118534156
Two-year monitoring of intra-day variability of quasar 1156+295 at 4.8 GHz
Aims. The quasar 1156+295 (4C +29.45) is one of the targets in the Urumqi monitoring program which aimed to search for evidence of annual modulation in the timescales of intra-day variable (IDV) sources.
7519824
Seven-frequency VLBI Observations of the GHz-Peaked-Spectrum Source OQ 208
We present quasi-simultaneous VLBI images of the GHz-Peaked-Spectrum radio source OQ 208 obtained with the Very Long Baseline Array at 1.4, 1.7, 2.3, 5.0, 8.4, 15.4 GHz and the European VLBI Network at 6.7 GHz. The low frequency (1.4, 1.7 and 2.3 GHz) observations reveal a weak and extended steep-spectrum component at about 30mas away at position angle -110 degrees, which may be a remnant emission. The radio structure of OQ 208 consists of two mini-lobes at 5.0, 6.7, 8.4 and 15.4 GHz. Our spectral analysis further confirms that the southwest lobe undergoes free-free absorption and finds that the free-free absorption is stronger in the inner region. By fitting the 8.4 GHz images from 1994 to 2005, we obtain a separation speed of 0.031+/-0.006 mas yr(-1) between the two mini-lobes. This indicates a jet proper motion of 0.105+/-0.020 c and a kinematic age of 219+/-42 yr for the radio source.
119119786
Radio observations of the first three-months of Fermi AGN at 4.8 GHz
Using the Urumqi 25 m radio telescope, sources from the first t hree months of the Fermi-large area telescope detected active galactic nuclei (AGN) catalog with a declination of > 0 ◦ were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the -ray intensity. Intra-day variability (IDV) observations were performed in March, April and May 2009 for 42 selected -ray bright blazars, and ∼60% of them showed evidence of flux variability at 4.8 GHz duri ng the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively "steeper" spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac objects: J0112+2244 and J0238+1636.
15928792
VLBI observations of nineteen GHz-peaked-spectrum radio sources at 1.6 GHz
$\mathsfsl{Aims~and~Methods}$. We present the results of VLBI observations of nineteen GHz-peaked-spectrum (GPS) radio sources at 1.6 GHz. Of them, 15 sources are selected from the Parkes half-jansky (PHJ) sample (Snellen et al. 2002, MNRAS, 337, 981), and 4 others are from our previous observation list. We aimed at imaging the structure of GPS sources, searching for compact symmetric objects (CSOs) and studying the absorption for the convex radio spectra of GPS sources. $\mathsfsl{Results}$. We obtained total-intensity 1.6 GHz VLBI images of 17 sources for the first time. Of them, 80% show a mini-double-lobe radio structure, indicating that they are CSOs or candidates, and their host AGNs could be edge-on to us. This result suggests that there is a high incidence of mini double-lobe sources (or CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232, J2058+0540, J2123-0112, and J2325-0344 are classified as CSOs with measured redshift, showing double-lobe structure with sizes of <1 kpc. Three sources J1057+0012, J1600-0037, and J1753+2750 are considered as core-jet sources according to their morphologies and flux variability.
118431275
IDV observations & study of the quasar 0917+624
We carried out intra-day variability (IDV) observations from August 2005 to January 2010 with the Urumqi 25 m radio telescope for a dozen IDV sources including the quasar 0917+624. This target exhibited pronounced centimeter-band, intra-day variability during the 1980s–1990s, but its strong IDV phase ceased in 2000. The source showed no IDV in the majority of the Urumqi observing sessions, although weak IDV activity was detected in some. Multifrequency UMRAO data for 0917+624 show that the spectral index is steeper during the weak and non-IDV phases than during the strong IDV phase, supporting the idea that the size of the scintillating component may be enlarged in the weak/non IDV phases.
118574295
Position Angle Changes of Inner-Jets in a Sample of Blazars
We have carried out the Gaussian model-fitting to 15 GHz VLBA cores for a sample of blazars from the MOJAVE database, analysed the correlations in the model-fitted parameters and studied the variability properties for different group of sources. We found that the Fermi LAT-detected blazars have on an average higher position angle changes of cores than the non-LAT detected blazars, and that the LAT-detected ones are associated with more variable cores in flux density.
