arXiv subjects

G. E. Volovik

Publications and source records attributed to G. E. Volovik.

At least 55 records · Page 3Linked to original sources

arXiv2022

Macroscopic quantum tunneling: from quantum vortices to black holes and Universe

The paper has been prepared for the JETP issue, dedicated to the 95th anniversary of the birth of E.I. Rashba. E. Rashba stood at the origins of macroscopic quantum tunneling together with his colleagues from the Landau Institute S.V. Iordansky and A.M. Finkelshtein. They pave the way for studying macroscopic quantum tunneling in various systems. In this paper, this approach is extended to cosmological objects such as a black hole and de Sitter Universe. In particular, this allowed to calculate the entropy of Reissner-Nordström (RN) black hole with two horizons and the corresponding temperature of the thermal Hawking radiation. Several different approaches were used: the method of semiclassical tunneling for calculation of the Hawking temperature; the cotunneling mechanism -- the coherent sequence of tunneling at two horizons, each determined by the corresponding Hawking temperature; the method of singular coordinate transformations for calculations of macroscopic quantum tunneling from the RN black hole to the RN white hole; the method of the adiabatic change of the fine structure constant for the adiabatic transformation from the RN black hole to the Schwarzschild black hole; etc.

gr-qc↗

arXiv2022

Big bang as a topological quantum phase transition

It has been argued that a particular type of quantum-vacuum variable $q$ can provide a solution to the main cosmological constant problem and possibly also give a cold-dark-matter component. We now show that the same $q$-field may suggest a new interpretation of the big bang, namely as a quantum phase transition between topologically inequivalent vacua. These two vacua are characterized by the equilibrium values $q=\pm \, q_{0}$ and there is a kink-type solution $q(t)$ interpolating between $q=- q_{0}$ for $t\to -\infty$ and $q= +q_{0}$ for $t\to \infty$, with conformal symmetry for $q=0$ at $t=0$.

hep-th↗

arXiv2022

Quantum turbulence and Planckian dissipation

The notion of the Planckian dissipation is extended to the system of the Caroli-de Gennes-Matricon discrete energy levels in the vortex core of superconductors and fermionic superfluids. In this extension, the Planck dissipation takes place when the relaxation time $τ$ is comparable with the quantum Heisenberg time $t_H=\hbar/ΔE$, where $ΔE$ is the interlevel distance in the vortex core (the minigap). This type of Planck dissipation has two important physical consequences. First, it determines the regime, when the effect of the axial anomaly becomes important. The anomalous spectral flow of the energy levels along the chiral branch of the Caroli-de Gennes-Matricon states becomes important in the super-Planckian region, i.e. when $τ<\hbar/ΔE$. Second, the Planck dissipation separates the laminar flow of the superfluid liquid at $τ<\hbar/ΔE$ and the vortex turbulence regime at $τ>\hbar/ΔE$.

cond-mat.supr-con↗

arXiv2022

Negative Newton constant may destroy some conjectures

The magnitude and sign of the gravitational coupling $1/G$ depend on the relations between different contributions from scalar, fermionic and vector fields. In principle, this may give the zero and negative values of $1/G$ in some hypothetical Universes with the proper relations between the fermionic and bosonic species. We consider different conjectures related to gravity, such as the wave function collapse caused by gravity, entropic gravity, and maximum force. We find that some of them do not work in the Universes with zero or negative $1/G$, and thus cannot be considered as universal. Thus the extension of the gravitational coupling to $1/G \leq 0$ provides the test on the universality of the proposed theories of gravity.

gr-qc↗

arXiv2022

Vortices in polar and $β$ phases of $^3$He

Recently new topological phase of superfluid $^3$He has been discovered -- the $β$ phase, which is obtained by strong polarization of the nematic polar phase. We consider half-quantum vortices, which are formed in rotating cryostat, and discuss the evolution of the vortex lattice in the process of the transition from the polar phase to the $β$-phase via the spin-polarized polar phase.

cond-mat.other↗

arXiv2021

Gravity from symmetry breaking phase transition

The paper is devoted to the memory of Dmitry Diakonov. We discuss gravity emerging in the fermionic vacuum as suggested by Diakonov 10 years ago in his paper "Towards lattice-regularized Quantum Gravity". Gravity emerges in the phase transition. The order parameter in this transition is the tetrad field, which appears as the bilinear composite of the fermionic fields. This symmetry breaking gives 6 Nambu-Goldstone modes; 6 gauge bosons in the spin-connection fields, which absorb 6 NG modes and become massive gauge bosons; and 6 Higgs fields. The similar scenario of the symmetry breaking with appearance of the $5+1$ Higgs gravitons takes place in the B-phase of superfluid $^3$He. While in $^3$He-B these Higgs modes are all massive, in the GR these Higgs collective modes give rise to two massless gravitational waves.

