Scholarly Works, Physics

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Research articles, presentations, and other scholarship

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Browsing Scholarly Works, Physics by Department "Institute for Particle, Nuclear and Astronomical Sciences (IPNAS)"

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    14-year program monitoring the flux densities of 33 radio sources at low frequencies
    Salgado, José Francisco; Altschuler, Daniel R.; Ghosh, Tapasi; Dennison, Brian K.; Mitchell, Kenneth J.; Payne, Harry E. (IOP PUBLISHING LTD, 1999-01)
    We present the results of a low-frequency flux density monitoring program of 33 extragalactic radio sources. The light curves at 318 and 430 MHz over a 14 yr period are presented. The measurements were made with the NAIC Arecibo 305 m radio telescope at approximately bimonthly intervals between 1980 January and 1989 February and at less regular intervals between 1989 October and 1993 October, for a total of 64 observing sessions. In addition, we provide a first discussion of the results, pointing out several source properties and interesting objects.
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    An analysis of nonoblique corrections to the Zb¯b vertex
    Takeuchi, Tatsu; Grant, Aaron K.; Rosner, Jonathan L. (1994)
    We present a model–independent analysis of the Zb¯b vertex, with the aim of constraining contributions of new physics to the left- and right–handed couplings of the b. We find that the left–handed coupling of the b is quite narrowly constrained by present data, but that the right–handed coupling is still largely unconstrained.
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    Background independent quantum mechanics and gravity
    Minic, Djordje; Tze, C. H. (American Physical Society, 2003-09-15)
    We argue that the demand of background independence in a quantum theory of gravity calls for an extension of standard geometric quantum mechanics. We discuss a possible kinematical and dynamical generalization of the latter by way of a quantum covariance of the state space. Specifically, we apply our scheme to the problem of a background independent formulation of matrix theory.
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    Charge assignments in multiple-U(1) gauge theories
    Loinaz, William; Takeuchi, Tatsu (American Physical Society, 1999-12-01)
    We discuss the choice of gauge field basis in multiple-U(1) gauge theories. We find that there is a preferred basis, specified by the charge orthogonality condition, in which the U(1) gauge fields do not mix under one-loop renormalization group running. [S0556-2821(99)04219-8].
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    Constraining new physics with vertex corrections
    Takeuchi, Tatsu; Lebedev, O.; Loinaz, William (1999)
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    Constraints on New Physics from Long Baseline Neutrino Oscillation Experiments
    Honda, M.; Kao, Y.; Okamura, Naotoshi; Pronin, A.; Takeuchi, Tatsu (2007)
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    Constraints on R-parity violating couplings from CERN LEP and SLAG SLD hadronic observables
    Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2000-07-01)
    We analyze the one loop corrections to hadronic Z decays in an R-parity violating extension to the minimal supersymmetric standard model. Performing a global fit to all the hadronic observables at the Z peak, we obtain stringent constraints on the R-violating coupling constants lambda' and lambda". The presence of these couplings worsens the agreement with the data relative to the standard model. The strongest constraints come from the b asymmetry parameters A(b) and A(FB)(b) From a classical statistical analysis we find that the couplings lambda'(131), lambda'(132), and lambda"(321) are ruled out at the 1 sigma level, and that lambda'(133) and lambda"(33i) are ruled out at the 2 sigma level. A Bayesian statistical analysis weakens the bounds, but the corresponding chi(2)'s are uncomfortably large, rendering the relevance of the Bayesian bounds suspect.
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    Constraints on R-parity violating couplings from lepton universality
    Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2000-07-01)
    We analyze the one loop corrections to leptonic W and Z decays in an R-parity violating extension to the minimal supersymmetric standard model. We find that lepton universality violation in the Z line-shape variables alone would strengthen the bounds on the magnitudes of the lambda' couplings, but a global fit on all data leaves the bounds virtually unchanged at \lambda'(33k)\less than or equal to 0.42 and \lambda'(23k)\less than or equal to 0.50 at the 2 sigma level. Bounds from W decays are less stringent: \lambda'(33k)\less than or equal to 2.4 at 2 sigma, as a consequence of the weaker Fermilab experimental bounds on lepton universality violation in W decays. We also point out the potential of constraining R-parity violating couplings from the measurement of the Y invisible width.
