Structure of the broken phase of the sine-Gordon model using functional renormalization

We study in this paper the sine-Gordon model using functional Renormalization Group (fRG) at Local Potential Approximation (LPA) using different RG schemes. In $d=2$, using Wegner-Houghton RG we demonstrate that the location of the phase boundary is entirely driven by the relative position to the Coleman fixed point even for strongly coupled bare theories. We show the existence of a set of IR fixed points in the broken phase that are reached independently of the bare coupling. The bad convergence of the Fourier series in the broken phase is discussed and we demonstrate that these fixed-points can be found only using a global resolution of the effective potential. We then introduce the methodology for the use of Average action method where the regulator breaks periodicity and show that it provides the same conclusions for various regulators. The behavior of the model is then discussed in $d\ne 2$ and the absence of the previous fixed points is interpreted.Comment: 43 pages, 32 figures, accepted versio

Tiny x86 - Architecture Simulator for Educational Purposes

Tato práce prezentuje tiny x86 architekturu a virtuální stroj, určené jako pomocný nástroj studentům k porozumění technikám kompilování a jejich dopad na výkon programu. V porovnání s již existujícími instrukčními sadami je tiny x86 jednodušší na použití, protože oproti binárnímu kódování nabízí aplikační rozhraní v jazyce C++ a nelimituje se na jeden návrh (jsou podporovány prvky CISC i RISC architektury). Prezentovaný virtuální stroj nabízí rozsáhle možnosti konfigurace, dovolující z(ne)výraznit různé návrhové prvky (počet registrů, odezvu paměti, trvání instrukcí atd.). Virtuální stroj je již nasazen v předmětu NI-GEN (generování kódu) na FIT ČVUT, kde jeho jednoduchost dovoluje studentům během semestru psát kompletní kompilátor.This thesis presents tiny x86 architecture and virtual machine designed to help students understand various compiler techniques and their effect on the program performance. Compared to existing instruction set architectures, tiny x86 is simpler, easier to use as it comes with a C++ API as opposed to binary encodings and does not limit itself to single design principles (both CISC and RISC features are supported). The VM also offers extensive configuration options, allowing it to (de-)emphasize various architecture features (register pressure, memory latency, instruction timings, etc.). The VM is already used in the NI-GEN (Code Generation) course at FIT CTU, where its simplicity allows the students to write full compiler pipeline during the term

Valuing PSS outputs and quality changes

The Gershon review of efficiency recommended that target improvements in efficiency should be met both through financial savings and through improvements in quality of outputs. This paper reports on a pilot project designed to feed into an approach for local authorities to quantify in monetary terms quality gains in the provision of personal social services (PSS), with a specific application to the provision of home care for older people. There are a number of practical and theoretical problems with attributing monetary values to aspects of quality. The approach described here builds on ongoing work into the measurement of PSS outputs for the purposes of National Accounts and measuring changes in productivity and efficiency more widely. This approach distinguishes what services could provide (capacity for benefit) from the quality of what is provided in practice. By attaching a financial valuation to capacity for benefit we are able to attribute a monetary valuation to changes in the quality of provision measured (in the case of home care) through service user experiences of their care. Capacity for benefit (CfB) is defined in terms of eight domains of outcome that services address and four levels of need (no needs, all needs met, low needs, high needs) within these domains. In addition we identify whether people are living in their own homes, as a key attribute of care provision. The characteristics of the service (in terms of domains of outcome and whether living at home) and service users (in terms of level of need that need to be met) determine the CfB of a given service

Doping a Mott Insulator: Physics of High Temperature Superconductivity

This article reviews the effort to understand the physics of high temperature superconductors from the point of view of doping a Mott insulator. The basic electronic structure of the cuprates is reviewed, emphasizing the physics of strong correlation and establishing the model of a doped Mott insulator as a starting point. A variety of experiments are discussed, focusing on the region of the phase diagram close to the Mott insulator (the underdoped region) where the behavior is most anomalous. We introduce Anderson's idea of the resonating valence bond (RVB) and argue that it gives a qualitative account of the data. The importance of phase fluctuation is discussed, leading to a theory of the transition temperature which is driven by phase fluctuation and thermal excitation of quasiparticles. We then describe the numerical method of projected wavefunction which turns out to be a very useful technique to implement the strong correlation constraint, and leads to a number of predictions which are in agreement with experiments. The remainder of the paper deals with an analytic treatment of the t-J model, with the goal of putting the RVB idea on a more formal footing. The slave-boson is introduced to enforce the constraint of no double occupation. The implementation of the local constraint leads naturally to gauge theories. We give a rather thorough discussion of the role of gauge theory in describing the spin liquid phase of the undoped Mott insulator. We next describe the extension of the SU(2) formulation to nonzero doping. We show that inclusion of gauge fluctuation provides a reasonable description of the pseudogap phase.Comment: 69 pages, 36 fgiures. Submitted to Rev. Mod. Phy

Disassembling the Trust Machine, three cuts on the political matter of blockchain

Blockchain technology is, in part, a proposal to resolve ‘the political’ through technical means: decentralised networks to solve the problem of authority; cryptography to coordinate and secure the network; and game theory and incentive design to solve network behaviour. This PhD thesis draws on theoretical work by Karen Barad (2007) and Jacques Rancière (Rancière, 2010) to ask the question of what matters politically in blockchain technology – both in the sense of matter as becoming material of a new mediation of the political, but also mattering in the sense of being of political importance to engineers, developers and communities forming around blockchain as a potential. Rather than treating blockchain as coherent thing to be either celebrated or criticised, this thesis proposes and attempts to draw out the ways in which the potentials of blockchain are negotiated as part of its political effects, looking towards these negotiations to understand how political differences are made and sought materialised. Three approaches to the political are articulated to analyse Bitcoin and Ethereum as case studies and shift their terms of debate. Firstly, addressing the question of algorithmic determinacy, an approach is proposed for critically understanding a blockchain proposition that does not immediately revert to a competition of control between ‘human’ and ‘machine’ through the notion of the insensible, drawing on work by geographer of the inhuman Yusoff (2013a). Secondly, drawing on political theorist Rancière (2010) a particular blockchain sensibility is articulated, addressing the question of the particular kind of ‘disruption’ that blockchain presents. Its specific provenance in political histories of decentralised network computation opens up political significance beyond its intersections with financial capitalism. Finally, addressing the question of blockchain as a resolution to the political, the thesis introduces the concept of dissensible as an ongoing potential for incompatible sensibilities and their negotiation