150 research outputs found
Imprints of Short Distance Physics On Inflationary Cosmology
We analyze the impact of certain modifications to short distance physics on
the inflationary perturbation spectrum. For the specific case of power-law
inflation, we find distinctive -- and possibly observable -- effects on the
spectrum of density perturbations.Comment: Revtex 4, 3 eps figs, 4 page
A generic estimate of trans-Planckian modifications to the primordial power spectrum in inflation
We derive a general expression for the power spectra of scalar and tensor
fluctuations generated during inflation given an arbitrary choice of boundary
condition for the mode function at a short distance. We assume that the
boundary condition is specified at a short-distance cutoff at a scale which
is independent of time. Using a particular prescription for the boundary
condition at momentum , we find that the modulation to the power spectra
of density and gravitational wave fluctuations is of order , where
is the Hubble parameter during inflation, and we argue that this behavior is
generic, although by no means inevitable. With fixed boundary condition, we
find that the shape of the modulation to the power spectra is determined
entirely by the deviation of the background spacetime from the de Sitter limit.Comment: 15 pages (RevTeX), 2 figure
Is null-point reconnection important for solar flux emergence?
The role of null-point reconnection in a 3D numerical MHD model of solar
emerging flux is investigated. The model consists of a twisted magnetic flux
tube rising through a stratified convection zone and atmosphere to interact and
reconnect with a horizontal overlying magnetic field in the atmosphere. Null
points appear as the reconnection begins and persist throughout the rest of the
emergence, where they can be found mostly in the model photosphere and
transition region, forming two loose clusters on either side of the emerging
flux tube. Up to 26 nulls are present at any one time, and tracking in time
shows that there is a total of 305 overall, despite the initial simplicity of
the magnetic field configuration. We find evidence for the reality of the nulls
in terms of their methods of creation and destruction, their balance of signs,
their long lifetimes, and their geometrical stability. We then show that due to
the low parallel electric fields associated with the nulls, null-point
reconnection is not the main type of magnetic reconnection involved in the
interaction of the newly emerged flux with the overlying field. However, the
large number of nulls implies that the topological structure of the magnetic
field must be very complex and the importance of reconnection along separators
or separatrix surfaces for flux emergence cannot be ruled out.Comment: 26 pages, 12 figures. Added one referenc
Magnetic trapping of ultracold neutrons
Three-dimensional magnetic confinement of neutrons is reported. Neutrons are
loaded into an Ioffe-type superconducting magnetic trap through inelastic
scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low
energy and in the appropriate spin state are confined by the magnetic field
until they decay. The electron resulting from neutron decay produces
scintillations in the liquid helium bath that results in a pulse of extreme
ultraviolet light. This light is frequency downconverted to the visible and
detected. Results are presented in which 500 +/- 155 neutrons are magnetically
trapped in each loading cycle, consistent with theoretical predictions. The
lifetime of the observed signal, 660 s +290/-170 s, is consistent with the
neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review
Evidence for a narrow dip structure at 1.9 GeV/c in diffractive photoproduction
A narrow dip structure has been observed at 1.9 GeV/c in a study of
diffractive photoproduction of the final state performed by the
Fermilab experiment E687.Comment: The data of Figure 6 can be obtained by downloading the raw data file
e687_6pi.txt. v5 (2nov2018): added Fig. 7, the 6 pion energy distribution as
requested by a reade
Proximity effect at superconducting Sn-Bi2Se3 interface
We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions
down to 250 mK and in different magnetic fields. A number of conductance
anomalies were observed below the superconducting transition temperature of Sn,
including a small gap different from that of Sn, and a zero-bias conductance
peak growing up at lower temperatures. We discussed the possible origins of the
smaller gap and the zero-bias conductance peak. These phenomena support that a
proximity-effect-induced chiral superconducting phase is formed at the
interface between the superconducting Sn and the strong spin-orbit coupling
material Bi2Se3.Comment: 7 pages, 8 figure
Centrality Dependence of the High p_T Charged Hadron Suppression in Au+Au collisions at sqrt(s_NN) = 130 GeV
PHENIX has measured the centrality dependence of charged hadron p_T spectra
from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T
decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction
of the contribution from hard scattering to high p_T hadron production. For
central collisions the yield at high p_T is shown to be suppressed compared to
binary nucleon-nucleon collision scaling of p+p data. This suppression is
monotonically increasing with centrality, but most of the change occurs below
30% centrality, i.e. for collisions with less than about 140 participating
nucleons. The observed p_T and centrality dependence is consistent with the
particle production predicted by models including hard scattering and
subsequent energy loss of the scattered partons in the dense matter created in
the collisions.Comment: 7 pages text, LaTeX, 6 figures, 2 tables, 307 authors, resubmitted to
Phys. Lett. B. Revised to address referee concerns. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
The statistics of string/M theory vacua
We discuss systematic approaches to the classification of string/M theory
vacua, and physical questions this might help us resolve. To this end, we
initiate the study of ensembles of effective Lagrangians, which can be used to
precisely study the predictive power of string theory, and in simple examples
can lead to universality results. Using these ideas, we outline an approach to
estimating the number of vacua of string/M theory which can realize the
Standard Model.Comment: harvmac, 72pp (v4: fixed error in discussion of quiver ensembles
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