gr-qc↗

arXiv2021

Anomalous chiral transport with vorticity and torsion: Cancellation of two mixed gravitational anomaly currents in rotating chiral $p+ip$ Weyl condensates

Relativistic gravitational anomalies lead to anomalous transport coefficients that can be activated at finite temperature in condensed matter systems with gapless fermions. The chiral vortical effect (CVE) is an anomalous chiral current along a rotation axis, expressed in terms of a gravimagnetic field and a gravitational anomaly. Another one, the chiral torsional effect (CTE), arises from hydrodynamically independent frame fields and connection. We discuss the relation of CVE, CTE and gravitational anomalies for relativistic fermions from the perspective of torsion and the Nieh-Yan anomaly. The DC transport coefficients of the two anomalies are found to be closely related depending whether or not torsion is non-zero in the hydrodynamics. The relativistic anomaly from torsion is well defined if instead of an ultraviolet divergent term, the chemical potential or temperature enter. The anomaly term is 2nd order in gradients and contributes in linear response for CTE, implying also the same for CVE. As an example, we consider chiral $p+ip$ Weyl superfluids/conductors. At low-energies, the system is effectively relativistic along a special anisotropy axis. The hydrodynamics is governed by two velocities, normal velocity $\boldsymbol{v}_n$ and superfluid velocity $\boldsymbol{v}_s$. The two anomalies follow from the normal component rotation and the dependence of the momentum density on the superfluid velocity (order parameter). In the CVE the chiral current is produced by solid body rotation of the normal component with (angular) velocity $\boldsymbol{v}_n= \boldsymbolΩ\times \boldsymbol{r}$. In the CTE, a chiral current is produced the vorticity $\nabla \times \boldsymbol{v}_s$, which in the low-energy effective theory is torsion. In equilibrium, $\langle\langle \nabla \times \boldsymbol{v_s}\rangle\rangle= 2\boldsymbolΩ$ on average and the two anomaly currents cancel.

cond-mat.supr-con↗

arXiv2021

Combined Lorentz symmetry: lessons from superfluid 3He

We consider the possibility of the scenario in which the $P$, $T$ and Lorentz symmetry of the relativistic quantum vacuum are all the combined symmetries. These symmetries emerge as a result of the symmetry breaking of the more fundamental $P$, $T$ and Lorentz symmetries of the original vacuum, which is invariant under separate groups of the coordinate transformations and spin rotations. The condensed matter vacua (ground states) suggest two possible scenarios of the origin of the combined Lorentz symmetry, both are realized in the superfluid phases of liquid $^3$He: the $^3$He-A scenario and the $^3$He-B scenario. In these scenarios the gravitational tetrads are considered as the order parameter of the symmetry breaking in the quantum vacuum. The $^3$He-B scenarios applied to the Minkowski vacuum leads to the continuous degeneracy of the Minkowski vacuum with respect to the $O(3,1)$ spin rotations. The symmetry breaking leads to the corresponding topological objects, which appear due to the nontrivial topology of the manifold of the degenerate Minkowski vacua, such as torsion strings. The 4-fold degeneracy of the Minkowski vacuum with respect to discrete $P$ and $T$ symmetries suggests that the Weyl fermions are described by four different tetrad fields: the tetrad for the left-handed fermions, the tetrad for the right-handed fermions, and the tetrads for their antiparticles. This may lead to the gravity with several metric fields, so that the parity violation may lead to the breaking of equivalence principle. Finally we considered the application of the gravitational tetrads for the solution of the cosmological constant problem.

gr-qc↗

arXiv2021

Effect of the inner horizon on the black hole thermodynamics: Reissner-Nordström black hole and Kerr black hole