18223996
Beauty is attractive: Moduli trapping at enhanced symmetry points
We study quantum effects on moduli dynamics arising from the production of particles which are light at points of enhanced symmetry in moduli space. The resulting forces trap the moduli at these points. Moduli trapping occurs in time-dependent quantum field theory, as well as in systems of moving D-branes, where it leads the branes to combine into stacks. Trapping also occurs in the presence of gravity, though the range over which the moduli can roll is limited by Hubble friction. We observe that a scalar field trapped on a steep potential can induce a stage of acceleration of the universe, which we call trapped inflation. Moduli trapping ameliorates the cosmological moduli problem and may affect vacuum selection. In particular, rolling moduli are most powerfully attracted to the points of greatest symmetry. Given suitable assumptions about the dynamics of the very early universe, this effect might help to explain why among the plethora of possible vacuum states of string theory, we appear to live in one with a large number of (spontaneously broken) symmetries.
118578199
$Z_b(10610)$ and $Z_b(10650)$ structures produced by the initial single pion emission in the $\Upsilon(5S)$ decays
We propose an unique mechanism called {\it Initial Single Pion Emission} existing in the $\Upsilon(5S)$ decays, and further study the line shapes of $d\Gamma(\Upsilon(5S\to \Upsilon(nS)\pi^+\pi^-))/dm_{\Upsilon(nS)\pi^+}$ ($n=1,2,3$) and $d\Gamma(\Upsilon(5S\to h_b(mP)\pi^+\pi^-))/dm_{h_b(mP)\pi^+}$ ($m=1,2$). We find sharp structures around 10610 MeV and 10650 MeV in the obtained theoretical line shapes of $d\Gamma(\Upsilon(5S\to \Upsilon(nS)\pi^+\pi^-))/dm_{\Upsilon(nS)\pi^+}$ and $d\Gamma(\Upsilon(5S\to h_b(mP)\pi^+\pi^-))/dm_{h_b(mP)\pi^+}$ distributions, which could naturally correspond to the $Z_b(10610)$ and $Z_b(10650)$ structures newly observed by Belle.
13990506
Dynamics study of Z+(4430) and X(3872) in molecular picture
In this talk, we review our recent work about the dynamical studies of Z+(4430) and X(3872). Z+(4430) can not be explained as a D1′D* or D1D* molecular state only considering one pion exchange potential without the cutoff, which needs to be confirmed by introducing sigma exchange potential and adding the cutoff in the effective potential. One also excludes the possibility of X(3872) as a DD* molecular state by one pion and one sigma exchanges with the cutoff. Fortunately there exists an S‐wave BB* bound state with JPC = 1++. we suggest future experiment to search this state.
28437592
A possible global group structure for exotic states
Based on the fact that the long expected pentaquark which possesses the exotic quantum numbers of $$B=1$$B=1 and $$S=1$$S=1 was not experimentally found, although exotic states of $$XYZ$$XYZ have been observed recently, we conjecture that the heavy flavors may play an important role in stabilizing the hadronic structures beyond the traditional $$q\bar{q}$$qq¯ and $$qqq$$qqq composites.
17413397
Understanding the newly observed Y(4008) by Belle
Very recently a new enhancement around 4.05 GeV was observed by the Belle experiment. We discuss some possible assignments for this enhancement, i.e. the ψ(3S) and D*D̄* molecular states. In these two assignments, Y(4008) can decay into J/ψπ0π0 with a branching ratio comparable with that of Y(4008)→J/ψπ+π-. Thus, one suggests high energy experimentalists to look for Y(4008) in J/ψπ0π0 channel. Furthermore one proposes further experiments to search for the missing channels DD̄, DD̄*+h.c. and especially χcJπ+π-π0 and ηcπ+π-π0, which will be helpful to distinguish the ψ(3S) and D*D̄* molecular state assignments for this new enhancement.