40,888 research outputs found
Review of localization for 5d supersymmetric gauge theories
We give a pedagogical review of the localization of supersymmetric gauge
theory on 5d toric Sasaki-Einstein manifolds. We construct the cohomological
complex resulting from supersymmetry and consider its natural toric
deformations with all equivariant parameters turned on. We also give detailed
discussion on how the Sasaki-Einstein geometry permeates every aspect of the
calculation, from Killing spinor, vanishing theorems to the index theorems.Comment: This is a contribution to the review volume `Localization techniques
in quantum field theories' (eds. V. Pestun and M. Zabzine) which contains 17
Chapters. The complete volume is summarized in arXiv:1608.02952 and it can be
downloaded at https://arxiv.org/src/1608.02952/anc/LocQFT.pdf or
http://pestun.ihes.fr/pages/LocalizationReview/LocQFT.pd
The exclusive Drell-Yan process and deeply virtual pion production
In this talk it is reported on analyses of l p -> l pi+ n and pi- p -> l+ l-
n within the handbag approach. It is argued that recent measurements of hard
pion production performed by HERMES and CLAS clearly indicate the occurrence of
strong contributions from transversely polarized photons. The gamma*T -> pi
transitions are described by the transversity GPDs accompanied by twist-3 pion
wave functions. The experiments also require strong contributions from the pion
pole which can be modeled as a classical one-pion exchange. With these
extensions the handbag approach leads to results on cross sections and spin
asymmetries in fair agreement with experiment. This approach is also used for
an estimate of the partial cross sections for the exclusive Drell-Yan process.Comment: 8 pages, 6 figures, latex with style files jpsj-suppl.cls and
cite.sty invited talk presented at MENU2016, Kyoto (Japan), July 2016. arXiv
admin note: substantial text overlap with arXiv:1602.0380
Hard X-ray and UV Observations of the 2005 January 15 Two-ribbon Flare
In this paper, we present comprehensive analysis of a two-ribbon flare
observed in UV 1600{\AA} by Transition Region and Coronal Explorer and in HXRs
by Reuven Ramaty High Energy Solar Spectroscopic Imager. HXR (25-100 keV)
imaging observations show two kernels of size (FWHM) 15?? moving along the two
UV ribbons. We find the following results. (1) UV brightening is substantially
enhanced wherever and whenever the compact HXR kernel is passing, and during
the HXR transit across a certain region, the UV count light curve in that
region is temporally correlated with the HXR total flux light curve. After the
passage of the HXR kernel, the UV light curve exhibits smooth monotonical
decay. (2)We measure the apparent motion speed of the HXR sources and UV ribbon
fronts, and decompose the motion into parallel and perpendicular motions with
respect to the magnetic polarity inversion line (PIL). It is found that HXR
kernels and UV fronts exhibit similar apparent motion patterns and speeds. The
parallel motion dominates during the rise of the HXR emission, and the
perpendicular motion starts and dominates at the HXR peak, the apparent motion
speed being 10-40 km s-1. (3) We also find that UV emission is characterized by
a rapid rise correlated with HXRs, followed by a long decay on timescales of
15-30 minutes. The above analysis provides evidence that UV brightening is
primarily caused by beam heating, which also produces thick-target HXR
emission. The thermal origin of UV emission cannot be excluded, but would
produce weaker heating by one order of magnitude. The extended UV ribbons in
this event are most likely a result of sequential reconnection along the PIL,
which produces individual flux tubes (post-flare loops), subsequent non-thermal
energy release and heating in these flux tubes, and then the very long cooling
time of the transition region at the feet of these flux tubes.Comment: 8 figure
Single transverse-spin asymmetry in Drell-Yan lepton angular distribution
We calculate a single transverse-spin asymmetry for the Drell-Yan
lepton-pair's angular distribution in perturbative QCD. At leading order in the
strong coupling constant, the asymmetry is expressed in terms of a twist-3
quark-gluon correlation function T_F^{(V)}(x_1,x_2). In our calculation, the
same result was obtained in both light-cone and covariant gauge in QCD, while
keeping explicit electromagnetic current conservation for the virtual photon
