767 research outputs found
Towards the physical vacuum of cosmic inflation
There have been long debates about the initial condition of inflationary
perturbations. In this work we explicitly show the decay of excited states
during inflation via interactions. For this purpose, we note that the folded
shape non-Gaussianity can be interpreted as the decay of the non-Bunch-Davies
initial condition. The one loop diagrams with non-Bunch-Davies propagators are
calculated to uncover the decay of such excited states. The observed smallness
of non-Gaussianity keeps the window open for probing inflationary initial
conditions and trans-Planckian physics
Supersymmetry Deformations, Electromagnetic Duality and Dirac-Born-Infeld Actions
We study the general deformation of supersymmetry
transformations of a vector multiplet that forms a (constant) triplet under the
R-symmetry corresponding to the magnetic dual of the triplet of the
Fayet-Iliopoulos (FI) parameters. We show that in the presence of both
triplets, the induced scalar potential of a vector multiplet with generic
prepotential has always a minimum that realises partial breaking of supersymmetry. We then consider the impact of the
deformation in the Dirac-Born-Infeld (DBI) action where one supersymmetry is
non-linearly realised, described by a nilpotent constraint on the deformed
chiral-chiral superfield. We show that the generic magnetic
deformation induces an ordinary FI D-term along the linear supersymmetry via
the theta-angle. Moreover, we argue that the resulting action differs on-shell
from the standard one (DBI+FI) by fermionic contributions.Comment: 28 page
Celestial Mellin Amplitude
Celestial holography provides a promising avenue to studying bulk scattering
in flat spacetime from the perspective of boundary celestial conformal field
theory (CCFT). A key ingredient in connecting the two sides is the celestial
amplitude, which is given by the Mellin transform of momentum space scattering
amplitude in energy. As such, celestial amplitudes can be identified with the
correlation functions in celestial conformal field theory. In this paper, we
introduce the further notion of celestial Mellin amplitude, which is given by
the Mellin transform of celestial amplitude in coordinate. For technical
reasons, we focus on the celestial Mellin amplitudes for scalar fields in three
dimensional flat spacetime dual to 1D CCFT, and discuss the celestial Mellin
block expansion. In particular, the poles of the celestial Mellin amplitude
encode the scaling dimensions of the possible exchanged operators, while the
residues there are related to the OPE coefficient squares in a linear and
explicit way. We also compare the celestial Mellin amplitudes with the
coefficient functions which can be obtained using inversion formulae. Finally,
we make some comments about the possible generalizations of celestial Mellin
amplitudes to higher dimensions
deformations with supersymmetry
We investigate the behaviour of two-dimensional quantum field theories with
supersymmetry under a deformation induced by the
`' composite operator. We show that the deforming operator can be
defined by a point-splitting regularisation in such a way as to preserve
supersymmetry. As an example of this construction, we work
out the deformation of a free theory and compare to that
induced by the Noether stress-energy tensor. Finally, we show that the
supersymmetric deformed action actually possesses
symmetry, half of which is non-linearly realised
Echoes of Inflationary First-Order Phase Transitions in the CMB
Cosmological phase transitions (CPTs), such as the Grand Unified Theory (GUT)
and the electroweak (EW) ones, play a significant role in both particle physics
and cosmology. In this letter, we propose to probe the first-order CPTs, by
detecting gravitational waves (GWs) which are generated during the phase
transitions through the cosmic microwave background (CMB). If happened around
the inflation era, the first-order CPTs may yield low-frequency GWs due to
bubble dynamics, leaving imprints on the CMB. In contrast to the nearly
scale-invariant primordial GWs caused by vacuum fluctuation, these
bubble-generated GWs are scale dependent and have non-trivial B-mode spectra.
If decoupled from inflaton, the EWPT during inflation may serve as a probe for
the one after reheating where the baryon asymmetry could be generated via EW
baryogenesis (EWBG). The CMB thus provides a potential way to test the
feasibility of the EWBG, complementary to the collider measurements of Higgs
potential and the direct detection of GWs generated during EWPT.Comment: 5+6 pages, 4 figures. V2 changed title, added one figure about
constraints of Planck2015+BICEP2/Keck data, added references and removed
appendix. Accepted by PL
Inconsistencies of interannual variability and trends in long-term satellite leaf area index products
Understanding the long-term performance of global satellite leaf area index (LAI) products is important for global change research. However, few effort has been devoted to evaluating the long-term time-series consistencies of LAI products. This study compared four long-term LAI products (GLASS, GLOBMAP, LAI3g, and TCDR) in terms of trends, interannual variabilities, and uncertainty variations from 1982 through 2011. This study also used four ancillary LAI products (GEOV1, MERIS, MODIS C5, and MODIS C6) from 2003 through 2011 to help clarify the performances of the four long-term LAI products. In general, there were marked discrepancies between the four long-term LAI products. During the pre-MODIS period (1982-1999), both linear trends and interannual variabilities of global mean LAI followed the order GLASS>LAI3g>TCDR>GLOBMAP. The GLASS linear trend and interannual variability were almost 4.5 times those of GLOBMAP. During the overlap period (2003-2011), GLASS and GLOBMAP exhibited a decreasing trend, TCDR no trend, and LAI3g an increasing trend. GEOV1, MERIS, and MODIS C6 also exhibited an increasing trend, but to a much smaller extent than that from LAI3g. During both periods, the R2 of detrended anomalies between the four long-term LAI products was smaller than 0.4 for most regions. Interannual variabilities of the four long-term LAI products were considerably different over the two periods, and the differences followed the order GLASS>LAI3g>TCDR>GLOBMAP. Uncertainty variations quantified by a collocation error model followed the same order. Our results indicate that the four long-term LAI products were neither intraconsistent over time nor interconsistent with each other. These inconsistencies may be due to NOAA satellite orbit changes and MODIS sensor degradation. Caution should be used in the interpretation of global changes derived from the four long-term LAI products
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