Fine Structure Constant Variation from a Late Phase Transition

Recent experimental data indicates that the fine structure constant alpha may be varying on cosmological time scales. We consider the possibility that such a variation could be induced by a second order phase transition which occurs at late times (z ~ 1 - 3) and involves a change in the vacuum expectation value (vev) of a scalar with milli-eV mass. Such light scalars are natural in supersymmetric theories with low SUSY breaking scale. If the vev of this scalar contributes to masses of electrically charged fields, the low-energy value of alpha changes during the phase transition. The observational predictions of this scenario include isotope-dependent deviations from Newtonian gravity at sub-millimeter distances, and (if the phase transition is a sharp event on cosmological time scales) the presence of a well-defined step-like feature in the alpha(z) plot. The relation between the fractional changes in alpha and the QCD confinement scale is highly model dependent, and even in grand unified theories the change in alpha does not need to be accompanied by a large shift in nucleon masses.Comment: 9 pages. V2: discussion on the energy density stored in the scalar oscillations after the phase transition expanded. Typos corrected and Refs. added. Version to appear in PL

Realistic Anomaly Mediation with Bulk Gauge Fields

We present a simple general framework for realistic models of supersymmetry breaking driven by anomaly mediation. We consider a 5-dimensional "brane universe" where the visible and hidden sectors are localized on different branes, and the standard model gauge bosons propagate in the bulk. In this framework there can be charged scalar messengers that have contact interactions with the hidden sector, either localized in the hidden sector or in the bulk. These scalars obtain soft masses that feed into visible sector scalar masses at two loop order via bulk gauge interactions. This contribution is automatically flavor-blind, and can be naturally positive. If the messengers are in the bulk this contribution is automatically the same order of magnitude as the anomaly mediated contribution, independent of the brane spacing. If the messengers are localized to a brane the two effects are of the same order for relatively small brane spacings. The gaugino masses and A terms are determined completely by anomaly mediation. In order for anomaly mediation to dominate over radion mediation the radion must be is stabilized in a manner that preserves supersymmetry, with supergravity effects included. We show that this occurs in simple models. We also show that the mu problem can be solved by the vacuum expectation value of a singlet in this framework.Comment: 16 pages, LaTeX2e, no figure

Dynamic Consumption and Portfolio Choice with Stochastic Volatility in Incomplete Markets

This paper analyzes optimal portfolio choice and consumption with stochastic volatility in incomplete markets. Using the Duffie-Epstein (1992) formulation of recursive utility in continuous time, it shows that the optimal portfolio demand for stocks under stochastic volatility varies strongly with the investor's coefficient of relative risk aversion, but only slightly with her elasticity of intertemporal substitution; by contrast, optimal consumption relative to wealth depends on both preference parameters. This paper also shows that stochastic variation in volatility produces an optimal intertemporal hedging demand for stocks which is negative when changes in volatility are instantaneously negatively correlated with excess stock returns and investors have coefficients of relative risk aversion larger than one. The absolute size of this demand increases with the size of this correlation, and also with the persistence of shocks to volatility. An application to the US stock market shows that empirically this correlation is negative and large, which implies a negative hedging demand for stocks. This application also shows that only low frequency shocks to volatility exhibit enough persistence to generate sizable hedging demands by long-term, risk averse investors. A comparative statics exercise shows that the size of hedging demands is considerably more sensitive to changes in persistence than to changes in correlation.

Dynamic Consumption and Portfolio Choice with Stochastic Volatility in Incomplete Markets

This paper analyzes optimal portfolio choice and consumption with stochastic volatility in incomplete markets. Using the Duffie-Epstein (1992) formulation of recursive utility in continuous time, it shows that the optimal portfolio demand for stocks under stochastic volatility varies strongly with the investor's coefficient of relative risk aversion, but only slightly with her elasticity of intertemporal substitution;by contrast, optimal consumption relative to wealth depends on both preference parameters. This paper also shows that stochastic variation in volatility produces an optimal intertemporal heding demand for stocks which is negative when changes in volatility are instantaneously negatively correlated with excess stock returns and investors have coefficients of relative risk aversion larger than one. The absolute size of this demand increase with the size of this correlation, and also with the persistence of shocks to volatility. An application to the US stock market shows that empirically this correlation is negative and large, which implies a negative hedging demand for stocks. This application also shows that only low frequency shocks to volatility exhibit enough persistence to generate sizable hedging demands by long-term, risk averse investors. A comparative statics exercise shows that the size of hedging deamnds is considerably more sensitive to changes in correlation.Intertemporal portfolio choice, continuous-time, stochastic volatility, long-term investors, recursive utility, characteristic function, spectral GMM.