For the Schwarzschild black hole the Bekenstein-Hawking entropy is proportional to the area of the event horizon. For the black holes with two horizons the thermodynamics is not very clear, since the role of the inner horizons is not well established. Here we calculate the entropy of the Reissner-Nordström black hole and of the Kerr black hole, which have two horizons. For the spherically symmetric Reissner-Nordström black hole we used several different approaches. All of them give the same result for the entropy and for the corresponding temperature of the thermal Hawking radiation. The entropy is not determined by the area of the outer horizon, and it is not equal to the sum of the entropies of two horizons. It is determined by the correlations between the two horizons, due to which the total entropy of the black hole and the temperature of Hawking radiation depend only on mass $M$ of the black hole and do not depend on the black hole charge $Q$. For the Kerr and Kerr-Newman black holes it is shown that their entropy has the similar property: it depends only on mass $M$ of the black hole and does not depend on the angular momentum $J$ and charge $Q$.

gr-qc↗

arXiv2021

Type-II Weyl semimetal vs gravastar

The boundary between the type I and type II Weyl semimetals serves as the event horizon for the "relativistic" fermions. The interior of the black hole is represented by the type II Weyl semimetal, where the Fermi surface is formed. The process of the filling of the Fermi surface by electrons results in the relaxation inside the horizon. This leads to the Hawking radiation and to the reconstruction of the interior vacuum state. After the Fermi surface is fully occupied, the interior region reaches the equilibrium state, for which the Hawking radiation is absent. If this scenario is applicable to the real black hole, then the final state of the black hole will be the dark energy star with the event horizon. Inside the event horizon one would have de Sitter space time, which is separated from the event horizon by the shell of the Planck length width. Both the de Sitter part and the shell are made of the vacuum fields without matter. This is distinct from the gravastar, in which the matter shell is outside the "horizon", and which we call the type I gravastar. But this is similar to the other type of the vacuum black hole, where the shell is inside the event horizon, and which we call the type II gravastar. We suggest to study the vacuum structure of the type II gravastar using the $q$-theory, where the vacuum variable is the 4-form field introduced for the phenomenological description of the quantum vacuum.

gr-qc↗

arXiv2021

Suppressing the Kibble-Zurek mechanism by a symmetry-violating bias

The formation of topological defects in continuous phase transitions is driven by the Kibble-Zurek mechanism. Here we study the formation of single- and half-quantum vortices during transition to the polar phase of $^3$He in the presence of a symmetry-breaking bias provided by the applied magnetic field. We find that vortex formation is suppressed exponentially when the length scale associated with the bias field becomes smaller than the Kibble-Zurek length. We thus demontrate an experimentally feasible shortcut to adiabaticity -- an important aspect for further understanding of phase transitions as well as for engineering applications such as quantum computers or simulators.

cond-mat.other↗

arXiv2021

Double Hawking temperature in de Sitter Universe and cosmological constant problem

As distinct from the black hole physics, the de Sitter thermodynamics is not determined by the cosmological horizon, the effective temperature differs from the Hawking temperature. In particular, the atom in the de Sitter universe experiences thermal activation corresponding to the local temperature, which is twice larger than the Hawking temperature, $T_{\rm loc}=2T_{\rm Hawking}$. The same double Hawking temperature describes the decay of massive scalar field in the de Sitter universe. The reason, why the local temperature is exactly twice the Hawking temperature, follows from the geometry of the de Sitter spacetime. The weakening of the role of the cosmological horizon in de Sitter universe is confirmed by considering Hawking radiation. We discuss the difference between the radiation of particles in the de Sitter spacetime and the Schwinger pair creation in the electric field. We use the stationary Painleve-Gullstrand metric for the de Sitter spacetime, where the particles are created by Hawking radiation from the cosmological horizon, and time independent gauge for the electric field. In these stationary frames the Hamiltonians and the energy spectra of massive particles look rather similar. However, the final results are essentially different. In case of Schwinger pair production the number density of the created pairs grows with time, while in the de Sitter vacuum the number density of the created pairs is finite. The latter suggests that Hawking radiation from the cosmological horizon does not lead to instability of the de Sitter vacuum. The other mechanisms of instability are required for the dynamical solution of the cosmological constant problem. We consider the possible role of the local temperature $T_{\rm loc}=2T_{\rm H}$ in the decay of the de Sitter space-time due to the energy exchange between the vacuum energy and relativistic matter with this temperature.

