84,972 research outputs found

### QCD Chiral restoration at finite $T$ under the Magnetic field: Studies based on the instanton vacuum model

We investigate the chiral restoration at finite temperature $(T)$ under the
strong external magnetic field $\vec{B}=B_{0}\hat{z}$ of the SU(2) light-flavor
QCD matter. We employ the instanton-liquid QCD vacuum configuration accompanied
with the linear Schwinger method for inducing the magnetic field. The
Harrington-Shepard caloron solution is used to modify the instanton parameters,
i.e. the average instanton size $(\bar{\rho})$ and inter-instanton distance
$(\bar{R})$, as functions of $T$. In addition, we include the meson-loop
corrections (MLC) as the large-$N_{c}$ corrections because they are critical
for reproducing the universal chiral restoration pattern. We present the
numerical results for the constituent-quark mass as well as chiral condensate
which signal the spontaneous breakdown of chiral-symmetry (SB$\chi$S), as
functions of $T$ and $B$. Besides we find that the changes for the $F_\pi$ and
$m_\pi$ due to the magnetic field is relatively small, in comparison to those
caused by the finite $T$ effect.Comment: 4 pages, 1 table, 6figs. arXiv admin note: significant text overlap
with arXiv:1103.605

### Casimir Force in Compact Noncommutative Extra Dimensions and Radius Stabilization

We compute the one loop Casimir energy of an interacting scalar field in a
compact noncommutative space of $R^{1,d}\times T^2_\theta$, where we have
ordinary flat $1+d$ dimensional Minkowski space and two dimensional
noncommuative torus. We find that next order correction due to the
noncommutativity still contributes an attractive force and thus will have a
quantum instability. However, the case of vector field in a periodic boundary
condition gives repulsive force for $d>5$ and we expect a stabilized radius.
This suggests a stabilization mechanism for a senario in Kaluza-Klein theory,
where some of the extra dimensions are noncommutative.Comment: 10 pages, TeX, harvma

### Organic Selection and Social Heredity: The Original Baldwin Effect Revisited

The so-called “Baldwin Effect” has been studied for years
in the fields of Artificial Life, Cognitive Science, and Evolutionary
Theory across disciplines. This idea is often conflated
with genetic assimilation, and has raised controversy
in trans-disciplinary scientific discourse due to the many interpretations
it has. This paper revisits the “Baldwin Effect”
in Baldwin’s original spirit from a joint historical, theoretical
and experimental approach. Social Heredity – the inheritance
of cultural knowledge via non-genetic means in Baldwin’s
term – is also taken into consideration. I shall argue that the
Baldwin Effect can occur via social heredity without necessity
for genetic assimilation. Computational experiments are
carried out to show that when social heredity is permitted with
high fidelity, there is no need for the assimilation of acquired
characteristics; instead the Baldwin Effect occurs as promoting
more plasticity to facilitate future intelligence. The role
of mind and intelligence in evolution and its implications in
an extended synthesis of evolution are briefly discussed

### On the High-SNR Capacity of the Gaussian Interference Channel and New Capacity Bounds

The best outer bound on the capacity region of the two-user Gaussian
Interference Channel (GIC) is known to be the intersection of regions of
various bounds including genie-aided outer bounds, in which a genie provides
noisy input signals to the intended receiver. The Han and Kobayashi (HK) scheme
provides the best known inner bound. The rate difference between the best known
lower and upper bounds on the sum capacity remains as large as 1 bit per
channel use especially around $g^2=P^{-1/3}$, where $P$ is the symmetric power
constraint and $g$ is the symmetric real cross-channel coefficient. In this
paper, we pay attention to the \emph{moderate interference regime} where
$g^2\in (\max(0.086, P^{-1/3}),1)$. We propose a new upper-bounding technique
that utilizes noisy observation of interfering signals as genie signals and
applies time sharing to the genie signals at the receivers. A conditional
version of the worst additive noise lemma is also introduced to derive new
capacity bounds. The resulting upper (outer) bounds on the sum capacity
(capacity region) are shown to be tighter than the existing bounds in a certain
range of the moderate interference regime. Using the new upper bounds and the
HK lower bound, we show that $R_\text{sym}^*=\frac{1}{2}\log
\big(|g|P+|g|^{-1}(P+1)\big)$ characterizes the capacity of the symmetric real
GIC to within $0.104$ bit per channel use in the moderate interference regime
at any signal-to-noise ratio (SNR). We further establish a high-SNR
characterization of the symmetric real GIC, where the proposed upper bound is
at most $0.1$ bit far from a certain HK achievable scheme with Gaussian
signaling and time sharing for $g^2\in (0,1]$. In particular, $R_\text{sym}^*$
is achievable at high SNR by the proposed HK scheme and turns out to be the
high-SNR capacity at least at $g^2=0.25, 0.5$.Comment: Submitted to IEEE Transactions on Information Theory on June 2015,
revised on November 2016, and accepted for publication on Feb. 28, 201

### Capacity Bounds for the $K$-User Gaussian Interference Channel

The capacity region of the $K$-user Gaussian interference channel (GIC) is a
long-standing open problem and even capacity outer bounds are little known in
general. A significant progress on degrees-of-freedom (DoF) analysis, a
first-order capacity approximation, for the $K$-user GIC has provided new
important insights into the problem of interest in the high signal-to-noise
ratio (SNR) limit. However, such capacity approximation has been observed to
have some limitations in predicting the capacity at \emph{finite} SNR. In this
work, we develop a new upper-bounding technique that utilizes a new type of
genie signal and applies \emph{time sharing} to genie signals at $K$ receivers.
Based on this technique, we derive new upper bounds on the sum capacity of the
three-user GIC with constant, complex channel coefficients and then generalize
to the $K$-user case to better understand sum-rate behavior at finite SNR. We
also provide closed-form expressions of our upper bounds on the capacity of the
$K$-user symmetric GIC easily computable for \emph{any} $K$. From the
perspectives of our results, some sum-rate behavior at finite SNR is in line
with the insights given by the known DoF results, while some others are not. In
particular, the well-known $K/2$ DoF achievable for almost all constant real
channel coefficients turns out to be not embodied as a substantial performance
gain over a certain range of the cross-channel coefficient in the $K$-user
symmetric real case especially for \emph{large} $K$. We further investigate the
impact of phase offset between the direct-channel coefficient and the
cross-channel coefficients on the sum-rate upper bound for the three-user
\emph{complex} GIC. As a consequence, we aim to provide new findings that could
not be predicted by the prior works on DoF of GICs.Comment: Presented in part at ISIT 2015, submitted to IEEE Transactions on
Information Theory on July 2015, and revised on January 201

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