The Structural Basis for the Phosphorylation-Induced Activation of Smad Proteins: a Dissertation

The Smad proteins transduce the signal of transforming growth factor-β (TGF-β) and related factors from the cell surface to the nucleus. Following C-terminal phosphorylation by a corresponding receptor kinase, the R-Smad proteins form heteromeric complexes with Smad4. These complexes translocate into the nucleus, bind specific transcriptional activators and DNA, ultimately modulating gene expression. Though studied through a variety of means, the stoichiometry of the R-Smad/Smad4 complex is unclear. We investigated the stoichiometry of the phosphorylation-induced R-Smad/Smad4 complex by using acidic amino acid substitutions to simulate phosphorylation. Size exclusion chromatography, analytical ultracentrifugation, and isothermal titration calorimetry analysis revealed that the R-Smad/Smad4 complex is a heterotrimer consisting of two R-Smad subunits and one Smad4 subunit. In addition, a specific mechanism for phosphorylation-induced R-Smad/Smad4 complex formation was studied. Although it had been previously established that part of the mechanism through which phosphorylation induces Smad oligomerization is through relieving MH1-domain mediated autoinhibition of the MH2 (oligomerization) domain, it is also evident that phosphorylation serves to energetically drive Smad complex formation. Through mutational and size exclusion chromatography analysis, we established that phosphorylation induces oligomerization of the Smads by creating an electrostatic interaction between the phosphorylated C-terminal tail of one R-Smad subunit in a Smad trimer with a basic surface on an adjacent R-Smad or Smad4 subunit. The basic surface is defined largely by the L3 loop, a region that had previously been implicated in R-Smad interaction with the receptor kinase. Furthermore, the Smad MH2 domain shares a similar protein fold with the phosphoserine and phosphothreonine-binding FHA domains from proteins like Rad53 and Chk2. Taken together, these results suggest that the Smad MH2 domain may be a distinct phospho serine-binding domain, which utilizes a common basic surface to bind the receptor kinase and other Smads, and takes advantage of phosphorylation-induced allosteric changes dissociate from the receptor kinase and oligomerize with other Smads. Finally, the structural basis for the preferential formation of the R-Smad/Smad4 heterotrimeric complex over the R-Smad homotrimeric complex was explored through X-ray crystallography and isothermal titration calorimetry. Crystal structures of the Smad2/Smad4 and Smad3/Smad4 complexes revealed that specific residue differences in Smad4 compared to R-Smads resulted in highly favorable electrostatic interactions that explain the preference for the interaction with Smad4

Connecting Linguistic Expressions and Pain Relief Through Transformer Model Construction and Analysis

Chronic pain is a widespread problem that significantly impacts quality of life. Overprescription and abuse of pain medication continues to be a major public health issue and can further burden patients due to a fragmented health care system. Previous research has suggested a possible psychological basis to pain and the potential for safer, non-pharmacological alternatives for pain relief. This project leverages language models to study chronic pain development and relief through psychological treatments, which will be assessed through responses to post-treatment interviews. A transformer-based natural language processing model is employed to identify connections between language expressions and pain on a dataset of back pain questionnaires. The features of the text are further analyzed through SHAP analysis to explain the model’s predictions. From the results, we discovered no significant correlation between the predicted and observed values of the general regression and classification models. We also found a slightly stronger correlation for the regression model for the placebo treatment, and no transfer in performance from generated data-trained regression and classification models. Further study of this topic could lead to more reliable prediction of pain relief by linguistic features

Associated production of the charged Higgs boson and single top quark at the LHC

The left-right twin Higgs(LRTH) model predicts the existence of the charged Higgs $\phi^{\pm}$. In this paper, we study the production of the charged Higgs boson $\phi^{-}$ with single top quark via the process $bg\to t\phi^{-}$ at the $CERN$ Large Hadron Collider(LHC). The numerical results show that the production cross section can reach the level of $10 pb$ in the reasonable parameter space of the LRTH model. We expect that, as long as it is not too heavy, the possible signatures of the heavy charged Higgs boson $\phi^{-}$ might be detected via the decay mode $\phi^{-}\to \bar{t}b$ at the LHC experiments.Comment: This paper has been withdrawn by the author(s) due to some mistakes in this pape

Strategic Asset Allocation in a Continuous-Time VAR Model

This note derives an approximate solution to a continuous-time intertemporal portfolio and consumption choice problem. The problem is the continuous-time equivalent of the discrete-time problem studied by Campbell and Viceira (1999), in which the expected excess return on a risky asset follows an AR(1)process, while the riskless interest rate is constant. The note also shows how to obtain continuous-time parameters that are consistent with discrete-time econometric estimates. The continuous-time solution is numerically close to that of Campbell and Viceira and has the property that conservative long-term investors have a large positive intertemporal hedging demand for stocks.