10,506 research outputs found

### Study of Scalar Mesons and Related Radiative Decays

After a brief review of the puzzling light scalar meson sector of QCD, a
brief summary will be given of a paper concerning radiative decays involving
the light scalars. There, a simple vector meson dominance model is constructed
in an initial attempt to relate a large number of the radiative decays
involving a putative scalar nonet to each other. As an application it is
illustrated why $a_0(980)-f_0(980)$ mixing is not expected to greatly alter the
$f_0/a_0$ production ratio for radiative $\phi$ decays.Comment: 9 pages, 3 figures, Talk presented at SUNYIT (Utica/NY) conference on
High Energy Physics, June 6, 200

### Classification of generalized Hadamard matrices H(6,3) and quaternary Hermitian self-dual codes of length 18

All generalized Hadamard matrices of order 18 over a group of order 3,
H(6,3), are enumerated in two different ways: once, as class regular symmetric
(6,3)-nets, or symmetric transversal designs on 54 points and 54 blocks with a
group of order 3 acting semi-regularly on points and blocks, and secondly, as
collections of full weight vectors in quaternary Hermitian self-dual codes of
length 18. The second enumeration is based on the classification of Hermitian
self-dual [18,9] codes over GF(4), completed in this paper. It is shown that up
to monomial equivalence, there are 85 generalized Hadamard matrices H(6,3), and
245 inequivalent Hermitian self-dual codes of length 18 over GF(4).Comment: 17 pages. Minor revisio

### Is there a black hole minimum mass?

Applying the first and generalised second laws of thermodynamics for a
realistic process of near critical black hole formation, we derive an entropy
bound, which is identical to Bekenstein's one for radiation. Relying upon this
bound, we derive an absolute minimum mass $\sim0.04 \sqrt{g_{*}}m_{\rm Pl}$,
where $g_{*}$ and $m_{\rm Pl}$ is the effective degrees of freedom for the
initial temparature and the Planck mass, respectively. Since this minimum mass
coincides with the lower bound on masses of which black holes can be regarded
as classical against the Hawking evaporation, the thermodynamical argument will
not prohibit the formation of the smallest classical black hole. For more
general situations, we derive a minimum mass, which may depend on the initial
value for entropy per particle. For primordial black holes, however, we show
that this minimum mass can not be much greater than the Planck mass at any
formation epoch of the Universe, as long as $g_{*}$ is within a reasonable
range. We also derive a size-independent upper bound on the entropy density of
a stiff fluid in terms of the energy density.Comment: 4 pages, accepted for publication in Physical Review D, minor
correctio

### Coarse-grained loop algorithms for Monte Carlo simulation of quantum spin systems

Recently, Syljuasen and Sandvik proposed a new framework for constructing
algorithms of quantum Monte Carlo simulation. While it includes new classes of
powerful algorithms, it is not straightforward to find an efficient algorithm
for a given model. Based on their framework, we propose an algorithm that is a
natural extension of the conventional loop algorithm with the split-spin
representation. A complete table of the vertex density and the worm-scattering
probability is presented for the general XXZ model of an arbitrary S with a
uniform magnetic field.Comment: 12 pages, 7 figures, insert a word "squared" in the first line of the
caption of Fig.7 and correct the label of vertical axis of Fig.

### Fate of Vector Dominance in the Effective Field Theory

We reveal the full phase structure of the effective field theory for QCD,
based on the hidden local symmetry (HLS) through the one-loop renormalization
group equation including quadratic divergences. We then show that vector
dominance (VD) is not a sacred discipline of the effective field theory but
rather an accidental phenomenon peculiar to three-flavored QCD. In particular,
the chiral symmetry restoration in HLS model takes place in a wide phase
boundary surface, on which the VD is realized nowhere. This suggests that VD
may not be valid for chiral symmetry restoration in hot and/or dense QCD.Comment: 4 pages, 3 figures. One reference added. Minor modification to
shorten the manuscript. This is the version to appear in Physical Review
Letter

### Extended Technicolor Models with Two ETC Groups

We construct extended technicolor (ETC) models that can produce the large
splitting between the masses of the $t$ and $b$ quarks without necessarily
excessive contributions to the $\rho$ parameter or to neutral flavor-changing
processes. These models make use of two different ETC gauge groups, such that
left- and right-handed components of charge $Q=2/3$ quarks transform under the
same ETC group, while left- and right-handed components of charge -1/3 quarks
and charged leptons transform under different ETC groups. The models thereby
suppress the masses $m_b$ and $m_\tau$ relative to $m_t$, and $m_s$ and $m_\mu$
relative to $m_c$ because the masses of the $Q=-1/3$ quarks and charged leptons
require mixing between the two ETC groups, while the masses of the $Q=2/3$
quarks do not. A related source of the differences between these mass
splittings is the effect of the two hierarchies of breaking scales of the two
ETC groups. We analyze a particular model of this type in some detail. Although
we find that this model tends to suppress the masses of the first two
generations of down-type quarks and charged leptons too much, it gives useful
insights into the properties of theories with more than one ETC group.Comment: 14 pages, 4 figure

### Growth of primordial black holes in a universe containing a massless scalar field

The evolution of primordial black holes in a flat Friedmann universe with a
massless scalar field is investigated in fully general relativistic numerical
relativity. A primordial black hole is expected to form with a scale comparable
to the cosmological apparent horizon, in which case it may go through an
initial phase with significant accretion. However, if it is very close to the
cosmological apparent horizon size, the accretion is suppressed due to general
relativistic effects. In any case, it soon gets smaller than the cosmological
horizon and thereafter it can be approximated as an isolated vacuum solution
with decaying mass accretion. In this situation the dynamical and inhomogeneous
scalar field is typically equivalent to a perfect fluid with a stiff equation
of state $p=\rho$. The black hole mass never increases by more than a factor of
two, despite recent claims that primordial black holes might grow substantially
through accreting quintessence. It is found that the gravitational memory
scenario, proposed for primordial black holes in Brans-Dicke and scalar-tensor
theories of gravity, is highly unphysical.Comment: 24 pages, accepted for publication in Physical Review

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