct relation in calculating oscillation probabilities can result in a wrong best-fit value for θ 23, and spurious sensitivity to the octant of the two octants.
Abstract: The moderately large measured value of θ13 signals a departure from the approximate two-flavor oscillation framework. As a consequence, the relation between the value of θ23 in nature, and the mixing angle measured in νμ disappearance experiments is nontrivial. In this paper, we calculate this relation analytically. We also derive the correct conversion between degenerate values of θ23 in the two octants. Through simulations of a νμ disappearance experiment, we show that there are observable consequences of not using the correct relation in calculating oscillation probabilities. These include a wrong best-fit value for θ23, and spurious sensitivity to the octant of θ23.
TL;DR: In this article, the authors considered different dark energy (DE) models along with a time-dependent viscous model to construct the viscous equation of state (EoS) parameter for these DE models.
Abstract: We study the bulk viscosity taking dust matter in the generalized teleparallel gravity. We consider different dark energy (DE) models in this scenario along with a time-dependent viscous model to construct the viscous equation of state (EoS) parameter for these DE models. We discuss the graphical representation of this parameter to investigate the viscosity effects on the accelerating expansion of the universe. It is mentioned here that the behavior of the universe depends upon the viscous coefficients showing the transition from decelerating to accelerating phase. It leads to the crossing of phantom divide line and becomes phantom dominated for specific ranges of these coefficients.
TL;DR: The Generalized Uncertainty Principle (GOP) as discussed by the authors suggests corrections to the uncertainty principle as the energy increases towards the Planck value, leading to the concept of a Generalized Event Horizon.
Abstract: We propose a new way in which black holes connect macrophysics and microphysics. The Generalized Uncertainty Principle suggests corrections to the Uncertainty Principle as the energy increases towards the Planck value. It also provides a natural transition between the expressions for the Compton wavelength below the Planck mass and the black hole event horizon size above it. This suggests corrections to the event horizon size as the black hole mass falls towards the Planck value, leading to the concept of a Generalized Event Horizon. Extrapolating this expression below the Planck mass suggests the existence of a new kind of black hole, whose size is of order its Compton wavelength. Recently it has been found that such a black hole solution is permitted by loop quantum gravity, its unusual properties deriving from the fact that it is hidden behind the throat of a wormhole. This has important implications for the formation and evaporation of black holes in the early Universe, especially if there are extra spatial dimensions.
TL;DR: Chimento, Luis Pascual as mentioned in this paper, et al. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires, Argentina.
Abstract: Fil: Chimento, Luis Pascual. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina
TL;DR: In this paper, a (4+n)-dimensional theory is incorporated with modified gravity, which accounts for the discrepancy between spectroscopic results from muonic and electronic hydrogen experiments, and the puzzle can be solved with stringent constraint on the range of the new force.
Abstract: We propose a theoretical scenario to solve the proton radius puzzle which recently arises from the muonic hydrogen experiment. In this framework, (4+n)-dimensional theory is incorporated with modified gravity. The extra gravitational interaction between the proton and muon at very short range provides an energy shift which accounts for the discrepancy between spectroscopic results from muonic and electronic hydrogen experiments. Assuming the modified gravity is a small perturbation to the existing electromagnetic interaction, we find the puzzle can be solved with stringent constraint on the range of the new force. Our result not only provides a possible solution to the proton radius puzzle but also suggests a direction to test new physics at very small length scale.
TL;DR: In this article, the modifications induced by spacetime anisotropy on the Casimir effect in the case of two parallel plates were studied and non-perturbative and perturbative regimes were analyzed.
Abstract: We study the modifications induced by spacetime anisotropy on the Casimir effect in the case of two parallel plates. Non-perturbative and perturbative regimes are analyzed. In the first case, the Casimir force either vanishes or it reverses its direction which, in any case, makes the proposal untenable. On the other hand, the perturbative model enables us to incorporate appropriately the effects of spacetime anisotropy.