Confinement and scaling in deep inelastic scattering

We show that parton confinement in the final state generates large $1/Q^2$ corrections to Bjorken scaling, thus leaving less room for the logarithmic corrections. In particular, the $x$-scaling violations at large $x$ are entirely described in terms of power corrections. For treatment of these non-perturbative effects, we derive a new expansion in powers of $1/Q^2$ for the structure function that is free of infra-red singularities and which reduces corrections to the leading term. The leading term represents scattering from an off-mass-shell parton, which keeps the same virtual mass in the final state. It is found that this quasi-free term is a function of a new variable $\bar x$, which coincides with the Bjorken variable $x$ for $Q^2\to\infty$. The two variables are very different, however, at finite $Q^2$. In particular, the variable $\bar x$ depends on the invariant mass of the spectator particles. Analysis of the data at large $x$ shows excellent scaling in the variable $\bar x$, and determines the value of the diquark mass to be close to zero. $\bar x$-scaling allows us to extract the structure function near the elastic threshold. It is found to behave as $F_2\sim (1-x)^{3.7}$. Predictions for the structure functions based on $\bar x$-scaling are made.Comment: Discussion of target mass corrections is added. Accepted for publication in Phys. Rev.

Arc expression identifies the lateral amygdala fear memory trace

Memories are encoded within sparsely distributed neuronal ensembles. However, the defining cellular properties of neurons within a memory trace remain incompletely understood. Using a fluorescence-based Arc reporter, we were able to visually identify the distinct subset of lateral amygdala (LA) neurons activated during auditory fear conditioning. We found that Arc-expressing neurons have enhanced intrinsic excitability and are preferentially recruited into newly encoded memory traces. Furthermore, synaptic potentiation of thalamic inputs to the LA during fear conditioning is learning-specific, postsynaptically mediated and highly localized to Arc-expressing neurons. Taken together, our findings validate the immediate-early gene Arc as a molecular marker for the LA neuronal ensemble recruited during fear learning. Moreover, these results establish a model of fear memory formation in which intrinsic excitability determines neuronal selection, whereas learning-related encoding is governed by synaptic plasticity

Structure function of a damped harmonic oscillator

Following the Caldeira-Leggett approach to describe dissipative quantum systems the structure function for a harmonic oscillator with Ohmic dissipation is evaluated by an analytic continuation from euclidean to real time. The analytic properties of the Fourier transform of the structure function with respect to the energy transfer (the ``characteristic function'') are studied and utilized. In the one-parameter model of Ohmic dissipation we show explicitly that the broadening of excited states increases with the state number without violating sum rules. Analytic and numerical results suggest that this is a phenomenologically relevant, consistent model to include the coupling of a single (sub-)nuclear particle to unobserved and complex degrees of freedom.Comment: 23 pages, 5 figures, RevTex4, minor changes following referee's comments and by PRC: the definite article in the original title has been droppe

Role of the Delta (1232) in DIS on polarized 3^3He and extraction of the neutron spin structure function g1n(x,Q2)g_{1}^{n}(x,Q^2)

We consider the effect of the transitions $n \to \Delta^{0}$ and $p \to \Delta^{+}$ in deep inelastic scattering on polarized $^3$He on the extraction of the neutron spin structure function $g_{1}^{n}(x,Q^2)$. Making the natural assumption that these transitions are the dominant non-nucleonic contributions to the renormalization of the axial vector coupling constant in the A=3 system, we find that the effect of $\Delta$ increases $g_{1}^{n}(x,Q^2)$ by $10 \div 40$% in the range $0.05 \le x \le 0.6$, where our considerations are applicable and most of the data for $g_{1}^{n}(x,Q^2)$ exist.Comment: 23 pages, 6 figures, revte

Mechanisms underlying cognitive deficits in a mouse model for Costello Syndrome are distinct from other RASopathy mouse models

RASopathies, characterized by germline mutations in genes encoding proteins of the RAS-ERK signaling pathway, show overlapping phenotypes, which manifest themselves with a varying severity of intellectual disability. However, it is unclear to what extent they share the same downstream pathophysiology that underlies the cognitive deficits. Costello syndrome (CS) is a rare RASopathy caused by activating mutations in the HRAS gene. Here we investigated the mechanisms underlying the cognitive deficits of HRas G12V/G12V mice. HRas G12V/G12V mice showed robust upregulation of ERK signaling, neuronal hypertrophy, increased brain volume, spatial learning deficits, and impaired mGluR-dependent long-term depression (LTD). In contrast, long-term potentiation (LTP), which is affected in other RASopathy mouse models was unaffected. Treatment with lovastatin, a HMG-CoA-Reductase inhibitor which has been shown to rescue the behavioral phenotypes of mouse models of NF1 and Noonan syndrome, was unable to restore ERK signaling and the cognitive deficits of HRas G12V/G12V mice. Administration of a potent mitogen-activated protein kinase (MEK) inhibitor rescued the ERK upregulation and the mGluR-LTD deficit of HRas G12V/G12V mice, but failed to rescue the cognitive deficits. Taken together, this study indicates that the fundamental molecular and cellular mechanisms underlying the cognitive aspects of different RASopathies are remarkably distinct, and may require disease specific treatments

Open string modes at brane intersections

We study systematically the open string modes of a general class of BPS intersections of branes. We work in the approximation in which one of the branes is considered as a probe embedded in the near-horizon geometry generated by the other type of branes. We mostly concentrate on the D3-D5 and D3-D3 intersections, which are dual to defect theories with a massive hypermultiplet confined to the defect. In these cases we are able to obtain analytical expressions for the fluctuation modes of the probe and to compute the corresponding mass spectra of the dual operators in closed form. Other BPS intersections are also studied and their fluctuation modes and spectra are found numerically.Comment: 58 pages, 3 figures, LaTeX;v2: typos correcte

Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon

There are two mechanisms for the generation of an asymmetry between the strange and anti-strange quark distributions in the nucleon: nonperturbative contributions originating from nucleons fluctuating into virtual baryon-meson pairs such as $\Lambda K$ and $\Sigma K$, and perturbative contributions arising from gluons splitting into strange and anti-strange quark pairs. While the nonperturbative contributions are dominant in the large-$x$ region, the perturbative contributions are more significant in the small-$x$ region. We calculate this asymmetry taking into account both nonperturbative and perturbative contributions, thus giving a more accurate evaluation of this asymmetry over the whole domain of $x$. We find that the perturbative contributions are generally a few times larger in magnitude than the nonperturbative contributions, which suggests that the best region to detect this asymmetry experimentally is in the region $0.02 < x < 0.03$. We find that the asymmetry may have more than one node, which is an effect that should be taken into account, e.g. for parameterizations of the strange and anti-strange quark distributions used in global analysis of parton distributions.Comment: 14 pages, 4 figures, figures comparing theoretical calculations with NNPDF global analysis added, accepted for publication in EPJ

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc