34 research outputs found
Can A Pseudo-Nambu-Goldstone Higgs Lead To Symmetry Non-Restoration?
The calculation of finite temperature contributions to the scalar potential
in a quantum field theory is similar to the calculation of loop corrections at
zero temperature. In natural extensions of the Standard Model where loop
corrections to the Higgs potential cancel between Standard Model degrees of
freedom and their symmetry partners, it is interesting to contemplate whether
finite temperature corrections also cancel, raising the question of whether a
broken phase of electroweak symmetry may persist at high temperature. It is
well known that this does not happen in supersymmetric theories because the
thermal contributions of bosons and fermions do not cancel each other. However,
for theories with same spin partners, the answer is less obvious. Using the
Twin Higgs model as a benchmark, we show that although thermal corrections do
cancel at the level of quadratic divergences, subleading corrections still
drive the system to a restored phase. We further argue that our conclusions
generalize to other well-known extensions of the Standard Model where the Higgs
is rendered natural by being the pseudo-Nambu-Goldstone mode of an approximate
global symmetry.Comment: 21 pages, 5 figures. v2: fixed problem related to references with
9-digit arXiv identifiers. v3: references added v4: Some clarifications and
more references added; matches published versio
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Aspects of new physics beyond the standard model : electroweak naturalness, dark matter and holographic quantum gravity
This dissertation is based on studies of three aspects of physics beyond the Standard Model. First, we summarize a study of high temperature symmetry restoration in extensions of the Standard Model where the naturalness problem is resolved due to the Higgs being a pseudo-Nambu-Goldstone boson. Second, we analyze a framework for building quantum field theoretic models where dark matter has its cosmic origins in an asymmetry, while the overall dark charge is conserved and the dark matter relic is actually symmetric at late times. Finally, we study the relation between holographic `bulk' geometry, and the structure of entanglement in the quantum field theory living on the boundary as characterized by the Multiscale Entanglement Renormalization Ansatz (MERA).Physic
Fast exploration and learning of latent graphs with aliased observations
We consider the problem of recovering a latent graph where the observations
at each node are \emph{aliased}, and transitions are stochastic. Observations
are gathered by an agent traversing the graph. Aliasing means that multiple
nodes emit the same observation, so the agent can not know in which node it is
located. The agent needs to uncover the hidden topology as accurately as
possible and in as few steps as possible. This is equivalent to efficient
recovery of the transition probabilities of a partially observable Markov
decision process (POMDP) in which the observation probabilities are known. An
algorithm for efficiently exploring (and ultimately recovering) the latent
graph is provided. Our approach is exponentially faster than naive exploration
in a variety of challenging topologies with aliased observations while
remaining competitive with existing baselines in the unaliased regime
Schema-learning and rebinding as mechanisms of in-context learning and emergence
In-context learning (ICL) is one of the most powerful and most unexpected
capabilities to emerge in recent transformer-based large language models
(LLMs). Yet the mechanisms that underlie it are poorly understood. In this
paper, we demonstrate that comparable ICL capabilities can be acquired by an
alternative sequence prediction learning method using clone-structured causal
graphs (CSCGs). Moreover, a key property of CSCGs is that, unlike
transformer-based LLMs, they are {\em interpretable}, which considerably
simplifies the task of explaining how ICL works. Specifically, we show that it
uses a combination of (a) learning template (schema) circuits for pattern
completion, (b) retrieving relevant templates in a context-sensitive manner,
and (c) rebinding of novel tokens to appropriate slots in the templates. We go
on to marshall evidence for the hypothesis that similar mechanisms underlie ICL
in LLMs. For example, we find that, with CSCGs as with LLMs, different
capabilities emerge at different levels of overparameterization, suggesting
that overparameterization helps in learning more complex template (schema)
circuits. By showing how ICL can be achieved with small models and datasets, we
open up a path to novel architectures, and take a vital step towards a more
general understanding of the mechanics behind this important capability
Acquired rifampicin resistance in thrice-weekly antituberculosis therapy: impact of HIV and antiretroviral therapy
Risk factors for acquired rifampicin resistance (ARR) among tuberculosis patients on thrice-weekly antituberculosis therapy were baseline isoniazid resistance and HIV. Among HIV-infected patients, higher mycobacterial burden and lower CD4 count, but not highly active antiretroviral therapy, were significantly associated with ARR. Background: Risk factors for acquired rifampicin resistance (ARR) in human immunodeficiency virus (HIV)/tuberculosis coinfection, in the highly active antiretroviral therapy (HAART) era, needs evaluation. We studied the impact of HIV and HAART on ARR among patients taking thrice-weekly antituberculosis therapy. Methods: This cross-protocol analysis included patients with newly diagnosed, rifampicin-susceptible pulmonary tuberculosis, with and without HIV, enrolled in clinical trials (who took >80% of medication) at the National Institute for Research in Tuberculosis between 1999 and 2013. All patients received rifampicin and isoniazid for 6 months reinforced with pyrazinamide and ethambutol in the first 2 months, given thrice-weekly throughout the study along with HAART in one of the groups. Outcomes were categorized and multivariate logistic regression analysis performed to identify risk factors for ARR. Results: The per-protocol results included patients with tuberculosis: 246 HIV-uninfected patients (HIV–TB+), 212 HIV patients not on HAART (non-HAART), and 116 HIV-infected patients on HAART. Median CD4 counts of the latter 2 groups were 150 and 93 cells/μL, respectively, and the median viral loads were 147 000 and 266 000 copies/mL, respectively. Compared with HIV–TB+, the relative risks (RRs) for an unfavorable response in the coinfected, non-HAART and HAART groups were 2.1 (95% confidence interval [CI], 1.7–14.8; P<.0001) and 2.1 (95% CI, .9–5.2; P=.3), whereas for ARR, the RRs were 21.1 (95% CI, 2.6–184; P<.001) and 8.2 (95% CI, .6–104; P=.07), respectively. Conclusions: HIV-infected patients with tuberculosis treated with a thrice-weekly antituberculosis regimen are at a higher risk of ARR, compared with HIV-uninfected patients, in the presence of baseline isoniazid resistance. HAART reduces but does not eliminate the risk of ARR