3,771 research outputs found
High brightness fully coherent X-ray amplifier seeded by a free-electron laser oscillator
X-ray free-electron laser oscillator (XFELO) is expected to be a cutting edge
tool for fully coherent X-ray laser generation, and undulator taper technique
is well-known for considerably increasing the efficiency of free-electron
lasers (FELs). In order to combine the advantages of these two schemes, FEL
amplifier seeded by XFELO is proposed by simply using a chirped electron beam.
With the right choice of the beam parameters, the bunch tail is within the gain
bandwidth of XFELO, and lase to saturation, which will be served as a seeding
for further amplification. Meanwhile, the bunch head which is outside the gain
bandwidth of XFELO, is preserved and used in the following FEL amplifier. It is
found that the natural "double-horn" beam current as well as residual energy
chirp from chicane compressor are quite suitable for the new scheme. Inheriting
the advantages from XFELO seeding and undulator tapering, it is feasible to
generate nearly terawatt level, fully coherent X-ray pulses with unprecedented
shot-to-shot stability, which might open up new scientific opportunities in
various research fields.Comment: 8 pages, 8 figure
Model-Independent Constraints on Lorentz Invariance Violation via the Cosmographic Approach
Since Lorentz invariance plays an important role in modern physics, it is of
interest to test the possible Lorentz invariance violation (LIV). The time-lag
(the arrival time delay between light curves in different energy bands) of
Gamma-ray bursts (GRBs) has been extensively used to this end. However, to our
best knowledge, one or more particular cosmological models were assumed {\it a
priori} in (almost) all of the relevant works in the literature. So, this makes
the results on LIV in those works model-dependent and hence not so robust in
fact. In the present work, we try to avoid this problem by using a
model-independent approach. We calculate the time delay induced by LIV with the
cosmic expansion history given in terms of cosmography, without assuming any
particular cosmological model. Then, we constrain the possible LIV with the
observational data, and find weak hints for LIV.Comment: 15 pages, 4 figures, 3 tables, revtex4; v2: discussions added, Phys.
Lett. B in pres
Criticality in Gauged Supergravities
AdS black holes show richer transition behaviors in extended phase space by
assuming the cosmological constant and its conjugate quantity to behave like
thermodynamic pressure and thermodynamic volume. We study the extended
thermodynamics of charged dilatonic AdS black holes in a class of
Einstein-Maxwell-dilaton theories that can be embedded in gauged supergravities
in various dimensions. We find that the transition behaviors of higher
dimensional dilatonic AdS black holes are different from the four dimensional
counterparts, and new transition behaviors emerges in higher dimensions. First,
there exists standard Van der Waals transition only in a five dimensional
dilatonic AdS black hole with two equal charges. Second, there emerge a new
phase transition branch in negative pressure region in six and seven
dimensional dilatonic black holes with two equal charges. Third, there emerge
transition behaviors in higher dimensional black hole with single charge cases,
which are absent in four dimensions.Comment: Latex, 18 pages, 8 figures; published versio
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