that decays into the lepton pair. We also present a numerical estimate of the
asymmetry and compare the result to an existing other prediction.Comment: 15 pages, Revtex, 5 Postscript figures, uses aps.sty, epsfig.st
Solar flare hard X-ray spikes observed by RHESSI: a case study
In this paper, we analyze hard X-ray spikes observed by RHESSI to understand
their temporal, spectral, and spatial properties. A recently developed
demodulation code was applied to hard X-ray light curves in several energy
bands observed by RHESSI. Hard X-ray spikes were selected from the demodulated
flare light curves. We measured the spike duration, the energy-dependent time
delay, and count spectral index of these spikes. We also located the hard X-ray
source emitting these spikes from RHESSI mapping that was coordinated with
imaging observations in visible and UV wavelengths. We identify quickly varying
structures of <1 s during the rise of hard X-rays in five flares. These hard
X-ray spikes can be observed at photon energies over 100 keV. They exhibit
sharp rise and decay with a duration (FWHM) of less than 1 s. Energy-dependent
time lags are present in some spikes. It is seen that the spikes exhibit harder
spectra than underlying components, typically by 0.5 in the spectral index when
they are fitted to power-law distributions. RHESSI clean maps at 25-100 keV
with an integration of 2 s centered on the peak of the spikes suggest that hard
X-ray spikes are primarily emitted by double foot-point sources in magnetic
fields of opposite polarities. With the RHESSI mapping resolution of ~ 4 arsec,
the hard X-ray spike maps do not exhibit detectable difference in the spatial
structure from sources emitting underlying components. Coordinated
high-resolution imaging UV and infrared observations confirm that hard X-ray
spikes are produced in magnetic structures embedded in the same magnetic
environment of the underlying components. The coordinated high-cadence TRACE UV
observations of one event possibly reveal new structures on spatial scales <1-2
arsec at the time of the spike superposed on the underlying component. They are
probably sources of hard X-ray spikes.Comment: 20 pages, 11 figure
Solar flare hard X-ray spikes observed by RHESSI: a statistical study
Context. Hard X-ray (HXR) spikes refer to fine time structures on timescales
of seconds to milliseconds in high-energy HXR emission profiles during solar
flare eruptions. Aims. We present a preliminary statistical investigation of
temporal and spectral properties of HXR spikes. Methods. Using a three-sigma
spike selection rule, we detected 184 spikes in 94 out of 322 flares with
significant counts at given photon energies, which were detected from
demodulated HXR light curves obtained by the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI). About one fifth of these spikes are also
detected at photon energies higher than 100 keV. Results. The statistical
properties of the spikes are as follows. (1) HXR spikes are produced in both
impulsive flares and long-duration flares with nearly the same occurrence
rates. Ninety percent of the spikes occur during the rise phase of the flares,
and about 70% occur around the peak times of the flares. (2) The time durations
of the spikes vary from 0.2 to 2 s, with the mean being 1.0 s, which is not
dependent on photon energies. The spikes exhibit symmetric time profiles with
no significant difference between rise and decay times. (3) Among the most
energetic spikes, nearly all of them have harder count spectra than their
underlying slow-varying components. There is also a weak indication that spikes
exhibiting time lags in high-energy emissions tend to have harder spectra than
spikes with time lags in low-energy emissions.Comment: 16 pages, 13 figure
Prediction of destabilizing blade tip forces for shrouded and unshrouded turbines
