arXiv subjects

G. Park

Publications and source records attributed to G. Park.

6 recordsLinked to original sources

arXiv2019

CHIMPS: Physical properties of molecular clumps across the inner Galaxy

The latest generation of high-angular-resolution unbiased Galactic plane surveys in molecular-gas tracers are enabling the interiors of molecular clouds to be studied across a range of environments. The CHIMPS survey simultaneously mapped a sector of the inner Galactic plane, within 27.8 < l < 46.2 deg and |b| < 0.5 deg, in 13CO and C18O (3-2) at 15 arcsec resolution. The combination of CHIMPS data with 12CO (3-2) data from the COHRS survey has enabled us to perform a voxel-by-voxel local-thermodynamic-equilibrium analysis, determining the excitation temperature, optical depth, and column density of 13CO at each l,b,v position. Distances to discrete sources identified by FellWalker in the 13CO (3-2) emission maps were determined, allowing the calculation of numerous physical properties of the sources, and we present the first source catalogues in this paper. We find that, in terms of size and density, the CHIMPS sources represent an intermediate population between large-scale molecular clouds identified by CO and dense clumps seen in dust emission, and therefore represent the bulk transition from the diffuse to the dense phase of molecular gas. We do not find any significant systematic variations in the masses, column densities, virial parameters, excitation temperature, or the turbulent pressure over the range of Galactocentric distance probed, but we do find a shallow increase in the mean volume density with increasing Galactocentric distance. We find that inter-arm clumps have significantly narrower linewidths, and lower virial parameters and excitation temperatures than clumps located in spiral arms. When considering the most reliable distance-limited subsamples, the largest variations occur on the clump-to-clump scale, echoing similar recent studies that suggest that the star-forming process is largely insensitive to the Galactic-scale environment, at least within the inner disc.

astro-ph.GA↗

arXiv1994

Experimental aspects of SU(5)xU(1) supergravity

We study various aspects of $SU(5)\times U(1)$ supergravity as they relate to the experimental verification or falsification of this model. We consider two string-inspired, universal, one-parameter, no-scale soft-supersymmetry-breaking scenarios, driven by the $F$-terms of the moduli and dilaton fields. The model is described in terms of the supersymmetry mass scale (\ie, the chargino mass $m_{χ^\pm_1}$), $\tanβ$, and the top-quark mass. We first determine the combined effect on the parameter space of all presently available direct and indirect experimental constraints, including the LEP lower bounds on sparticle and Higgs-boson masses, the $b\to sγ$ rate, the anomalous magnetic moment of the muon, the high-precision electroweak parameters $ε_1,ε_b$ (which imply $m_t\lsim180\GeV$), and the muon fluxes in underground detectors (neutrino telescopes). For the still-allowed points in $(m_{χ^\pm_1},\tanβ)$ parameter space, we re-evaluate the experimental situation at the Tevatron, LEPII, and HERA. In the 1994 run, the Tevatron could probe chargino masses as high as 100 GeV. At LEPII the parameter space could be explored with probes of different resolutions: Higgs boson searches, selectron searches, and chargino searches. Moreover, for $m_t\lsim150\GeV$, these Higgs-boson searches could explore all of the allowed parameter space with $\sqrt{s}\lsim210\GeV$.

hep-ph↗

arXiv1993

First Constraints on SU(5)xU(1) Supergravity from Trilepton Searches at the Tevatron

We present the first constraints on the parameter space of $SU(5)\times U(1)$ supergravity (in both no-scale and dilaton scenarios) which arise from the recently announced limits on trilepton searches at the Tevatron. The trilepton rate has been calculated for those points in parameter space which satisfy not only the minimal theoretical and experimental LEP constraints, but also the {\em combined} effect of the following indirect experimental constraints: (i) the CLEO limits on the $b\to sγ$ rate, (ii) the long-standing limit on the anomalous magnetic moment of the muon, (iii) the non-observation of anomalous muon fluxes in underground detectors (``neutrino telescopes"), and (iv) the electroweak LEP high-precision measurements in the form of the $ε_{1},ε_b$ parameters. For $m_t=150\GeV$, the trilepton constraint rules out some regions of parameter space with chargino masses as high as $m_{χ^\pm_1}\approx105\GeV$, although it is not possible to establish a new absolute lower bound on the chargino mass. For $m_t=170\GeV$, the simultaneous imposition of {\em all} of the above constraints excludes the dilaton scenario completely, and leaves only a few allowed points in parameter space in the no-scale scenario (with $m_{\tilde q}\approx m_{\tilde g}\lsim285\GeV$). The five-fold increase in integrated luminosity expected in the upcoming Tevatron run should probe some regions of parameter space with chargino masses much beyond the reach of LEPII.

