5,356 research outputs found
Inflationary NonGaussianity from Thermal Fluctuations
We calculate the contribution of the fluctuations with the thermal origin to
the inflationary nonGaussianity. We find that even a small component of
radiation can lead to a large nonGaussianity. We show that this thermal
nonGaussianity always has positive . We illustrate our result in
the chain inflation model and the very weakly dissipative warm inflation model.
We show that is general in such models. If we allow
modified equation of state, or some decoupling effects, the large thermal
nonGaussianity of order or even can be
produced. We also show that the power spectrum of chain inflation should have a
thermal origin. In the Appendix A, we made a clarification on the different
conventions used in the literature related to the calculation of .Comment: 20 pages, 1 figure. v2, v3: references and acknowledgments update
Generalized Space-time Noncommutative Inflation
We study the noncommutative inflation with a time-dependent noncommutativity
between space and time. From the numerical analysis of power law inflation,
there are clues that the CMB spectrum indicates a nonconstant noncommutative
inflation. Then we extend our treatment to the inflation models with more
general noncommutativity and find that the scalar perturbation power spectrum
depends sensitively on the time varying of the spacetime noncommutativity. This
stringy effect may be probed in the future cosmological observations.Comment: 15 pages, 2 figure
RIS-Assisted Self-Interference Mitigation for In-Band Full-Duplex Transceivers
The wireless in-band full-duplex (IBFD) technology can in theory double the
system capacity over the conventional frequency division duplex (FDD) or
time-division duplex (TDD) alternatives. But the strong self-interference of
the IBFD can cause excessive quantization noise in the analog-to-digital
converters (ADC), which represents the hurdle for its real implementation. In
this paper, we consider employing a reconfigurable intelligent surface (RIS)
for IBFD communications. While the BS transmits and receives the signals to and
from the users simultaneously on the same frequency band, it can adjust the
reflection coefficients of the RIS to configure the wireless channel so that
the self-interference of the BS is sufficiently mitigated in the propagation
domain. Taking the impact of the quantization noise into account, we propose to
jointly design the downlink (DL) precoding matrix and the RIS coefficients to
maximize the sum of uplink (UL) and DL rates. The effectiveness of the proposed
RIS-assisted in-band full-duplex (RAIBFD) system is verified by simulation
studies, even taking into considerations that the phases of the RIS have only
finite resolution.Comment: 11 page
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