arXiv subjects

Boris L. Altshuler

Publications and source records attributed to Boris L. Altshuler.

At least 55 records · Page 3Linked to original sources

arXiv2008

Higgs mechanism from fluxes and two mass hierarchies in the "fat" throat solution of Type IIA supegravity

Spectra of Kaluza-Klein gauge fields are calculated at the background of the magnetic fluxbrane throat-like solution of the Type IIA supergravity equations. Magnetic flux plays the role of Higgs scalar generating the electroweak scale mass of non-abelian KK gauge field. The same "flux-Higgs" mechanism gives the scale of the "second mass hierarchy", 0.001 eV, in the spectrum of KK excitations at the background of the throat deformed in a Reissner-Nordstrom way. Gauge coupling constants in 4 dimensions are calculated; they prove to be of the physically sensible values for the EW scale massive modes of the gauge fields and are extremely small for the long range gauge fields. 5D effective Action with the flux-generated mass terms of the KK gauge fields associated with isometries of compactified subspaces is put down, correspondence of the "classical" KK approach and dual holography approach to the low-dimensional gauge theories is discussed, and idea of Bootstrap Holography is set forth.

hep-th↗

arXiv2008

BCS theory for finite size superconductors

We study finite size effects in superconducting metallic grains and determine the BCS order parameter and the low energy excitation spectrum in terms of size, and shape of the grain. Our approach combines the BCS self-consistency condition, a semiclassical expansion for the spectral density and interaction matrix elements, and corrections to the BCS mean-field. In chaotic grains mesoscopic fluctuations of the matrix elements lead to a smooth dependence of the order parameter on the excitation energy. In the integrable case we observe shell effects when e.g. a small change in the electron number leads to large changes in the energy gap.

cond-mat.supr-con↗

arXiv2007

Potential for the slow-roll inflation, mass scale hierarchy and Dark Energy from the Type IIA supergravity

The magnetic fluxbrane solution with a strongly warped throat is studied in the Type IIA supergravity theory with co-dimension one local source which surves as $Z_{2}$-symmetric UV boundary of the throat. Overall volume of extra space is stabilized since introduction of the local source breaks the no-scale structure of the theory and evades the no-go theorem. Radion field is defined as the position of UV boundary "moved" from its stable value fixed by the anisotropic Israel junction conditions. Analytical expression for the radion effective potential is received. Potential decreases exponentially (exponent is equal to 0,21 in Planck units) in the slow-roll region and apparently meets other demands of the early inflation. Reissner-Nordstrom type deformation of the elementary fluxbrane solution permits to construct the IR end of the throat and results in tiny positive non-zero value of the radion potential in its extremal point seen today as Dark Energy $ρ_{D.E.}$. Expressions for the mass scale hierarchy and for the "acceleration hierarchy" received in the paper give the physically interesting relation between two hierarchies: $ρ_{D.E.} \sim G_{N}^{2}m^{8}$.

hep-th↗

arXiv2005

String theory provides landmarks fixing RS branes' positions: Possibility to deduce large mass hierarchy from small numbers

Two-branes RS-I 5-dimensional model is generalized in higher dimensional string-induced theory with dilaton and $n$-form field. It is supposed that "hidden" and "visible" Randall-Sundrum branes are located at the boundaries of region of space-time where low-energy supergravity description is valid. This permits to determine mass scale hierarchy which calculated value proves to be strongly dependent on dimensionalities of subspaces.

hep-th↗

arXiv2005

Nonequilibrium Cooper pairing in the nonadiabatic regime

We obtain a complete solution for the mean-field dynamics of the BCS paired state with a large, but finite number of Cooper pairs in the non-adiabatic regime. We show that the problem reduces to a classical integrable Hamiltonian system and derive a complete set of its integrals of motion. The condensate exhibits irregular multi-frequency oscillations ergodically exploring the part of the phase-space allowed by the conservation laws. In the thermodynamic limit however the system can asymptotically reach a steady state.

cond-mat.supr-con↗

arXiv2005

Relaxation and persistent oscillations of the order parameter in the non-stationary BCS theory

