Strong coupling from the Hubbard model

It was recently observed that the one dimensional half-filled Hubbard model reproduces the known part of the perturbative spectrum of planar N=4 super Yang-Mills in the SU(2) sector. Assuming that this identification is valid beyond perturbation theory, we investigate the behavior of this spectrum as the 't Hooft parameter \lambda becomes large. We show that the full dimension \Delta of the Konishi superpartner is the solution of a sixth order polynomial while \Delta for a bare dimension 5 operator is the solution of a cubic. In both cases the equations can be solved easily as a series expansion for both small and large \lambda and the equations can be inverted to express \lambda as an explicit function of \Delta. We then consider more general operators and show how \Delta depends on \lambda in the strong coupling limit. We are also able to distinguish those states in the Hubbard model which correspond to the gauge invariant operators for all values of \lambda. Finally, we compare our results with known results for strings on AdS_5\times S^5, where we find agreement for a range of R-charges.Comment: 14 pages; v2: 17 pages, 2 figures, appendix and references added; typos fixed, minor changes; v3 fixed figures; v4 more references added, minor correctio

Automated data pre-processing via meta-learning

The final publication is available at link.springer.comA data mining algorithm may perform differently on datasets with different characteristics, e.g., it might perform better on a dataset with continuous attributes rather than with categorical attributes, or the other way around. As a matter of fact, a dataset usually needs to be pre-processed. Taking into account all the possible pre-processing operators, there exists a staggeringly large number of alternatives and nonexperienced users become overwhelmed. We show that this problem can be addressed by an automated approach, leveraging ideas from metalearning. Specifically, we consider a wide range of data pre-processing techniques and a set of data mining algorithms. For each data mining algorithm and selected dataset, we are able to predict the transformations that improve the result of the algorithm on the respective dataset. Our approach will help non-expert users to more effectively identify the transformations appropriate to their applications, and hence to achieve improved results.Peer ReviewedPostprint (published version

Dephasing of a Qubit due to Quantum and Classical Noise

The qubit (or a system of two quantum dots) has become a standard paradigm for studying quantum information processes. Our focus is Decoherence due to interaction of the qubit with its environment, leading to noise. We consider quantum noise generated by a dissipative quantum bath. A detailed comparative study with the results for a classical noise source such as generated by a telegraph process, enables us to set limits on the applicability of this process vis a vis its quantum counterpart, as well as lend handle on the parameters that can be tuned for analyzing decoherence. Both Ohmic and non-Ohmic dissipations are treated and appropriate limits are analyzed for facilitating comparison with the telegraph process.Comment: 12 pages, 8 figure

Open Spin Chains in Super Yang-Mills at Higher Loops: Some Potential Problems with Integrability

The super Yang-Mills duals of open strings attached to maximal giant gravitons are studied in perturbation theory. It is shown that non-BPS baryonic excitations of the gauge theory can be studied within the paradigm of open quantum spin chains even beyond the leading order in perturbation theory. The open spin chain describing the two loop mixing of non-BPS giant gravitons charged under an su(2) of the so(6) R symmetry group is explicitly constructed. It is also shown that although the corresponding open spin chain is integrable at the one loop order, there is a potential breakdown of integrability at two and higher loops. The study of integrability is performed using coordinate Bethe ansatz techniques.Comment: 28 pages. References added in revised versio

On the Scattering Phase for AdS_5 x S^5 Strings

We propose a phase factor of the worldsheet S-matrix for strings on AdS_5 x S^5 apparently solving Janik's crossing relation.Comment: 9 pages, v2: revised conclusions about agreement with perturbative string theory; minor changes, v3: resolution to above problems indicated, to appear in Mod. Phys. Lett.

A Classification of random Dirac fermions

We present a detailed classification of random Dirac hamiltonians in two spatial dimensions based on the implementation of discrete symmetries. Our classification is slightly finer than that of random matrices, and contains thirteen classes. We also extend this classification to non-hermitian hamiltonians with and without Dirac structure.Comment: 15 pages, version2: typos in the table of classes are correcte

The effect of COVID-19 on the home behaviours of people affected by dementia

The COVID-19 pandemic has dramatically altered the behaviour of most of the world's population, particularly affecting the elderly, including people living with dementia (PLwD). Here we use remote home monitoring technology deployed into 31 homes of PLwD living in the UK to investigate the effects of COVID-19 on behaviour within the home, including social isolation. The home activity was monitored continuously using unobtrusive sensors for 498 days from 1 December 2019 to 12 April 2021. This period included six distinct pandemic phases with differing public health measures, including three periods of home 'lockdown'. Linear mixed-effects modelling is used to examine changes in the home activity of PLwD who lived alone or with others. An algorithm is developed to quantify time spent outside the home. Increased home activity is observed from very early in the pandemic, with a significant decrease in the time spent outside produced by the first lockdown. The study demonstrates the effects of COVID-19 lockdown on home behaviours in PLwD and shows how unobtrusive home monitoring can be used to track behaviours relevant to social isolation

Semiclassical short strings in AdS_5 x S^5

We present results for the one-loop correction to the energy of a class of string solutions in AdS_5 x S^5 in the short string limit. The computation is based on the observation that, as for rigid spinning string elliptic solutions, the fluctuation operators can be put into the single-gap Lame' form. Our computation reveals a remarkable universality of the form of the energy of short semiclassical strings. This may help to understand better the structure of the strong coupling expansion of the anomalous dimensions of dual gauge theory operators.Comment: 12 pages, one pdf figure. Invited Talk at 'Nonlinear Physics. Theory and Experiment VI', Gallipoli (Italy) - June 23 - July 3, 201

Attitudes towards Oral Health in Patients with Rheumatoid Arthritis: A Qualitative Study Nested within a Randomized Controlled Trial

Introduction: Patients with rheumatoid arthritis (RA) present a higher incidence and severity of periodontitis than the general population. Our study, Outcomes of Periodontal Treatment in Patients with Rheumatoid Arthritis (OPERA), was a randomized waiting-list controlled trial using mixed methods. Patients randomized to the intervention arm received intensive periodontal treatment, and those in the control arm received the same treatment with a 6-mo delay. Aim: The nested qualitative component aimed to explore patients’ experiences and priorities concerning oral health and barriers and facilitators for trial participation. Methods: Using purposive sampling until thematic saturation was reached, we conducted 21 one-to-one semistructured interviews with randomized patients in either of the 2 treatment arms as well as with patients who did not consent for trial participation. Results: The patients described their experiences about RA, oral health, and study participation. Previous experiences with dental care professionals shaped patients’ current perceptions about oral health and the place of oral health on their list of priorities compared with other conditions. Patients also highlighted some of the barriers and facilitators for study participation and for compliance with oral health maintenance. The patients, in the control arm, presented their views regarding the acceptable length of waiting time for the intervention. Conclusion: The associations between periodontal and systemic health are increasingly recognized by the literature. Our study provided an insight into RA patients’ experiences and perceptions about oral health. It also highlighted some of the barriers and facilitators for participating in a periodontal interventional study for this group. We hope that our findings will support the design of larger interventional periodontal studies in patients with RA. The complex challenges faced by the burden of RA and the associated multimorbidities in this patient group might highlight opportunities to improve access to oral health services in this patient population. Knowledge Transfer Statement: This article provided insights into the experiences and perceptions of rheumatoid arthritis patients about their oral health to improve patient participation in a definitive clinical trial