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    Constraints on two-Higgs-doublet models at large tan beta from W and Z decays
    Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2000-09-01)
    We study constraints on type-II two-Higgs-doublet models at large tan beta from CERN LEP and SLD Z-pole data and from lepton universality violation in W decay. We perform a global fit and find that, in the context of Z decay, the LEP-SLD experimental values for lepton universality violation, R-b, and A(b) all somewhat disfavor the model. Contributions from the neutral-Higgs sector can be used to constrain the scalar-pseudoscalar Higgs mass splittings. Contributions from the charged-Higgs sector allow us to constrain the charged-Higgs boson mass. For tan beta=100 we obtain the 1 sigma classical (Bayesian) bounds of m(H+/-) greater than or equal to 670 GeV (370 GeV) and 1 greater than or equal to m(h)0/m(A)0/(alpha = beta) =m(H)0/m(A)0/(alpha=0) greater than or equal to 0.68 (0.64). The 2 sigma bounds are weak. Currently, the Fermilab Tevatron experimental limits on lepton universality violation in W decay provide no significant constraint on the Higgs sector.
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    The Contribution Of Galactic Free-Free Emission to Anisotropies in the Cosmic Microwave Background Found by the Saskatoon Experiment
    Simonetti, John H.; Dennison, B.; Topasna, G. A. (IOP PUBLISHING LTD, 1996-02)
    We made a sensitive, wide-field Ha image of the north celestial polar region. Using this image, we constrain the contribution of irregularities in interstellar free-free emission to the degree-scale anisotropies in the cosmic microwave background detected in recent observations at Saskatoon by the Princeton group. The analysis of the Her image mimics the Saskatoon data analysis: the resulting signal is the strength of irregularities sampled with the Saskatoon beam (i.e., degree-scale) along the 85 degrees declination circle. We found no such irregularities that could be attributed to Her emission. The implied upper bound on the rms variation in free-free brightness temperature is less than 4.6 mu K at 27.5 GHz. The observed cosmic microwave background anisotropies are much larger. Therefore, the contribution of irregularities in interstellar free-free emission to the observed anisotropies is negligible.
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    Detection in Hα of a Supershell Associated with W4
    Dennison, B.; Topasna, G. A.; Simonetti, John H. (IOP PUBLISHING LTD, 1997-01)
    From H I observations, Normandeau, Taylor, & Dewdney have identified a possible Galactic chimney emanating from W4. We observed a 10 degrees diameter field centered on this region in the Her line using a CCD camera sensitive to faint extended emission. Our image shows an apparent shell of H II, which we interpret as the ionized inner wall of a superbubble produced by stellar winds from the very young star cluster OCl 352. An analysis of the ionization balance indicates that much of the Lyman continuum radiation from the star cluster is absorbed and does not escape from the disk The shell appears to close 6 degrees (or about 230 pc) above the star cluster, and at a Galactic latitude of 7 degrees. The shell is quite elongated, with its major axis approximately perpendicular to the Galactic plane, as predicted for a superbubble formed in a stratified Galactic disk. The large size of the shell leads to an estimated age between 6.4 and 9.6 Myr, which exceeds that of OCl 352 (less than or similar to 2.5 Myr). The reason for this discrepancy is unclear, although it is possible that an earlier epoch of stellar outflow has contributed to the growth of the W4 superbubble.
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    The difficulties involved in calculating $δρ$
    Takeuchi, Tatsu; Grant, Aaron K.; Worah, Mihir P. (1995-04)
    We discuss the difficulties that arise when one tries to calculate $\delta\rho$ using dispersion relations.
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    Effect of the minimal length uncertainty relation on the density of states and the cosmological constant problem
    Chang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Takeuchi, Tatsu (American Physical Society, 2002-06-15)
    We investigate the effect of the minimal length uncertainty relation, motivated by perturbative string theory, on the density of states in momentum space. The relation is implemented through the modified commutation relation [(x) over cap (i),(p) over cap (j)]=i (h) over bar[(1+beta(p) over cap (2))delta(ij)+beta(')(p) over cap (i)(p) over cap (j)]. We point out that this relation, which is an example of a UV/IR relation, implies the finiteness of the cosmological constant. While our result does not solve the cosmological constant problem, it does shed new light on the relation between this outstanding problem and UV/IR correspondence. We also point out that the blackbody radiation spectrum will be modified at higher frequencies, but the effect is too small to be observed in the cosmic microwave background spectrum.
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    Exact solution of the harmonic oscillator in arbitrary dimensions with minimal length uncertainty relations
    Chang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Takeuchi, Tatsu (American Physical Society, 2002-06-15)
    We determine the energy eigenvalues and eigenfunctions of the harmonic oscillator where the coordinates and momenta are assumed to obey the modified commutation relations [(x) over cap (i),(p) over cap (j)]=i (h) over bar[(1+beta(p) over cap (2))delta(ij)+beta(')(p) over cap (i)(p) over cap (j)]. These commutation relations are motivated by the fact that they lead to the minimal length uncertainty relations which appear in perturbative string theory. Our solutions illustrate how certain features of string theory may manifest themselves in simple quantum mechanical systems through the modification of the canonical commutation relations. We discuss whether such effects are observable in precision measurements on electrons trapped in strong magnetic fields.