The effect of a nonuniform flow field on the Alford force calculation is investigated. The ideas used here are based on those developed by Horlock and Greitzer. It is shown that the nonuniformity of the flow field does contribute to the Alford force calculation. An attempt is also made to include the effect of whirl speed. The values predicted by the model are compared with those obtained experimentally by Urlicks and Wohlrab. The possibility of using existing turbine tip loss correlations to predict beta is also exploited. The nonuniform flow field induced by the tip clearnance variation tends to increase the resultant destabilizing force over and above what would be predicted on the basis of the local variation of efficiency. On the one hand, the pressure force due to the nonuniform inlet and exit pressure also plays a part even for unshrouded blades, and this counteracts the flow field effects, so that the simple Alford prediction remains a reasonable approximation. Once the efficiency variation with clearance is known, the presented model gives a slightly overpredicted, but reasonably accurate destabilizing force. In the absence of efficiency vs. clearance data, an empirical tip loss coefficient can be used to give a reasonable prediction of destabilizing force. To a first approximation, the whirl does have a damping effect, but only of small magnitude, and thus it can be ignored for some purposes
Self-shadowing Effects of Slim Accretion Disks in Active Galactic Nuclei: Diverse Appearance of the Broad-line Region
Supermassive black holes in active galactic nuclei (AGNs) undergo a wide
range of accretion rates, which lead to diversity of appearance. We consider
the effects of anisotropic radiation from accretion disks on the broad-line
region (BLR), from the Shakura-Sunyaev regime to slim disks with
super-Eddington accretion rates. The geometrically thick funnel of the inner
region of slim disks produces strong self-shadowing effects that lead to very
strong anisotropy of the radiation field. We demonstrate that the degree of
anisotropy of the radiation fields grows with increasing accretion rate. As a
result of this anisotropy, BLR clouds receive different spectral energy
distributions depending on their location relative to the disk, resulting in
diverse observational appearance of the BLR. We show that the self-shadowing of
the inner parts of the disk naturally produces two dynamically distinct regions
of the BLR, depending on accretion rate. These two regions manifest themselves
as kinematically distinct components of the broad H line profile with
different line widths and fluxes, which jointly account for the Lorentzian
profile generally observed in narrow-line Seyfert 1 galaxies. In the time
domain, these two components are expected reverberate with different time lags
with respect to the varying ionizing continuum, depending on the accretion rate
and the viewing angle of the observer. The diverse appearance of the BLR due to
the anisotropic ionizing energy source can be tested by reverberation mapping
of H and other broad emission lines (e.g., \feii), providing a new tool
to diagnose the structure and dynamics of the BLR. Other observational
consequences of our model are also explored.Comment: emulatapj style, 15 pages, 6 figures, in pres
Chromospheric Evaporation in an X1.0 Flare on 2014 March 29 Observed with IRIS and EIS
Chromospheric evaporation refers to dynamic mass motions in flare loops as a
result of rapid energy deposition in the chromosphere. These have been observed
as blueshifts in X-ray and extreme-ultraviolet (EUV) spectral lines
corresponding to upward motions at a few tens to a few hundreds of km/s. Past
spectroscopic observations have also revealed a dominant stationary component,
in addition to the blueshifted component, in emission lines formed at high
temperatures (~10 MK). This is contradictory to evaporation models predicting
predominant blueshifts in hot lines. The recently launched Interface Region
Imaging Spectrograph (IRIS) provides high resolution imaging and spectroscopic
observations that focus on the chromosphere and transition region in the UV
passband. Using the new IRIS observations, combined with coordinated
observations from the EUV Imaging Spectrometer, we study the chromospheric
evaporation process from the upper chromosphere to corona during an X1.0 flare
on 2014 March 29. We find evident evaporation signatures, characterized by
Doppler shifts and line broadening, at two flare ribbons separating from each
other, suggesting that chromospheric evaporation takes place in successively
formed flaring loops throughout the flare. More importantly, we detect dominant
blueshifts in the high temperature Fe XXI line (~10 MK), in agreement with
theoretical predictions. We also find that, in this flare, gentle evaporation
occurs at some locations in the rise phase of the flare, while explosive
evaporation is detected at some other locations near the peak of the flare.
There is a conversion from gentle to explosive evaporation as the flare
evolves.Comment: ApJ in pres
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