arXiv subjects

Y. Koohsarian

Publications and source records attributed to Y. Koohsarian.

9 recordsLinked to original sources

arXiv2019

On the high temperature limit of the Casimir energy

We introduce a useful approach to find asymptotically explicit expressions for the Casimir free energy at large temperature. The resulting expressions contain the classical terms as well as the few first terms of the corresponding heat-kernel expansion, as expected. This technique works well for many familiar configurations in Euclidean as well as non-Euclidean spaces. By utilizing this approach, we provide some new numerically considerable results for the Casimir pressure in some rectangular ideal-metal cavities. For instance, we show that at sufficiently large temperature, the Casimir pressure acting on the sidewalls of a rectangular tube can be up to twice that of the two parallel planes. We also apply this technique for calculating the Casimir free energy on a 3-torus as well as a 3-sphere. We show that a nonzero mass term for both scalar and spinor fields as well on the torus as on the sphere, violates the third law of thermodynamics. We obtain some negative values for the Casimir entropy on the 3-torus as well as on the 3-sphere. We speculate that these negative Casimir entropies can be interpreted thermodynamically as an instability of the vacuum state at finite temperatures

hep-th↗

arXiv2018

Phononic Casimir corrections for Graphene resonator

By calculating a Casimir energy for the acoustic phonons of Graphene, we find some temperature-dependent corrections for the pretension of a Graphene sheet suspended on a trench. We obtain values of the order of few mN/m for these corrections in fully as well as doubly clamped Graphene on a narrow trench with one nanometer width, at room temperature. These values are considerable compared to the experimental values, and can increase the fundamental resonance frequency of the Graphene. The values of these corrections increase by increasing the temperature, and so they can be utilized for tuning the Graphene pretension.

cond-mat.mes-hall↗

arXiv2017

Casimir energy for acoustic phonons in graphene

We find the Casimir energy, at finite temperature, for acoustic phonons in a Graphene sheet suspended over a rectangular trench, and the corresponding Casimir forces are interpreted as correction terms to the built-in tensions of the Graphene. We show that these corrections generally break the tensional isotropy of the membrane, and can increase or decrease the membrane tension. We demonstrate that for a narrow rectangular trench with side-lengths in the order of few nanometers and few micrometers, these temperature corrections are expected to be noticeable ($\sim 10^{-4} N/m$) at the room temperature. These corrections would be even more considerable by increasing the temperature, and can be applied for adjusting the built-in tension of the Graphene. Consequently we introduce a corrected version for the fundamental resonance frequency of the Graphene resonator.

cond-mat.mes-hall↗

arXiv2017

Casimir temperature correction to the Bosonic string mass

Through the Casimir effect, we obtain a temperature correction to the ground state mass of the Bosonic string. Accordingly, we show that higher than the temperature $\approx 1/2π$, the Tachyon attain real mass, and also we find massive Graviton for nonzero temperatures. As another consequence, we demonstrate that for temperatures higher than the Hagedorn temperature, the string would find again a Tachyonic state.

hep-th↗

arXiv2017

Fermionic Casimir effect in Graphene

We investigate the Fermionic Casimir effect at finite temperature for two parallel chain of adatoms in a Graphene sheet, and the corresponding Casimir force is interpreted as an interaction between the adatom chains. We apply useful techniques to find asymptotically explicit expressions for the Casimir energy, for small as well as large temperatures (with respect to the effective temperature of the Graphene). We obtain a value in the order of $10^{-2} N/m$ for the Casimir force between (per unit length of) the adatom chains being one nanometer apart, which is considerably noticeable e.g. in comparison to the experimental values for built-in tension of a suspended Graphene sheet.

cond-mat.mes-hall↗

arXiv2017

A temperature correction to the tachyon, using the Casimir effect

We find the free energy of the string by applying the known Matsubara formalism. Then through the Casimir effect we offer a temperature correction to the tachyon mass of the string. We see that for the fermionic part the temperature correction is precisely the opposite of that of bosonic part, so the quantum ground state of the superstring would remain massless, as expected.

hep-th↗

arXiv2017

Quantum vacuum effects for a massive Bosonic string in background B-field

We study the Casimir effect for a bosonic string extended between D-branes, and living in a flat space with an antisymmetric background B-field. We find the Casimir energy as a function of theB-field, and the mass-parameter of the string, and accordingly we obtain a B-dependence correction term to the ground-state mass of the string. We show that for sufficiently large B-field, the ground state of the string contains real (i.e. non-Tachyonic) particles.

hep-th↗

arXiv2014

Casimir-like corrections to the classical tensions of the strings and membranes

We find the Casimir-like energies for strings and membranes. We show that the related Casimir forces can be interpreted as quantum corrections to the classical tensions of the strings and membranes. We see that these corrections always increase the tensions of the circular string as well as spherical membrane, while for the straight string, rectangular and cylindrical membranes, these Casimir forces may increase or decrease the tensions. So we find that the quantum vacuum can break the (tensional) isotropy of the rectangular and cylindrical membranes. Also obtaining the nonzero-temperature Casimir energy, we find relations for the tensions at nonzero temperature.

hep-th↗

arXiv2012

Symplectic Quantization of Massive Bosonic string in background B-field

We give the details of symplectic quantization for a system containing second class constraints. This method is appropriate for imposing infinite series of constraints due to the boundary conditions. We use this method for massive bosonic strings in a background B-field and find the correct expansions of the fields in terms of the physical modes. We have found a canonical basis for this model.

hep-th↗