We determine the limiting dynamics of a fermionic condensate following a sudden perturbation for various initial conditions. We demonstrate that possible initial states of the condensate fall into two classes. In the first case, the order parameter asymptotes to a constant value. The approach to a constant is oscillatory with an inverse square root decay. This happens, e.g., when the strength of pairing is abruptly changed while the system is in the paired ground state and more generally for any nonequilibrium state that is in the same class as the ground state. In the second case, the order parameter exhibits persistent oscillations with several frequencies. This is realized for nonequilibrium states that belong to the same class as excited stationary states. Our classification of initial states extends the concept of excitation spectrum to nonequilibrium regime and allows one to predict the evolution without solving equations of motion.

cond-mat.supr-con↗

arXiv2005

Integrable dynamics of coupled Fermi-Bose condensates

We study the mean-field dynamics of a fermionic condensate interacting with a single bosonic mode (a generalized Dicke model). This problem is integrable and can be mapped onto a corresponding BCS problem. We derive the general solution and a full set of integrals of motion for the time evolution of coupled Fermi-Bose condensates. The present paper complements our earlier study of the dynamics of the BCS model (cond-mat/0407501 and cond-mat/0505493). Here we provide a self-contained introduction to the variable separation method, which enables a complete analytical description of the evolution of the generalized Dicke, BCS, and other similar models.

cond-mat.supr-con↗

arXiv2005

Models of environment and T_1 relaxation in Josephson Charge Qubits

A theoretical interpretation of the recent experiments of Astafiev et. al. on the T_1-relaxation rate in Josephson Charge Qubits is proposed. The experimentally observed reproducible nonmonotonic dependence of T_1 on the splitting E_J of the qubit levels suggests further specification of the previously proposed models of the background charge noise. From our point of view the most promising is the ``Andreev fluctuator'' model of the noise. In this model the fluctuator is a Cooper pair that tunnels from a superconductor and occupies a pair of localized electronic states. Within this model one can naturally explain both the average linear T_1(E_J) dependence and the irregular fluctuations. The role of fluctuators in the formation of strong resonant peaks in this dependence is also discussed.

cond-mat.mes-hall↗

arXiv2004

II. Calculation of large mass hierarchy from number of extra dimensions

The higher-dimensional generalization of Randall-Sundrum approach with additional positive curvature $n$-dimensional and Ricci-flat $m$-dimensional compuct subspaces is considered in pure gravity theory with metric of space-time and $(p+1)$-form potential as basic fields. Introduction of mass term of $(p+1)$-form potential into the action of co-dimension one brane permits to stabilize brane's position and hence to calculate the value of Planck/electroweek scales ratio. There are no ad hoc too large or too small parameters in the theory; calculated mass hierarchy strongly depends on dimensionalities $m$, $n$ of additional subspaces and its observed large value in 4 dimensions (i.e. for $p=3$) is received in particular in $D13$ ($m=1$, $n=7$) or $D16$ ($m=2$, $n=9$) space-times.

hep-th↗

arXiv2004

I. Calculation of the observed value of large mass hierarchy in modified RS model

In generalized Randall-Sundrum (RS) model with dilaton where bulk potential is generated by the antisymmetric tensor field the mass term of this field is introduced into the brane's Action. This permits to stabilize brane's position and hence to calculate the Planck/electroweek scales ratio which proves to depend non-analytically on the dilaton-antisymmetric tensor field coupling constant. The large observed number of mass hierarchy is achieved for the moderate value of this coupling constant of order 0,3. In the subsequent Paper II it is shown that the same approach in a higher dimensional theory without dilaton permits to express mass hierarchy only through number of extra dimensions.

hep-th↗

arXiv2004

Solution for the dynamics of the BCS and central spin problems

We develop an explicit description of a time-dependent response of fermionic condensates to perturbations. The dynamics of Cooper pairs at times shorter than the energy relaxation time can be described by the BCS model. We obtain a general explicit solution for the dynamics of the BCS model. We also solve a closely related dynamical problem - the central spin model, which describes a localized spin coupled to a "spin bath". Here, we focus on presenting the solution and describing its general properties, but also mention some applications, e.g. to nonstationary pairing in cold Fermi gases and to the issue of electron spin decoherence in quantum dots. A typical dynamics of the BCS and central spin models is quasi-periodic with a large number of frequencies and stable under small perturbations. We show that for certain special initial conditions the number of frequencies decreases and the solution simplifies. In particular, periodic solutions correspond to the ground state and excitations of the BCS model.

