809 research outputs found
The Higgs Boson: Shall We See It Soon Or Is It Still Far Away?
The status of the Higgs boson mass in the Standard Model and its
supersymmetric extensions is reviewed and the perspectives of Higgs searches
are discussed. The parameter space of the Minimal Supersymmetric Standard Model
(MSSM) is analysed with the emphasis on the lightest Higgs mass. The infrared
behaviour of renormalization group equations for the parameters of MSSM is
examined and infrared quasi-fixed points are used for the Higgs mass
predictions. They strongly suggest the Higgs mass to be lighter than 100 or 130
GeV for low and high scenarios, respectively. Extended models,
however, allow one to increase these limits for low up to 50%.Comment: 13 pages, LaTex, 4 ps figures, Submitted to special issue of
Phys.Reports dedicated to 70th birthday of L.B.Oku
Direct Spectroscopic Identification of the Origin of 'Green Fuzzy' Emission in Star Forming Regions
"Green fuzzies" or "extended green objects" were discovered in the recent
Spitzer GLIMPSE survey data. These extended sources have enhanced emission in
the 4.5um IRAC channel images (which are generally assigned to be green when
making 3-color RGB images from Spitzer data). Green fuzzies are frequently
found in the vicinities of massive young stellar objects, and it has been
established that they are in some cases associated with outflows. Nevertheless,
the spectral carrier(s) of this enhanced emission is still uncertain. Although
it has been suggested that Br Alpha, H2, [Fe II], and/or broad CO emission may
be contributing to and enhancing the 4.5um flux from these objects, to date
there have been no direct observations of the 4-5um spectra of these objects.
We report here on the first direct spectroscopic identification of the origin
of the green fuzzy emission. We obtained spatially resolved L and M band
spectra for two green fuzzy sources using NIRI on the Gemini North telescope.
In the case of one source, G19.88-0.53, we detect three individual knots of
green fuzzy emission around the source. The knots exhibit a pure molecular
hydrogen line emission spectrum, with the 4.695um v=0-0 S(9) line dominating
the emission in the 4-5um wavelength range, and no detected continuum
component. Our data for G19.88-0.53 prove that green fuzzy emission can be due
primarily to emission lines of molecular hydrogen within the bandpass of the
IRAC 4.5um channel. However, the other target observed, G49.27-0.34, does not
exhibit any line emission and appears to be an embedded massive young stellar
object with a cometary UC HII region. We suggest that the effects of extinction
in the 3-8um wavelength range and an exaggeration in the color stretch of the
4.5um filter in IRAC RGB images could lead to embedded sources such as this one
falsely appearing "green".Comment: 10 pages, 5 figures; Accepted for publication by A
Universality and the approach to the continuum limit in lattice gauge theory
The universality of the continuum limit and the applicability of renormalized
perturbation theory are tested in the SU(2) lattice gauge theory by computing
two different non-perturbatively defined running couplings over a large range
of energies. The lattice data (which were generated on the powerful APE
computers at Rome II and DESY) are extrapolated to the continuum limit by
simulating sequences of lattices with decreasing spacings. Our results confirm
the expected universality at all energies to a precision of a few percent. We
find, however, that perturbation theory must be used with care when matching
different renormalized couplings at high energies.Comment: 33 pages, 172 kB uu-tar-compressed ps-fil
Non-perturbative O(a) improvement of lattice QCD
The coefficients multiplying the counterterms required for O() improvement
of the action and the isovector axial current in lattice QCD are computed
non-perturbatively, in the quenched approximation and for bare gauge couplings
in the range . A finite-size method based on the
Schr\"odinger functional is employed, which enables us to perform all
calculations at zero or nearly zero quark mass. As a by-product the critical
hopping parameter is obtained at all couplings considered.Comment: typo in eq. (7.3) corrected; 26 pages, postscript fil
Radiative Electroweak Symmetry Breaking and the Infrared Fixed Point of the Top Quark Mass
The infrared quasi fixed point solution for the top quark mass in the Minimal
Supersymmetric Standard Model explains in a natural way large values of the top
quark mass and appears as a prediction in many interesting theoretical schemes.
