Altered expression of Alzheimer's disease-related proteins in male hypogonadal mice

Age-related depletion of estrogens and androgens is associated with an increase in Alzheimer's disease (AD) brain pathology and diminished cognitive function. Here we investigated AD-associated molecular and cellular changes in brains of aged hypogonadal (hpg) male and female mice. hpg Mice have a spontaneous, inactivating genetic mutation in the GnRH gene resulting in lifelong deficiency of gonadotropins and gonadal sex hormones. Western blot analysis revealed low levels of amyloid precursor protein and high levels of presenilin 1, amyloid precursor protein C-terminal fragment, and beta-amyloid 42 in brains of aged male, but not female, hpg mice. Changes were confined to the hippocampus and were not evident in the cerebellum or other brain tissues. Male hpg mice tended to have lower levels of IL-1 beta protein than male littermate controls. Immunohistochemical staining of the basal forebrain revealed that male hpg mice had lower choline acetyltransferase levels per neuron compared with controls. These AD-like changes specific to male hpg mice supports a link between androgen depletion and the development of AD pathology

Dissolving D0-brane into D2-brane with background B-field

D0-branes on a D2-brane with a constant background B-field are unstable due to the presence of a tachyonic mode and expected to dissolve into the D2-brane to formulate a constant D0-charge density. In this paper we study such a dissolution process in terms of a noncommutative gauge theory. Our results show that the localized D0-brane spreads out over all of space on the D2-brane as the tachyon rolls down into a stable vacuum. D0-branes on a D2-brane can be described as unstable solitons in a noncommutative gauge theory in 2+1 dimensions in the Seiberg-Witten limit. In contrast to the case of annihilation of a non-BPS D-brane, we are free from difficulty of disappearance of DOF, since there exist open strings after the tachyon condensation. We solve an equation of motion of the gauge field numerically, and our results show that the localized soliton smears over all of noncommutative space. In addition, we evaluate distributions of D-brane charge, F-string charge, and energy density via formulas derived in Matrix theory. Our results show that the initial singularities of D0-charge and energy density are resolved by turning on the tachyon, and they disperse over the whole space on the D2-brane during the tachyon condensation process.Comment: 42 pages, 20 figures, JHEP style; references added, clarifications added in section 3.1; references adde

Non-Commutative Instantons and the Seiberg-Witten Map

We present several results concerning non-commutative instantons and the Seiberg-Witten map. Using a simple ansatz we find a large new class of instanton solutions in arbitrary even dimensional non-commutative Yang-Mills theory. These include the two dimensional ``shift operator'' solutions and the four dimensional Nekrasov-Schwarz instantons as special cases. We also study how the Seiberg-Witten map acts on these instanton solutions. The infinitesimal Seiberg-Witten map is shown to take a very simple form in operator language, and this result is used to give a commutative description of non-commutative instantons. The instanton is found to be singular in commutative variables.Comment: 26 pages, AMS-LaTeX. v2: the formula for the commutative description of the Nekrasov-Schwarz instanton corrected (sec. 4). v3: minor correction

Localized Tachyons and the g_cl conjecture

We consider C/Z_N and C^2/Z_N orbifolds of heterotic string theories and Z_N orbifolds of AdS_3. We study theories with N=2 worldsheet superconformal invariance and construct RG flows. Following Harvey, Kutasov, Martinec and Moore, we compute g_cl and show that it decreases monotonically along RG flows- as conjectured by them. For the heterotic string theories, the gauge degrees of freedom do not contribute to the computation of g_cl.Comment: Corrections and clarifications made, 19 page

Open String Star as a Continuous Moyal Product

We establish that the open string star product in the zero momentum sector can be described as a continuous tensor product of mutually commuting two dimensional Moyal star products. Let the continuous variable $\kappa \in [~0,\infty)$ parametrize the eigenvalues of the Neumann matrices; then the noncommutativity parameter is given by $\theta(\kappa) =2\tanh(\pi\kappa/4)$. For each $\kappa$, the Moyal coordinates are a linear combination of even position modes, and the Fourier transform of a linear combination of odd position modes. The commuting coordinate at $\kappa=0$ is identified as the momentum carried by half the string. We discuss the relation to Bars' work, and attempt to write the string field action as a noncommutative field theory.Comment: 30 pages, LaTeX. One reference adde