cond-mat.supr-con↗

arXiv2004

Finite Size Corrections for the Pairing Hamiltonian

We study the effects of superconducting pairing in small metallic grains. We show that in the limit of large Thouless conductance one can explicitly determine the low energy spectrum of the problem as an expansion in the inverse number of electrons on the grain. The expansion is based on the formal exact solution of the Richardson model. We use this expansion to calculate finite size corrections to the ground state energy, Matveev-Larkin parameter, and excitation energies.

cond-mat.supr-con↗

arXiv2003

Strong Coupling Expansion for the Pairing Hamiltonian

The paper is devoted to the effects of superconducting pairing in small metallic grains. It turns out that at strong superconducting coupling and in the limit of large Thouless conductance one can explicitly determine the low energy spectrum of the problem. We start with the strong coupling limit and develop a systematic expansion in powers of the inverse coupling constant for the many-particle spectrum of the system. The strong coupling expansion is based on the formal exact solution of the Richardson model and converges for realistic values of the coupling constant. We use this expansion to study the low energy excitations of the system, in particular energy and spin gaps in the many-body spectrum.

cond-mat.str-el↗

arXiv2003

Extracting Hidden Symmetry from the Energy Spectrum

In this paper we revisit the problem of finding hidden symmetries in quantum mechanical systems. Our interest in this problem was renewed by nontrivial degeneracies of a simple spin Hamiltonian used to model spin relaxation in alkali-metal vapors. We consider this spin Hamiltonian in detail and use this example to outline a general approach to finding symmetries when eigenvalues and eigenstates of the Hamiltonian are known. We extract all nontrivial symmetries responsible for the degeneracy and show that the symmetry group of the Hamiltonian is SU(2). The symmetry operators have a simple meaning which becomes transparent in the limit of large spin. As an additional example we apply the method to the Hydrogen atom.

cond-mat↗

arXiv2003

Statistical Properties of The First Excited State of an Interacting Many Particle Disordered System

The distribution $P_1$ of the first many-body excitation energy of a weakly and moderately interacting electron gas in a finite conductor (in the diffusive regime) is calculated. As the interaction is increased, $P_1$ crosses over from Wigner-Dyson to Poisson. We characterize this transition through the inverse participation ratio in Hilbert space, and examine its manifestation in a projected 2-dimensional space.

cond-mat.dis-nn↗

arXiv2002

Ability to Count to Two. Opening Talk at the Third International Sakharov Conference on Physics

Third International Sakharov Conference on Physics organized by the Theoretical Physics Department of the Lebedev Institute, Russian Academy of Sciences, covered wide scope of topics: astrophysics, fusion, high field, high pressure and high density research, superstrings and dualities, brane world and quantum gravity, quantum field theory and high energy physics. This short Opening Word however exceeds the bounds of physics - it is about three "dynamical characteristics" of Sakharov's methodology and way of thinking: "Artseulov method", "a permanent feeling of possible personal error", and ability "to count to two", which in present days is not less demanded than before.

hep-ph↗

arXiv2002

Calculation of the Observationally Small Cosmological Constant in the Model of Six-Dimensional Warped Brane-Bolt World

In the 6-dimensional model of warped compactification based on the euclidean AdS Reissner-Nordstrom metric it is possible to escape artificial 4-brane's stress-energy tensor anistropy necessary for fulfillment of Israel junction conditions by introducing in 3+1 spacetime of the cosmological constant which turns out to be ${}\sim G^2$ ($G$ - Newton's constant) and acquires the value compatible with observations.

hep-th↗

arXiv2001

Calculation of dephasing times in closed quantum dots

Dephasing of one-particle states in closed quantum dots is analyzed within the framework of random matrix theory and Master equation. Combination of this analysis with recent experiments on the magnetoconductance allows for the first time to evaluate the dephasing times of closed quantum dots. These dephasing times turn out to depend on the mean level spacing and to be significantly enhanced as compared with the case of open dots. Moreover, the experimental data available are consistent with the prediction that the dephasing of one-particle states in finite closed systems disappears at low enough energies and temperatures.

cond-mat.mes-hall↗