509 research outputs found

    Remarks on Limits on String Scale from Proton Decay and Low-Energy amplitudes in Braneworld Scenario

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    We discuss IR limit of four-fermion scattering amplitudes in braneworld models including intersecting-branes and SUSY SU(5) GUT version of it. With certain compactification where instanton effect is negligible, grand unification condition in D6-D6 intersecting-branes scenario subject to experimental constraint on proton decay provides possibility for upper limit on the string scale, MSM_S, through relationship between the string coupling, gsg_s, and the string scale. We discuss how IR divergence is related to number of twisted fields we have to introduce into intersection region and how it can change IR behaviour of tree-level amplitudes in various intersecting-branes models. Using number of twisted fields, we identify some intersecting-branes models whose tree-level amplitudes are purely stringy in nature and automatically proportional to gs/MS2g_s/M^2_{S} at low energy. They are consequently suppressed by the string scale. For comparison, we also derive limit on the lower bound of the string scale from experimental constraint on proton decay induced from purely stringy contribution in the coincident-branes model, the limit is about 10510^5 TeV.Comment: 14 page

    On Heavy-Quark Free Energies, Entropies, Polyakov Loop, and AdS/QCD

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    In this paper we explore some of the features of a heavy quark-antiquark pair at finite temperature using a five-dimensional framework nowadays known as AdS/QCD. We shall show that the resulting behavior is consistent with our qualitative expectations of thermal gauge theory. Some of the results are in good agreement with the lattice data that provides additional evidence for the validity of the proposed model.Comment: 15 pages, 10 figures; v2: comments added, misprints correcte

    Fibre Inflation: Observable Gravity Waves from IIB String Compactifications

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    We introduce a simple string model of inflation, in which the inflaton field can take trans-Planckian values while driving a period of slow-roll inflation. This leads naturally to a realisation of large field inflation, inasmuch as the inflationary epoch is well described by the single-field scalar potential V=V0(34eφ^/3)V = V_0 (3-4 e^{-\hat\varphi/\sqrt{3}}). Remarkably, for a broad class of vacua all adjustable parameters enter only through the overall coefficient V0V_0, and in particular do not enter into the slow-roll parameters. Consequently these are determined purely by the number of \e-foldings, NeN_e, and so are not independent: ε32η2\varepsilon \simeq \frac32 \eta^2. This implies similar relations among observables like the primordial scalar-to-tensor amplitude, rr, and the scalar spectral tilt, nsn_s: r6(ns1)2r \simeq 6(n_s - 1)^2. NeN_e is itself more model-dependent since it depends partly on the post-inflationary reheat history. In a simple reheating scenario a reheating temperature of Trh109T_{rh}\simeq 10^{9} GeV gives Ne58N_e\simeq 58, corresponding to ns0.970n_s\simeq 0.970 and r0.005r\simeq 0.005, within reach of future observations. The model is an example of a class that arises naturally in the context of type IIB string compactifications with large-volume moduli stabilisation, and takes advantage of the generic existence there of Kahler moduli whose dominant appearance in the scalar potential arises from string loop corrections to the Kahler potential. The inflaton field is a combination of Kahler moduli of a K3-fibered Calabi-Yau manifold. We believe there are likely to be a great number of models in this class -- `high-fibre models' -- in which the inflaton starts off far enough up the fibre to produce observably large primordial gravity waves.Comment: Extended calculations beyond the leading approximations, including numerical integrations of multi-field evolution; Display an example with r=0.01r = 0.01; Simplify the discussion of large fields; Corrected minor errors and typos; Added references; 41 pages LaTeX, 25 figure

    Systemic Therapy for Elderly Patients with Gastrointestinal Cancer

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    The majority of patients with gastrointestinal cancers are over the age of 65. This age group comprises the minority of the patients enrolled in clinical trials, and it is unknown whether older patients achieve similar results as younger patients in terms of survival benefit and tolerability. In addition, there are few studies specifically designed for patients over 65 years. Subset analyses of individual trials and studies using pooled patient data from multiple trials provide some understanding on outcomes in older patients with gastrointestinal cancers. This article reviews the evidence on chemotherapeutic regimens in the elderly with colorectal, pancreatic, and gastroesophageal cancers, and discusses a practical approach to provide the best outcomes for older patients

    Student politics, teaching politics, black politics: an interview with Ansel Wong

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    Ansel Wong is the quiet man of British black politics, rarely in the limelight and never seeking political office. And yet his ‘career’ here – from Black Power firebrand to managing a multimillion budget as head of the Greater London Council’s Ethnic Minority Unit in the 1980s – spells out some of the most important developments in black educational and cultural projects. In this interview, he discusses his identification with Pan-Africanism, his involvement in student politics, his role in the establishment of youth projects and supplementary schools in the late 1960s and 1970s, and his involvement in black radical politics in London in the same period, all of which took place against the background of revolutionary ferment in the Third World and the world of ideas, and were not without their own internal class and ethnic conflicts

    Comment on Partition Function of Anyon Gas

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    The general structure of the partition function of an anyon gas is discussed, especially in relation to statements made in Phys. Rev. Lett. 68 (1992) 1621 and Phys. Rev. Lett. 69( 1992) 2877.Comment: 5 pages, Tex (This paper, which was published in Phys. Rev. Lett. but was not available on the archives, is cited in the paper ``Calogero-Sutherland Particles as Quasisemions'', hep-th/9609063
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