Puffed Noncommutative Nonabelian Vortices

We present new solutions of noncommutative gauge theories in which coincident unstable vortices expand into unstable circular shells. As the theories are noncommutative, the naive definition of the locations of the vortices and shells is gauge-dependent, and so we define and calculate the profiles of these solutions using the gauge-invariant noncommutative Wilson lines introduced by Gross and Nekrasov. We find that charge 2 vortex solutions are characterized by two positions and a single nonnegative real number, which we demonstrate is the radius of the shell. We find that the radius is identically zero in all 2-dimensional solutions. If one considers solutions that depend on an additional commutative direction, then there are time-dependent solutions in which the radius oscillates, resembling a braneworld description of a cyclic universe. There are also smooth BIon-like space-dependent solutions in which the shell expands to infinity, describing a vortex ending on a domain wall.Comment: 21 pages, 3 eps figures. v2: published version, analytic solution adde

Non-BPS Solutions of the Noncommutative CP^1 Model in 2+1 Dimensions

We find non-BPS solutions of the noncommutative CP^1 model in 2+1 dimensions. These solutions correspond to soliton anti-soliton configurations. We show that the one-soliton one-anti-soliton solution is unstable when the distance between the soliton and the anti-soliton is small. We also construct time-dependent solutions and other types of solutions.Comment: 11 pages, minor correction

Unstable solitons on noncommutative tori and D-branes

We describe a class of exact solutions of super Yang-Mills theory on even-dimensional noncommutative tori. These solutions generalize the solitons on a noncommutative plane introduced in hep-th/0009142 that are conjectured to describe unstable D2p-D0 systems. We show that the spectrum of quadratic fluctuations around our solutions correctly reproduces the string spectrum of the D2p-D0 system in the Seiberg-Witten decoupling limit. In particular the fluctuations correctly reproduce the 0-0 string winding modes. For p=1 and p=2 we match the differences between the soliton energy and the energy of an appropriate SYM BPS state with the binding energies of D2-D0 and D4-D0 systems. We also give an example of a soliton that we conjecture describes branes of intermediate dimension on a torus such as a D2-D4 system on a four-torus.Comment: 22 pages, Latex; v.2: references adde

Comments on Noncommutative Sigma Models

We review the derivation of a noncommutative version of the nonlinear sigma model on \CPn and it's soliton solutions for finite $\theta$ emphasizing the similarities it bears to the GMS scalar field theory. It is also shown that unlike the scalar theory, some care needs to be taken in defining the topological charge of BPS solitons of the theory due to nonvanishing surface terms in the energy functional. Finally it is shown that, like its commutative analogue, the noncommutative \CPn-model also exhibits a non-BPS sector. Unlike the commutative case however, there are some surprises in the noncommutative case that merit further study.Comment: 22 pages, 4 figures, LaTeX (JHEP3), Minor changes, Discussion expanded and references adde

Dualities, Twists, and Gauge Theories with Non-Constant Non-Commutativity

We study the world volume theory of D3-branes wrapping the Melvin universe supported by background NSNS B-field. In the appropriate decoupling limit, the open string dynamics is that of non-commutative guage field theory with non-constant non-commutativity. We identify this model as a simple Melvin twist of flat D3 branes. Along similar lines, one recognizes the model of Hashimoto and Sethi as being the Melvin null twist, and the model of Dolan and Nappi as being the null Melvin twist, of the flat D3-brane. This construction therefore offers a unified perspective on most of the known explicit constructions of non-commutative gauge theories as a decoupled theory of D-branes in a B-field background. We also describe the world volume theory on the D3-brane in Melvin universe which is decaying via the nucleation of monopole anti-monopole pair.Comment: 18 pages, 1 figure, References added, typo correcte