Masslessness in nn-dimensions

We determine the representations of the ``conformal'' group ${\bar{SO}}_0(2, n)$, the restriction of which on the ``Poincar\'e'' subgroup ${\bar{SO}}_0(1, n-1).T_n$ are unitary irreducible. We study their restrictions to the ``De Sitter'' subgroups ${\bar{SO}}_0(1, n)$ and ${\bar{SO}}_0(2, n-1)$ (they remain irreducible or decompose into a sum of two) and the contraction of the latter to ``Poincar\'e''. Then we discuss the notion of masslessness in $n$ dimensions and compare the situation for general $n$ with the well-known case of 4-dimensional space-time, showing the specificity of the latter.Comment: 34 pages, LaTeX2e, 1 figure. To be published in Reviews in Math. Phy

Estimating the Effect of Hungarian Monetary Policy within a Structural VAR Framework

A standard approach in measuring the effect of monetary policy on output and prices is to estimate a VAR model, characterise somehow the monetary policy shock and then plot impulse responses. In this paper I attempt to do this exercise with Hungarian data. I compare two identification approaches. One of them involves the ‘sign restrictions on impulse responses’ strategy applied recently by several authors. I also propose another approach, namely, imposing restrictions on implied shock history. My argument is that in certain cases, especially in the case of the Hungarian economy, the latter identification scheme may be more credible. In order to obtain robust results I use two datasets. To tackle possible structural breaks I make alternative estimates on a shorter sample as well. The main conclusions are the followings: (1) although the two identification approaches produced very similar results, imposing restrictions on history may help to dampen counterintuitive reaction of prices; (2) after 1995 a typical unanticipated monetary policy contraction (a roughly 25 basis points rate hike) resulted in an immediate 1 per cent appreciation of the nominal exchange rate (3) followed by a 0.3% lower output and 0.1-0.15% lower consumer prices; (4) the impact on prices is slower than on output; it reaches its bottom 4-6 years after the shock, resembling the intuitive choreography of sticky-price models; (5) using additional observations prior to 1995 makes identification more difficult indicating the presence of a marked structural break.structural VAR, monetary transmission mechanism, identification, sign restriction, monetary policy shocks

The real effects of financial stress in the Euro zone

Using two identification strategies based on a Bayesian Structural VAR and a Sign-Restriction VAR, we examine the real effects of financial stress in the Eurozone. In particular, we assess the macroeconomic impact of: (i) a monetary policy shock; and (ii ) a financial stress shock. We find that a monetary policy contraction strongly deteriorates financial stress conditions. In addition, unexpected variation in the Financial Stress Index (FSI) plays an important role in explaining output fluctuations, and also demands an aggressive response by the monetary authority to stabilise output indicating a preference shift from targeting inflation as it is currently happening in major economies. Therefore, our paper reveals the importance of adopting a vigilant posture towards financial stress conditions, as well as the urgency of macro-prudential risk management.monetary policy, financial stress, Bayesian Structural VAR, Sign-Restrictions, Euro-zone.

Tensor network representations from the geometry of entangled states

Tensor network states provide successful descriptions of strongly correlated quantum systems with applications ranging from condensed matter physics to cosmology. Any family of tensor network states possesses an underlying entanglement structure given by a graph of maximally entangled states along the edges that identify the indices of the tensors to be contracted. Recently, more general tensor networks have been considered, where the maximally entangled states on edges are replaced by multipartite entangled states on plaquettes. Both the structure of the underlying graph and the dimensionality of the entangled states influence the computational cost of contracting these networks. Using the geometrical properties of entangled states, we provide a method to construct tensor network representations with smaller effective bond dimension. We illustrate our method with the resonating valence bond state on the kagome lattice.Comment: 35 pages, 9 figure

On equivalency of various geometric structures

In the literature we see that after introducing a geometric structure by imposing some restrictions on Riemann-Christoffel curvature tensor, the same type structure given by imposing same restriction on other curvature tensors being studied. The main object of the present paper is to study the equivalency of various geometric structures obtained by same restriction imposing on different curvature tensors. In this purpose we present a tensor by combining Riemann-Christoffel curvature tensor, Ricci tensor, the metric tensor and scalar curvature which describe various curvature tensors as its particular cases.Comment: The paper contains 27 pages, 3 tables and 2 tree diagra

Monetary explanations of the Great Depression: a selective survey of empirical evidence

Seventy years after the Great Depression, economists still debate the causes of this economic catastrophe. Two leading explanations are distinguished by whether or not the Federal Reserve’s monetary policies are perceived as being chiefly responsible for propagating and magnifying the initial contraction into a depression. ; This article surveys recent modeling efforts and empirical work that examine aggregate explanations for the Great Depression from both the extensive literature using vector autoregression techniques and the more recent literature using dynamic stochastic general equilibrium modeling. Neither of these approaches has yielded a consensus about the causes of the depression. ; Data alone are insufficient to distinguish the precise role of monetary policy during that period. The modeling strategies impose restrictions that help isolate the meaningful economic interactions in the data. In each literature, the ways in which the respective models identify monetary policy can differ substantially, and these differences are why monetary policy shocks may or may not explain much of the output contraction. Also, these modeling approaches vary in their ability to capture important institutional features of the banking and financial system. ; The authors believe that the search for one conclusive empirical study of the Great Depression is futile. The most promising path for future research models, they conclude, will entail a sharper focus on the financial sector, a refined specification of how monetary policy affects the real economy, and further methods to incorporate elements of labor market frictions.