gr-qc↗

arXiv2021

From black hole to white hole via the intermediate static state

We discuss the macroscopic quantum tunneling from the black hole to the white hole of the same mass. Previous calculations in Ref.[1] demonstrated that the probability of the tunneling is $p \propto \exp(-2S_\text{BH})$, where $S_\text{BH}$ is the entropy of the Schwarzschild black hole. This in particular suggests that the entropy of the white hole is with minus sign the entropy of the black hole, $S_\text{WH}(M)=- S_\text{BH}(M)= - A/(4G)$. Here we use a different way of calculations. We consider three different types of the hole objects: black hole, white hole and the fully static intermediate state. The probability of tunneling transitions between these three states is found using singularities in the coordinate transformations between these objects. The black and white holes are described by the Painleve-Gullstrand coordinates with opposite shift vectors, while the intermediate state is described by the static Schwarzschild coordinates. The singularities in the coordinate transformations lead to the imaginary part in the action, which determines the tunneling exponent. For the white hole the negative entropy is obtained, while the intermediate state -- the fully static hole -- has zero entropy. This procedure is extended to the Reissner-Nordström black hole and to its white and static partners, and also to the entropy and temperature of the de Sitter Universe.

physics.gen-ph↗

arXiv2021

Negative temperature: further extensions

This paper is motivated by the recent paper M. Baldovin, S. Iubini, R. Livi and A. Vulpiani, Statistical mechanics of systems with negative temperature, arXiv:2103.12572. The authors suggest that negative absolute temperatures are consistent with equilibrium thermodynamics. This is correct, if the environment also has negative temperature. Otherwise such states represent the transient though maybe long-lived metastable effects. Here we consider the extension of the negative temperatures to the relativistic systems. We show that the negative state is possible in the Dirac vacuum, which is obtained by the $PT$ symmetry transformation from the conventional Dirac sea. If such vacuum with inverse population fills the whole Universe, its thermodynamics determined by negative temperatures becomes equilibrium.

gr-qc↗

arXiv2021

Analog of gravitational anomaly in topological chiral superconductors

It is known that the contribution of torsion to the equation for the chiral Weyl fermions can be equivalently considered in terms of the axial $U(1)$ gauge field. In this scenario the gravitational field transforms to the $U(1)$ gauge field. Here we show that in chiral superconductors the opposite scenario takes place: the electromagnetic $U(1)$ field serves as the spin connection for the Bogoliubov fermionic quasiparticles. As a result the electromagnetic field gives rise to the gravitational anomaly, which contains the extra factor $1/3$ in the corresponding Adler-Bell-Jackiw equation as compared with the conventional chiral anomaly. We also consider the gravitational anomaly produced in neutral Weyl superfluids by the analog of the gravitational instanton, the process of creation and annihilation of the 3D topological objects -- hopfions. The gravitational instanton leads to creation of the chiral charge.

cond-mat.supr-con↗

arXiv2020

Topological polarization, dual invariants, and surface flat band in crystalline insulators

We describe a three-dimensional crystalline topological insulator (TI) phase of matter that exhibits spontaneous polarization. This polarization results from the presence of (approximately) flat bands on the surface of such TIs. These flat bands are a consequence of the bulk-boundary correspondence of polarized topological media, and contrary to related nodal line semimetal phases also containing surface flat bands, they span the entire surface Brillouin zone. We also present an example Hamiltonian exhibiting a Lifshitz transition from the nodal line phase to the TI phase with polarization. Utilizing elasticity tetrads, we show a complete classification of 3D crystalline TI phases and invariants. The phase with polarization naturally arises from this classification as a dual to the previously better-known 3D TI phase exhibiting quantum (spin) Hall effect. Besides polarization, another implication of the large surface flat band is the susceptibility to interaction effects such as superconductivity: the mean-field critical temperature is proportional to the size of the flat bands, and this type of systems may hence exhibit superconductivity with a very high critical temperature.

cond-mat.mtrl-sci↗

arXiv2020

$^3$He Universe 2020

The latest news from $^3$He Universe are presented together with the extended map of the Universe.

cond-mat.other↗

arXiv2020

Vielbein with mixed dimensions and gravitational global monopole in the planar phase of superfluid $^3$He

The planar phase of superfluid $^3$He has Dirac points in momentum space and the analog of Dirac monopole in the real space. Here we discuss the combined effect of Dirac point and Dirac monopole. It is shown that in the presence of the monopole the effective metric acting on Dirac fermions corresponds to the metric produced by the global monopole in general relativity: it is the conical metric. Another consequence is that the primary variable, which gives rise to the effective metric, is the unusual vielbein field in the form of the $4\times 5$ matrix, as distinct from the conventional $4\times 4$ matrix of the tetrad field in tetrad gravity.

cond-mat.other↗