110,699 research outputs found
In Defense of the Epistemic Imperative
Sample (2015) argues that scientists ought not to believe that their theories are true because they cannot fulfill the epistemic obligation to take the diachronic perspective on their theories. I reply that Sample’s argument imposes an inordinately heavy epistemic obligation on scientists, and that it spells doom not only for scientific theories but also for observational beliefs and philosophical ideas that Samples endorses. I also delineate what I take to be a reasonable epistemic obligation for scientists. In sum, philosophers ought to impose on scientists only an epistemic standard that they are willing to impose on themselves
States near Dirac points of rectangular graphene dot in a magnetic field
In neutral graphene dots the Fermi level coincides with the Dirac points. We
have investigated in the presence of a magnetic field several unusual
properties of single electron states near the Fermi level of such a
rectangular-shaped graphene dot with two zigzag and two armchair edges. We find
that a quasi-degenerate level forms near zero energy and the number of states
in this level can be tuned by the magnetic field. The wavefunctions of states
in this level are all peaked on the zigzag edges with or without some weight
inside the dot. Some of these states are magnetic field-independent surface
states while the others are field-dependent. We have found a scaling result
from which the number of magnetic field-dependent states of large dots can be
inferred from those of smaller dots.Comment: Physical review B in pres
Muon anomalous magnetic moment from effective supersymmetry
We present a detailed analysis on the possible maximal value of the muon
(g-2) (= 2 a_mu) within the context of effective SUSY models with R parity
conservation. First of all, the mixing among the second and the third family
sleptons can contribute at one loop level to the a_mu(SUSY) and tau -> mu gamma
simultaneously. One finds that the a_mu(SUSY) can be as large as (10-20)*10^-10
for any tan beta, imposing the upper limit on the tau -> mu gamma branching
ratio. Furthermore, the two-loop Barr-Zee type contributions to a_mu(SUSY) can
be significant for large tan beta, if a stop is light and mu and A_t are large
enough (O(1) TeV). In this case, it is possible to have a_mu(SUSY) upto
O(10)*10^-10 without conflicting with tau -> l gamma. We conclude that the
possible maximal value for a_mu(SUSY) is about 20*10^-10 for any tan beta.
Therefore the BNL experiment on the muon a_mu can exclude the effective SUSY
models only if the measured deviation is larger than \sim 30*10^-10.Comment: 10 pages, 3 figure
Singlet portal extensions of the standard seesaw models to dark sector with local dark symmetry: An alternative to the new minimal standard model
Assuming dark matter is absolutely stable due to unbroken dark gauge symmetry
and singlet operators are portals to the dark sector, we present a simple
extension of the standard seesaw model that can accommodate all the
cosmological observations as well as terrestrial experiments available as of
now, including leptogenesis, extra dark radiation of (resulting in
the effective number of neutrino species), Higgs
inflation, small and large scale structure formation, and current relic density
of scalar DM (). The Higgs signal strength is equal to one as in the SM for
unbroken case with a scalar dark matter, but it could be less than one
independent of decay channels if the dark matter is a dark sector fermion or if
is spontaneously broken, because of a mixing with a new neutral scalar
boson in the models.Comment: Presented at the 9th PATRAS Workshop on Axions, WIMPs and WISP
Does Scientific Progress Consist in Increasing Knowledge or Understanding?
Bird argues that scientific progress consists in increasing knowledge. Dellsén objects that increasing knowledge is neither necessary nor sufficient for scientific progress, and argues that scientific progress rather consists in increasing understanding. Dellsén also contends that unlike Bird’s view, his view can account for the scientific practices of using idealizations and of choosing simple theories over complex ones. I argue that Dellsén’s criticisms against Bird’s view fail, and that increasing understanding cannot account for scientific progress, if acceptance, as opposed to belief, is required for scientific understanding
Effect of Defects on the Line shape of Electron Paramagnetic Resonance Signals from the Single-Molecule Magnet Mn12: A Theoretical Study
We herein estimate the effect of lattice defects on the line shape of
electron paramagnetic resonance (EPR) signals from a single crystal of the S=10
single-molecule magnet Mn with the external magnetic field along the
crystal c axis. A second-order perturbation treatment of an effective
single-spin Hamiltonian indicates that a small, random, static misorientation
of the magnetic symmetry axes in a crystalline lattice can lead to asymmetric
EPR peaks. Full spectra are simulated by calculating probability-distribution
functions for the resonant fields, employing distributions in the tilt angle of
the easy axis from the c axis, in the uniaxial anisotropy parameter, and in the
-factor. We discuss conditions under which the asymmetry in the EPR spectra
becomes prominent. The direction and magnitude of the asymmetry provide
information on the specific energy levels involved with the EPR transition, the
EPR frequency, and the distribution in the tilt angle.Comment: published versio
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