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    The Extreme Scattering Event toward PKS 1741-038: VLBI Images
    Lazio, T. J. W.; Fey, A. L.; Dennison, B.; Mantovani, F.; Simonetti, John H.; Alberdi, A.; Foley, A. R.; Fiedler, R.; Garrett, M. A.; Hirabayashi, H.; Jauncey, D. L.; Johnston, K. J.; Marcaide, J.; Migenes, V.; Nicolson, G. D.; Venturi, T. (IOP PUBLISHING LTD, 2000-05)
    We report multiepoch VLBI observations of the source PKS 1741-038 (OT 068) as it underwent an extreme scattering event (ESE). Observations at four epochs were obtained, and images were produced at three of these. One of these three epochs was when the source was near the minimum flux density of the ESE, the other two were as the flux density of the source was returning to its nominal value. The fourth epoch was at the maximum flux density during the egress from the ESE, but the VLBI observations had too few stations to produce an image. During the event the source consisted of a dominant, compact component, essentially identical to the structure seen outside the event. However, the source's diameter increased slightly at 13 cm, from near 0.6 mas outside the ESE to near 1 mas during the ESE. An increase in the source's diameter is inconsistent with a simple refractive model in which a smooth refractive lens drifted across the line of sight to PKS 1741-038. We also see no evidence for ESE-induced substructure within the source or the formation of multiple images, as would occur in a strongly refractive lens. However, a model in which the decrease in flux density during the ESE occurs solely because of stochastic broadening within the lens requires a larger broadening diameter during the event than is observed. Thus, the ESE toward PKS 1741-038 involved both stochastic broadening and refractive defocusing within the lens. If the structure responsible for the ESE has a size of order I AU, the level of scattering within an ESE lens may be a factor of 10(7) larger than that in the ambient medium. A filamentary structure could reduce the difference between the strength of scattering in the lens and ambient medium, but there is no evidence for a refractively induced elongation of the source. We conclude that, if ESEs arise from filamentary structures, they occur when the filamentary structures are seen lengthwise. We are able to predict the amount of pulse broadening that would result from a comparable lens passing in front of a pulsar. The pulse broadening would be no more than 1.1 mu s, consistent with the lack of pulse broadening detected during ESEs toward the pulsars PSR B1937+21 and PSR J1643-1224. The line of sight toward PKS 1741-038 is consistent with a turbulent origin for the structures responsible for ESEs. The source PKS 1741-038 lies near the radio Loop I and is seen through a local minimum in 100 mu m emission.
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    Galactic Foregrounds in Owens Valley Radio Observatory and UCSB South Pole 1994 Cosmic Microwave Background Anisotropy Data
    Mukherjee, P.; Dennison, B.; Ratra, B.; Simonetti, John H.; Ganga, K.; Hamilton, J. C. (IOP PUBLISHING LTD, 2002-11)
    We study Galactic emission foreground contamination of the Owens Valley Radio Observatory and UCSB South Pole 1994 cosmic microwave background anisotropy data by cross-correlating with templates of infrared dust emission and new high-resolution Virginia Tech Spectral Line Survey (VTSS) and Southern Halpha Sky Survey Atlas (SHASSA) Halpha data. Halpha data provide rough upper limits on the level of free-free emission in the data sets. The cross-correlation analysis does not contradict a two-component foreground emission hypothesis, with the two dust-correlated components being free-free emission and spinning-dust emission.
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    Glueball spectrum of pure Yang-Mills theory in 2+1 dimensions
    Leigh, R. G.; Minic, Djordje; Yelnikov, A. (American Physical Society, 2007-09)
    We present details of the analytic computation of the spectrum of lowest spin glueballs in pure Yang-Mills theory in 2+1 dimensions. The new ingredient is provided by the conjectured new nontrivial expression for the (quasi)Gaussian part of the ground state wave functional. We show that this wave functional can be derived by solving the Schrodinger equation under certain assumptions. The mass spectrum of the theory is determined by the zeros of Bessel functions, and the agreement with available lattice data is excellent.
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    Hydrogen-atom spectrum under a minimal-length hypothesis
    Benczik, S. Z.; Chang, Lay Nam; Minic, Djordje; Takeuchi, Tatsu (American Physical Society, 2005-07)
    The energy spectrum of the Coulomb potential with minimal length commutation relations [X-i, P-j] = ih{delta ij(1 + beta P-2) + beta PiPj} is determined both numerically and perturbatively for arbitrary values of beta'/beta and angular momenta l. The constraint on the minimal length scale from precision hydrogen spectroscopy data is of the order of a few GeV-1, weaker than previously claimed.
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    Hydrogen-atom spectrum under a minimal-length hypothesis
    Benczik, S. Z.; Chang, Lay Nam; Minic, Djordje; Takeuchi, Tatsu (American Physical Society, 2005-07-01)