Moreover, as has been recently pointed out, for moderate values of ,
in order to achieve gauge and bottom-tau Yukawa coupling unification, the top
quark mass must be within of its fixed point value. In this work we
show that the convergence of the top quark mass to its fixed point value has
relevant consequences for the (assumed) universal soft supersymmetry breaking
parameters at the grand unification scale. In particular, we show that the low
energy parameters do not depend on and but on the combination
. Hence, there is a reduction in the number of
independent parameters. Most interesting, the radiative
breaking condition implies strong correlations between the supersymmetric mass
parameter and the supersymmetry breaking parameters and
or . These correlations, which become stronger for , may have some fundamental origin, which would imply the need of a
reformulation of the naive fine tuning criteria.Comment: 17 pages, 5 figures, CERN-TH.7060/9
Theory of Gamma-Ray Burst Emission in Light of BSAX Results
We briefly discuss the theoretical implications of recent detections of
gamma-ray bursts (GRBs) by BSAX. Relativistic shock wave theories of fireball
expansion are challenged by the wealth of X-ray, optical and radio data
obtained after the discovery of the first X-ray GRB afterglow. BSAX data
contribute to address several issues concerning the initial and afterglow GRB
emission. The observations also raise many questions that are still unsolved.
The synchrotron shock model is in very good agreement with time-resolved
broad-band spectra (2-500 keV) for the majority of GRBs detected by BSAX.Comment: 8 pages, LATEX text plus two postscript figures included. To appear
in the Proceedings of the Accademia dei Lincei Symposium: "The Active X-ray
Sky: Results from Beppo-SAX and Rossi-XTE", Nuclear Physics B Proceedings
Supplement, eds. L. Scarsi et a
SUMOylation of nuclear actin
Actin, a major component of the cytoplasm, is also abundant in the nucleus. Nuclear actin is involved in a variety of nuclear processes including transcription, chromatin remodeling, and intranuclear transport. Nevertheless, the regulation of nuclear actin by posttranslational modifications has not been investigated. We now show that nuclear actin is modified by SUMO2 and SUMO3 and that computational modeling and site-directed mutagenesis identified K68 and K284 as critical sites for SUMOylating actin. We also present a model for the actin–SUMO complex and show that SUMOylation is required for the nuclear localization of actin
The top-quark mass in SU(5)xU(1) supergravity
We show that the currently experimentally preferred values of the top-quark
mass (\ie, 130\lsim m_t\lsim180\GeV) are naturally understood in the context
of string models, where the top-quark Yukawa coupling at the string scale is
generically given by , with the unified gauge
coupling. A detailed study of the Yukawa sector of
supergravity shows that the ratio of the bottom-quark to tau-lepton Yukawa
couplings at the string scale is required to be in the range
0.7\lsim\lambda_b/\lambda_\tau\lsim1, depending on the values of and
. This result is consistent with symmetry, which does
{\em not} require the equality of these Yukawa couplings in the unbroken
symmetry phase of the theory. As a means of possibly predicting the value of
, we propose a procedure whereby the size of the allowed parameter space
is determined as a function of , since all sparticle and Higgs-boson
masses and couplings depend non-trivially on . At present, no significant
preference for particular values of in supergravity is
observed, except that high-precision LEP data requires m_t\lsim180\GeV.Comment: latex, 10 pages, 4 figures (included), CERN-TH.7138/94,
CTP-TAMU-05/9
Aromatic Hydrocarbons, Diamonds, and Fullerenes in Interstellar Space: Puzzles to be Solved by Laboratory and Theoretical Astrochemistry
New research is presented, and previous research is reviewed, on the emission
and absorption of interstellar aromatic hydrocarbons. Emission from aromatic
hydrocarbons dominate the mid-infrared emission of many galaxies, including our
own Milky Way galaxy. Only recently have aromatic hydrocarbons been observed in
absorption in the interstellar medium, along lines of sight with high column
densities of interstellar gas and dust. Much work on interstellar aromatics has
been done, with astronomical observations and laboratory and theoretical
astrochemistry. In many cases the predictions of laboratory and theoretical
work are confirmed by astronomical observations, but in other cases clear
discrepancies exist which provide problems to be solved by a combination of
astronomical observations, laboratory studies, and theoretical studies. The
emphasis of this paper will be on current outstanding puzzles concerning
aromatic hydrocarbons which require further laboratory and theoretical
astrochemistry to resolve. This paper will also touch on related topics where
laboratory and theoretical astrochemistry studies are needed to explain
astrophysical observations, such as a possible absorption feature due to
interstellar "diamonds" and the search for fullerenes in space.Comment: Spectrochimica Acta A, Feb. 2001, in press. 33 pages including 11
postscript figures, AASTeX format. Full postscript paper also available at
http://www.astronomy.ohio-state.edu/~sellgren/saa.htm
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