84,972 research outputs found

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

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    We investigate the chiral restoration at finite temperature (T)(T) under the strong external magnetic field B=B0z^\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 (ρˉ)(\bar{\rho}) and inter-instanton distance (Rˉ)(\bar{R}), as functions of TT. In addition, we include the meson-loop corrections (MLC) as the large-NcN_{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 (SBχ\chiS), as functions of TT and BB. Besides we find that the changes for the FπF_\pi and mπm_\pi due to the magnetic field is relatively small, in comparison to those caused by the finite TT 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

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    We compute the one loop Casimir energy of an interacting scalar field in a compact noncommutative space of R1,d×Tθ2R^{1,d}\times T^2_\theta, where we have ordinary flat 1+d1+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>5d>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

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    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

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    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 g2=P1/3g^2=P^{-1/3}, where PP is the symmetric power constraint and gg is the symmetric real cross-channel coefficient. In this paper, we pay attention to the \emph{moderate interference regime} where g2(max(0.086,P1/3),1)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 Rsym=12log(gP+g1(P+1))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 0.1040.104 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 0.10.1 bit far from a certain HK achievable scheme with Gaussian signaling and time sharing for g2(0,1]g^2\in (0,1]. In particular, RsymR_\text{sym}^* is achievable at high SNR by the proposed HK scheme and turns out to be the high-SNR capacity at least at g2=0.25,0.5g^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 KK-User Gaussian Interference Channel

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    The capacity region of the KK-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 KK-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 KK 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 KK-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 KK-user symmetric GIC easily computable for \emph{any} KK. 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/2K/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 KK-user symmetric real case especially for \emph{large} KK. 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