Kosterlitz-Thouless Universality in a Fermionic System

A new extension of the attractive Hubbard model is constructed to study the critical behavior near a finite temperature superconducting phase transition in two dimensions using the recently developed meron-cluster algorithm. Unlike previous calculations in the attractive Hubbard model which were limited to small lattices, the new algorithm is used to study the critical behavior on lattices as large as $128\times 128$. These precise results for the first time show that a fermionic system can undergo a finite temperature phase transition whose critical behavior is well described by the predictions of Kosterlitz and Thouless almost three decades ago. In particular it is confirmed that the spatial winding number susceptibility obeys the well known predictions of finite size scaling for $T<T_c$ and up to logarithmic corrections the pair susceptibility scales as $L^{2-\eta}$ at large volumes with $0\leq\eta\leq 0.25$ for $0\leq T\leq T_c$.Comment: Revtex format; 4 pages, 2 figure

Fermion loop simulation of the lattice Gross-Neveu model

We present a numerical simulation of the Gross-Neveu model on the lattice using a new representation in terms of fermion loops. In the loop representation all signs due to Pauli statistics are eliminated completely and the partition function is a sum over closed loops with only positive weights. We demonstrate that the new formulation allows to simulate volumes which are two orders of magnitude larger than those accessible with standard methods

Mortality of olive ridley turtles during nesting season along Chennai coast

Sporadic nesting activities of olive ridley turtle (Lepidochelys olivacea) are often reported along the Chennai coast in northern Tamil Nadu. These turtles approach the beaches for nesting in the Tamil month of Panguni and have thus derived the local name “Panguni aamai”. As in every year, with the onset of annual nesting season in early 2017, mortality of turtles along the Chennai coast was recorded. From 02.01.2017 to 07.01.2017, a total of seven adult turtle carcasses were observed in 20km stretch of beach between Marina beach and Kanathur Reddykuppam

Cluster Algorithms for Quantum Impurity Models and Mesoscopic Kondo Physics

Nanoscale physics and dynamical mean field theory have both generated increased interest in complex quantum impurity problems and so have focused attention on the need for flexible quantum impurity solvers. Here we demonstrate that the mapping of single quantum impurity problems onto spin-chains can be exploited to yield a powerful and extremely flexible impurity solver. We implement this cluster algorithm explicitly for the Anderson and Kondo Hamiltonians, and illustrate its use in the ``mesoscopic Kondo problem''. To study universal Kondo physics, a large ratio between the effective bandwidth $D_\mathrm{eff}$ and the temperature $T$ is required; our cluster algorithm treats the mesoscopic fluctuations exactly while being able to approach the large $D_\mathrm{eff}/T$ limit with ease. We emphasize that the flexibility of our method allows it to tackle a wide variety of quantum impurity problems; thus, it may also be relevant to the dynamical mean field theory of lattice problems.Comment: 4 pages, 3 figure

On the Sign Problem in the Hirsch-Fye Algorithm for Impurity Problems

We show that there is no fermion sign problem in the Hirsch and Fye algorithm for the single-impurity Anderson model. Beyond the particle-hole symmetric case for which a simple proof exists, this has been known only empirically. Here we prove the nonexistence of a sign problem for the general case by showing that each spin trace for a given Ising configuration is separately positive. We further use this insight to analyze under what conditions orbitally degenerate Anderson models or the two-impurity Anderson model develop a sign.Comment: 2 pages, no figure; published versio

Cytological studies on diploid and autotetraploid ginger (Zingiber officinale Rosc.)

Cytology of diploid and induced autotetl'aploid of ginger (Zingiber officinale&nbsp;Rosc.) was studied. The diploid (2n=22) showed one or two associations offour chromosomes at first metaphase. The tetraploid formed a high frequency of quadrivalents at first metaphase. Both showed bridge-fragment configurations at first anaphase. Pol1en fertility was 13% in the diploid and 85% in the tetraploid. &nbsp

Cytological studies on diploid and autotetraploid ginger (Zingiber officinale Rosc.)

Cytology of diploid and induced autotetl'aploid of ginger (Zingiber officinale&nbsp;Rosc.) was studied. The diploid (2n=22) showed one or two associations offour chromosomes at first metaphase. The tetraploid formed a high frequency of quadrivalents at first metaphase. Both showed bridge-fragment configurations at first anaphase. Pol1en fertility was 13% in the diploid and 85% in the tetraploid. &nbsp

Non-perturbative Quantum Dynamics of the Order Parameter in the Pairing Model

We consider quantum dynamics of the order parameter in the discrete pairing model (Richardson model) in thermodynamic equilibrium. The integrable Richardson Hamiltonian is represented as a direct sum of Hamiltonians acting in different Hilbert spaces of single-particle and paired/empty states. This allows us to factorize the full thermodynamic partition function into a combination of simple terms associated with real spins on singly-occupied states and the partition function of the quantum XY-model for Anderson pseudospins associated with the paired/empty states. Using coherent-state path-integral, we calculate the effects of superconducting phase fluctuations exactly. The contribution of superconducting amplitude fluctuations to the partition function in the broken-symmetry phase is shown to follow from the Bogoliubov-de Gennes equations in imaginary time. These equations in turn allow several interesting mappings, e.g., they are shown to be in a one-to-one correspondence with the one-dimensional Schr\"odinger equation in supersymmetric Quantum Mechanics. However, the most practically useful approach to calculate functional determinants is found to be via an analytical continuation of the quantum order parameter to real time, \Delta(\tau -> it), such that the problem maps onto that of a driven two-level system. The contribution of a particular dynamic order parameter to the partition function is shown to correspond to the sum of the Berry phase and dynamic phase accumulated by the pseudospin. We also examine a family of exact solutions for two-level-system dynamics on a class of elliptic functions and suggest a compact expression to estimate the functional determinants on such trajectories. The possibility of having quantum soliton solutions co-existing with classical BCS mean-field is discussed.Comment: 34 pages (v2: Typos corrected, references added