14,611 research outputs found
The Strong Multifield Slowroll Condition and Spiral Inflation
We point out the existing confusions about the slowroll parameters and
conditions for multifield inflation. If one requires the fields to roll down
the gradient flow, we find that only articles adopting the Hubble slowroll
expansion are on the right track, and a correct condition can be found in a
recent book by Liddle and Lyth. We further analyze this condition and show that
the gradient flow requirement is stronger than just asking for a slowly
changing, quasi-de Sitter solution. Therefore it is possible to have a
multifield slowroll model that does not follow the gradient flow. Consequently,
it no longer requires the gradient to be small. It even bypasses the first
slowroll condition and some related no-go theorems from string theory. We
provide the "spiral inflation" as a generic blueprint of such inflation model
and show that it relies on a monodromy locus---a common structure in string
theory effective potentials.Comment: 12 pages, version 4, cosmetic changes recommended by referee,
resubmitting to PR
Probability of Slowroll Inflation in the Multiverse
Slowroll after tunneling is a crucial step in one popular framework of the
multiverse---false vacuum eternal inflation (FVEI). In a landscape with a large
number of fields, we provide a heuristic estimation for its probability. We
find that the chance to slowroll is exponentially suppressed, where the
exponent comes from the number of fields. However, the relative probability to
have more e-foldings is only mildly suppressed as with
. Base on these two properties, we show that the FVEI picture is
still self-consistent and may have a strong preference between different
slowroll models.Comment: version 3, 21 pages, resubmit to PRD recommanded by refere
Coupled rotor-body vibrations with inplane degrees of freedom
In an effort to understand the vibration mechanisms of helicopters, the following basic studies are considered. A coupled rotor-fuselage vibration analysis including inplane degrees of freedom of both rotor and airframe is performed by matching of rotor and fuselage impedances at the hub. A rigid blade model including hub motion is used to set up the rotor flaplag equations. For the airframe, 9 degrees of freedom and hub offsets are used. The equations are solved by harmonic balance. For a 4-bladed rotor, the coupled responses and hub loads are calculated for various parameters in forward flight. The results show that the addition of inplane degrees of freedom does not significantly affect the vertical vibrations for the cases considered, and that inplane vibrations have similar resonance trends as do flapping vibrations
Numerical Study of the Spin Hall Conductance in the Luttinger Model
We present first numerical studies of the disorder effect on the recently
proposed intrinsic spin Hall conductance in a three dimensional (3D) lattice
Luttinger model. The results show that the spin Hall conductance remains finite
in a wide range of disorder strength, with large fluctuations. The
disorder-configuration-averaged spin Hall conductance monotonically decreases
with the increase of disorder strength and vanishes before the Anderson
localization takes place. The finite-size effect is also discussed.Comment: 4 pages, 4 figures; the final version appearing in PR
Passive faraday mirror attack in practical two-way quantum key distribution system
The faraday mirror (FM) plays a very important role in maintaining the
stability of two way plug-and-play quantum key distribution (QKD) system.
However, the practical FM is imperfect, which will not only introduce
additional quantum bit error rate (QBER) but also leave a loophole for Eve to
spy the secret key. In this paper, we propose a passive faraday mirror attack
in two way QKD system based on the imperfection of FM. Our analysis shows that,
if the FM is imperfect, the dimension of Hilbert space spanned by the four
states sent by Alice is three instead of two. Thus Eve can distinguish these
states with a set of POVM operators belonging to three dimension space, which
will reduce the QBER induced by her attack. Furthermore, a relationship between
the degree of the imperfection of FM and the transmittance of the practical QKD
system is obtained. The results show that, the probability that Eve loads her
attack successfully depends on the degree of the imperfection of FM rapidly,
but the QBER induced by Eve's attack changes with the degree of the
imperfection of FM slightly
Disorder driven collapse of the mobility gap and transition to an insulator in fractional quantum Hall effect
We study the nu=1/3 quantum Hall state in presence of the random disorder. We
calculate the topologically invariant Chern number, which is the only quantity
known at present to unambiguously distinguish between insulating and current
carrying states in an interacting system. The mobility gap can be determined
numerically this way, which is found to agree with experimental value
semiquantitatively. As the disorder strength increases towards a critical
value, both the mobility gap and plateau width narrow continuously and
ultimately collapse leading to an insulating phase.Comment: 4 pages with 4 figure
- …