hep-ph↗

arXiv1993

The strongest experimental constraints on SU(5)xU(1) supergravity models

We consider a class of well motivated string-inspired flipped $SU(5)$ supergravity models which include four supersymmetry breaking scenarios: no-scale, strict no-scale, dilaton, and special dilaton, such that only three parameters are needed to describe all new phenomena $(m_t,\tanβ,m_{\tilde g})$. We show that the LEP precise measurements of the electroweak parameters in the form of the $ε_1$ variable, and the CLEOII allowed range for $\bsg$ are at present the most important experimental constraints on this class of models. For $m_t\gsim155\,(165)\GeV$, the $ε_1$ constraint (at 90(95)\%CL) requires the presence of light charginos ($m_{χ^\pm_1}\lsim50-100\GeV$ depending on $m_t$). Since all sparticle masses are proportional to $m_{\tilde g}$, $m_{χ^\pm_1}\lsim100\GeV$ implies: $m_{χ^0_1}\lsim55\GeV$, $m_{χ^0_2}\lsim100\GeV$, $m_{\tilde g}\lsim360\GeV$, $m_{\tilde q}\lsim350\,(365)\GeV$, $m_{\tilde e_R}\lsim80\,(125)\GeV$, $m_{\tilde e_L}\lsim120\,(155)\GeV$, and $m_{\tildeν}\lsim100\,(140)\GeV$ in the no-scale (dilaton) flipped $SU(5)$ supergravity model. The $\bsg$ constraint excludes a significant fraction of the otherwise allowed region in the $(m_{χ^\pm_1},\tanβ)$ plane (irrespective of the magnitude of the chargino mass), while future experimental improvements will result in decisive tests of these models. In light of the $ε_1$ constraint, we conclude that the outlook for chargino and selectron detection at LEPII and at HERA is quite favorable in this class of models.

hep-ph↗

arXiv1993

Precision Electroweak Tests of the Minimal and Flipped SU(5) Supergravity Models

We explore the one-loop electroweak radiative corrections in the minimal $SU(5)$ and the no-scale flipped $SU(5)$ supergravity models via explicit calculation of vacuum polarization contributions to the $ε_{1,2,3}$ parameters. Experimentally, $ε_{1,2,3}$ are obtained from a global fit to the LEP observables, and $M_W/M_Z$ measurements. We include $q^2$-dependent effects which have been neglected in most previous ``model-independent" analyses of this type. These effects induce a large systematic negative shift on $ε_{1,2,3}$ for light chargino masses ($m_{χ^\pm_1}\lsim70\GeV$). In agreement with previous general arguments, we find that for increasingly large sparticle masses, the heavy sector of both models rapidly decouples, \ie, the values for $ε_{1,2,3}$ quickly asymptote to the Standard Model values with a {\it light} Higgs ($m_{H_{SM}}\sim100\GeV$). Specifically, at present the $90\%$ CL upper limit on the top-quark mass is $m_t\lsim175\GeV$ in the no-scale flipped $SU(5)$ supergravity model. These bounds can be strengthened for increasing chargino masses in the $50-100\GeV$ interval. In particular, for $m_t\gsim160\GeV$, the Tevatron may be able to probe through gluino($\tilde g$) and squark($\tilde q$) production up to $m_{\tilde g}\approx m_{\tilde q}\approx250\GeV$, exploring at least half of the parameter space in this model.

hep-ph↗

arXiv1993

Probing supergravity models with the $b\to sγ$ microscope

We present a calculation of the branching ratio $\brbsg$ in two well motivated supersymmetric models: the minimal $SU(5)$ and the no-scale flipped $SU(5)$ supergravity models. We find that the improved CLEO upper bound ($\brbsg<5.4\times10^{-4}$ at 95\% CL) does not yet constrain the minimal $SU(5)$ supergravity model, where $\brbsg_{minimal}=(2.3-3.6)\times10^{-4}$. In the flipped $SU(5)$ model the CLEO bound is constraining, although still not very significantly, even for light charged Higgs masses. An improvement in sensitivity by a factor of two will probe all (more than half) of the parameter space of the minimal (flipped) $SU(5)$ supergravity model. This ``resolution" of the $\bsg$ microscope far surpasses that of present collider experiments. In the flipped model there exists a significant region of parameter space where $\brbsg$ is highly suppressed due to a new phenomenon involving a complicated cancellation against the QCD correction parameter.

hep-ph↗