579 research outputs found
Heterotic Matrix String Theory and Riemann Surfaces
We extend the results found for Matrix String Theory to Heterotic Matrix
String Theory, i.e. to a 2d O(N) SYM theory with chiral (anomaly free) matter
and N=(8,0) supersymmetry. We write down the instanton equations for this
theory and solve them explicitly. The solutions are characterized by branched
coverings of the basis cylinder, i.e. by compact Riemann surfaces with
punctures. We show that in the strong coupling limit the action becomes the
heterotic string action plus a free Maxwell action. Moreover the amplitude
based on a Riemann surface with p punctures and h handles is proportional to
g^{2-2h-p}, as expected for the heterotic string interaction theory with string
coupling g_s=1/g.Comment: 17 pages, JHEP LaTeX style, sentence delete
New physics in \epsilon' from chromomagnetic contributions and limits on Left-Right symmetry
New physics in the chromomagnetic flavor changing transition s->dg* can avoid
the strong GIM suppression of the Standard Model and lead to large
contributions to CP-violating observables, in particular to the epsilon'
parameter, that we address here. We discuss the case of the Left-Right
symmetric models, where this contribution implies bounds on the phases of the
right-handed quark mixing matrix, or in generic models with large phases a
strong bound on the Left-Right symmetry scale. To the leading order, a numeric
formula for epsilon' as a function of the short-distance coefficients for a
wide class of models of new physics is given.Comment: 12 pages, Eq. 12 and related numerics amende
Gravity-Yang-Mills-Higgs unification by enlarging the gauge group
We revisit an old idea that gravity can be unified with Yang-Mills theory by
enlarging the gauge group of gravity formulated as gauge theory. Our starting
point is an action that describes a generally covariant gauge theory for a
group G. The Minkowski background breaks the gauge group by selecting in it a
preferred gravitational SU(2) subgroup. We expand the action around this
background and find the spectrum of linearized theory to consist of the usual
gravitons plus Yang-Mills fields charged under the centralizer of the SU(2) in
G. In addition, there is a set of Higgs fields that are charged both under the
gravitational and Yang-Mills subgroups. These fields are generically massive
and interact with both gravity and Yang-Mills sector in the standard way. The
arising interaction of the Yang-Mills sector with gravity is also standard.
Parameters such as the Yang-Mills coupling constant and Higgs mass arise from
the potential function defining the theory. Both are realistic in the sense
explained in the paper.Comment: 61 pages, no figures (v2) some typos correcte
Pearson's random walk in the space of the CMB phases: evidence for parity asymmetry
The temperature fluctuations of the Cosmic Microwave Background (CMB) are
supposed to be distributed randomly in both magnitude and phase, following to
the simplest model of inflation. In this paper, we look at the odd and even
multipoles of the spherical harmonic decomposition of the CMB, and the
different characteristics of these, giving rise to a parity asymmetry. We
compare the even and odd multipoles in the CMB power spectrum, and also the
even and odd mean angles. We find for the multipoles of the power spectrum,
that there is power excess in odd multipoles, compared to even ones, meaning
that we have a parity asymmetry. Further, for the phases, we present a random
walk for the mean angles, and find a significant separation for even/odd mean
angles, especially so for galactic coordinates. This is further tested and
confirmed with a directional parity test, comparing the parity asymmetry in
galactic and ecliptic coordinates.Comment: Accepted for publication in Phys. Rev. D, 10 pages, 10 figures, 1
table. Some typographical errors corrected, and further references adde
Matrix String Theory and its Moduli Space
The correspondence between Matrix String Theory in the strong coupling limit
and IIA superstring theory can be shown by means of the instanton solutions of
the former. We construct the general instanton solutions of Matrix String
Theory which interpolate between given initial and final string configurations.
Each instanton is characterized by a Riemann surface of genus h with n
punctures, which is realized as a plane curve. We study the moduli space of
such plane curves and find out that, at finite N, it is a discretized version
of the moduli space of Riemann surfaces: instead of 3h-3+n its complex
dimensions are 2h-3+n, the remaining h dimensions being discrete. It turns out
that as tends to infinity, these discrete dimensions become continuous, and
one recovers the full moduli space of string interaction theory.Comment: 30 pages, LaTeX, JHEP.cls class file, minor correction
Large Fluctuations in Locational Marginal Prices
This paper investigates large fluctuations of Locational Marginal Prices (LMPs) in wholesale energy markets caused by volatile renewable generation profiles. Specifically, we study events of the form â(LMPââni=1[αâi,α+i]), where LMP is the vector of LMPs at the n power grid nodes, and αâ,α+âân are vectors of price thresholds specifying undesirable price occurrences. By exploiting the structure of the supply-demand matching mechanism in power grids, we look at LMPs as deterministic piecewise affine, possibly discontinuous functions of the stochastic input process, modeling uncontrollable renewable generation. We utilize techniques from large deviations theory to identify the most likely ways for extreme price spikes to happen, and to rank the nodes of the power grid in terms of their likelihood of experiencing a price spike. Our results are derived in the case of Gaussian fluctuations and are validated numerically on the IEEE 14-bus test case
Type 2 diabetes and reduced exercise tolerance: A review of the literature through an integrated physiology approach
The association between type 2 diabetes mellitus (T2DM) and heart failure (HF) is well established. Early in the course of the diabetic disease, some degree of impaired exercise capacity (a powerful marker of health status with prognostic value) can be frequently highlighted in otherwise asymptomatic T2DM subjects. However, the literature is quite heterogeneous, and the underlying pathophysiologic mechanisms are far from clear. Imaging-cardiopulmonary exercise testing (CPET) is a non-invasive, provocative test providing a multi-variable assessment of pulmonary, cardiovascular, muscular, and cellular oxidative systems during exercise, capable of offering unique integrated pathophysiological information. With this review we aimed at defying the cardiorespiratory alterations revealed through imaging-CPET that appear specific of T2DM subjects without overt cardiovascular or pulmonary disease. In synthesis, there is compelling evidence indicating a reduction of peak workload, peak oxygen assumption, oxygen pulse, as well as ventilatory efficiency. On the contrary, evidence remains inconclusive about reduced peripheral oxygen extraction, impaired heart rate adjustment, and lower anaerobic threshold, compared to non-diabetic subjects. Based on the multiparametric evaluation provided by imaging-CPET, a dissection and a hierarchy of the underlying mechanisms can be obtained. Here we propose four possible integrated pathophysiological mechanisms, namely myocardiogenic, myogenic, vasculogenic and neurogenic. While each hypothesis alone can potentially explain the majority of the CPET alterations observed, seemingly different combinations exist in any given subject. Finally, a discussion on the effects -and on the physiological mechanisms-of physical activity and exercise training on oxygen uptake in T2DM subjects is also offered. The understanding of the early alterations in the cardiopulmonary response that are specific of T2DM would allow the early identification of those at a higher risk of developing HF and possibly help to understand the pathophysiological link between T2DM and HF
Line failure probability bounds for power grids
We develop upper bounds for line failure probabilities in power grids, under
the DC approximation and assuming Gaussian noise for the power injections. Our
upper bounds are explicit, and lead to characterization of safe operational
capacity regions that are convex and polyhedral, making our tools compatible
with existing planning methods. Our probabilistic bounds are derived through
the use of powerful concentration inequalities
A holistic approach to forecasting wholesale energy market prices
Electricity market price predictions enable energy market participants to shape their consumption or supply while meeting their economic and environmental objectives. By utilizing the basic properties of the supply-demand matching process performed by grid operators, known as Optimal Power Flow (OPF), we develop a methodology to recover energy market's structure and predict th
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