arXiv subjects

Rajat K Chaudhuri

Publications and source records attributed to Rajat K Chaudhuri.

9 recordsLinked to original sources

arXiv2007

A new formulation of the relativistic many-body theory of electric dipole moments of closed shell atoms

The electric dipole moments of closed-shell atoms are sensitive to the parity and time-reversal violating phenomena in the nucleus. The nuclear Schiff moment is one such property, it arises from the parity and time reversal violating quark-quark interactions and the quark-chromo electric dipole moments. We calculate the electric dipole moment of atomic $^{199}{\rm Hg}$ arising from the nuclear Schiff moment using the relativistic coupled-cluster theory. This is the most accurate calculation of the quantity to date. Our calculations in combination with the experiment data provide important insights to the P and T violating coupling constants at the elementary particle level. In addition, a new limit on the tensor-pseudo tensor induced atomic EDM, calculated using the relativistic coupled-cluster theory is also presented.

physics.atom-ph↗

arXiv2007

A relativistic unitary coupled-cluster study of electric quadrupole moment and magnetic dipole hyperfine constants of ^{199}Hg^{+}

Searching for an accurate optical clock which can serve as a better time standard than the present day atomic clock is highly demanding from several areas of science and technology. Several attempts have been made to built more accurate clocks with different ion species. In this article we discuss the electric quadrupole and hyperfine shifts in the $5d^{9}6s^{2} ^{2}D_{5/2}(F=0,m_{F}=0)\leftrightarrow5d^{10}6s ^{2}S_{1/2}(F=2,m_{F}=0)$ clock transition in $ ^{199}Hg^{+}$, one of the most promising candidates for next generation optical clocks. We have applied Fock-space unitary coupled-cluster (FSUCC) theory to study the electric quadrupole moment of the $5d^{9}6s^{2} ^{2}D_{5/2}$ state and magnetic dipole hyperfine constants of $5d^{9}6s^{2} ^{2}D_{3/2,5/2}$ and $5d^{10}6s^{1} ^{2}S_{1/2}$ states respectively of $ ^{199}Hg^{+}$. We have also compared our results with available data. To the best of our knowledge, this is the first time a variant of coupled-cluster (CC) theories has been applied to study these kinds of properties of $Hg^{+}$and is the most accurate estimate of these quantities to date.

physics.atom-ph↗

arXiv2007

Effects of partial triple excitations in atomic coupled cluster calculations

In this article we study the effects of higher body excitations in the relativistic CC calculations for atoms and ions with one valence electron using Fock-space CCSD, CCSD(T) and its unitary variants. The present study demonstrates that CCSD(T) estimates the ionization potentials (IPs) and the valence electron removal energies quite accurately for alkali atoms and singly ionized alkaline earth ions, but yields unphysical energy levels for atoms and/or ions with partially filled sub-shell like C II. We further demonstrate that the higher body excitation effects can be incorporated more effectively through the unitary coupled cluster theory (UCC) compared to the CCSD(T) method.

physics.atom-ph↗

arXiv2007

Branching ratios of radiative transitions in O VI

We study the branching ratios of the allowed and forbidden radiative transitions among the first few (9) fine structure levels of O VI using relativistic coupled cluster theory. We find irregular patterns for a number of transitions with in $n$-complexes with $n\le4$. We have used the exisiting values of the allowed electric dipole ($E1$) transition as a benchmark of our theory. Good agreement with the existing values establish accuracies of not only the theoretical method but the basis function as well. In general the electric quadrupole ($E2$) transition probabilities are greater in magnitude than magnetic dipole ($M1$) transition probabilities, whereas for medium atomic transition frequencies they are of the same order of magnitude. On the other hand if the transitions involved are between two fine structure components of the same term, then the $M1$ transition probability is more probable than that of $E2$. We have analyzed these trends with physical arguments and order of magnitude estimations. The results presented here in tabular and graphical forms are compared with the available theoretical and observed data. Graphical analysis helps to understand the trends of electric and magnetic transitions for the decay channels presented here. Our calculated values of the lifetimes of the excited states are in very good agreement with the available results.

physics.atom-ph↗

arXiv2007

Relativistic multi-reference Fock-space coupled-cluster calculation of the forbidden $6s^2^1 S_0 \longrightarrow 6s5d^3 D_1$ magnetic-dipole transition in ytterbium

We report the forbidden $6s^{2} ^{1}S_{0}\longrightarrow6s5d ^{3}D_{1}$ magnetic-dipole transition amplitude computed using multi-reference Fock-space coupled-cluster theory. Our computed transition matrix element ($1.34\times10^{-4}μ_{B}$) is in excellent agreement with the experimental value ($1.33\times10^{-4}$ $μ_{B}$). This value in combination with other known quantities will be helpful to determine the parity non-conserving amplitude for the $6s^{2} ^{1}S_{0}\longrightarrow6s5d ^{3}D_{1}$ transition in atomic Yb. To our knowledge our calculation is the most accurate to date and can be very important in the search of physics beyond the standard model. We further report the $6s6p ^{3}P_{0}\longrightarrow6s6p ^{1}P_{1}$ and $6s5d ^{3}D_{1}\longrightarrow6s6p ^{3}P_{0}$ transition matrix elements which are also in good agreement with the earlier theoretical estimates.

physics.atom-ph↗

arXiv2005

Relativistic and correlation effects in atoms

This review article deals with some case studies of relativistic and correlation effects in atomic systems. After a brief introduction to relativistic many-electron theory, a number of applications ranging from correlation energy to parity non-conservation in atoms are considered. There is a special emphasis on relativistic coupled-cluster theory as most of the results presented here are based on it.

physics.atom-ph↗

arXiv2005

Relativistic unitary coupled cluster theory and applications

We present the first formulation and application of relativistic unitary coupled cluster theory to atomic properties. The remarkable features of this theory are highlighted, and it is used to calculate the lifetimes of $5^{2}D_{3/2}$ and $6^{2}P_{3/2}$ states of $Ba^{+}$ and $Pb^{+}$ respectively. The results clearly suggest that it is very well suited for accurate \emph{ab initio} calculations of properties of heavy atomic systems.

physics.atom-ph↗

arXiv2004

Comparative studies of the magnetic dipole and electric quadrupole hyperfine constants for the ground and low lying excited states of ^{25}Mg^{+}

We have employed the relativistic coupled cluster theory to calculate the magnetic dipole and electric quadrupole hyperfine constants for the ground and low lying excited states of singly ionized magnesium. Comparison with experimental and the other theoretical results are done and predictions are also made for a few low lying excited states which could be of interest. We have made comparative studies of the important many body effects contributing to the hyperfine constants for the different states of the ion.

physics.atom-ph↗

arXiv2004

Accurate calculations of magnetic dipole and electric quadrupole hyperfine coupling constants of 6 P_{3/2} state of Cesium atom : A Relativistic Coupled Cluster approach

We report the magnetic dipole and electric quadrupole hyperfine coupling constants of 6 P_{3/2} state of ^{133} Cs(I= {7/2}) obtained from the relativistic coupled cluster (RCC) method. To our knowledge, no prior electric quadrupole hyperfine CC calculation is available for ^{133} Cs(6 P_{3/2}) state. Our computed magnetic dipole (A) and electric quadrupole (B) coupling constants are in excellent agreement with the experiment.

physics.atom-ph↗