arXiv subjects

Ariel R. Zhitnitsky

Publications and source records attributed to Ariel R. Zhitnitsky.

At least 37 records · Page 2Linked to original sources

arXiv2013

Topological Casimir effect in Maxwell Electrodynamics on a Compact Manifold

We study the Topological Casimir effect, in which extra vacuum energy emerges as a result of the topological features of the theory, rather than due to the conventional fluctuations of the physical propagating degrees of freedom. We compute the corresponding topological term in quantum Maxwell theory defined on a compact manifold. Numerically, the topological effect is much smaller than the conventional Casimir effect. However, we argue that the Topological Casimir Effect is highly sensitive to an external magnetic field, which may help to discriminate it from the conventional Casimir effect. It is quite amazing that the external magnetic field plays the role of the $θ$ state, similar to a $θ$ vacuum in QCD, or $θ=π$ in topological insulators.

hep-th↗

arXiv2013

Long range order in gauge theories. Deformed QCD as a toy model

We study a number of different ingredients, related to long range order observed in lattice QCD simulations, using a simple "deformed QCD" model. This model is a weakly coupled gauge theory, which however has all the relevant crucial elements allowing us to study difficult and nontrivial problems which are known to be present in real strongly coupled QCD. In the present study, we want to understand the physics of long range order in form of coherent low dimensional vacuum configurations observed in Monte Carlo lattice simulations. We demonstrate the presence of double-layer domain wall structures in the deformed QCD, and study their interaction with localized topological monopoles. Furthermore, we show that there is in fact an attractive interaction between the two, such that the monopole favors a position within the domain wall.

hep-ph↗

arXiv2012

Topological Susceptibility and Contact Term in QCD. A Toy Model

We study a number of different ingredients related to $θ$ dependence, the non-dispersive contribution in topological susceptibility with the "wrong" sign, topological sectors in gauge theories, and related subjects using a simple "deformed QCD". This model is a weakly coupled gauge theory, which however has all the relevant essential elements allowing us to study difficult and nontrivial questions which are known to be present in real strongly coupled QCD. Essentially we want to test the ideas related to the $U(1)_A$ problem in a theoretically controllable manner using the "deformed QCD" as a toy model. One can explicitly see microscopically how the crucial elements work.

hep-th↗

arXiv2012

Casimir scaling in gauge theories with a gap. Deformed QCD as a toy model

We study a Casimir-like behaviour in a "deformed QCD". We demonstrate that for the system defined on a manifold of size L the difference Delta E between the energies of a system in a non-trivial background and Minkowski space-time geometry exhibits the Casimir-like scaling Delta E \sim L^{-1}, despite the presence of a mass gap in the system, in contrast with naive expectation Delta E \sim \exp(-m L), which would normally originate from any physical massive propagating degrees of freedom consequent to conventional dispersion relations. The Casimir-like behaviour in our system comes instead from a non-dispersive ("contact") term which is not related to any physical propagating degrees of freedom, such that the naive argument is simply not applicable. These ideas can be explicitly tested in weakly coupled deformed QCD. We comment on profound consequences for cosmology of this effect if it persists in real strongly coupled QCD.

hep-ph↗

arXiv2012

P odd fluctuations and Long Range Order in Heavy Ion Collisions. Deformed QCD as a Toy Model

We study the local violation of P and CP invariance in heavy ion collisions as observed at RHIC and LHC using a simple "deformed QCD" model. This model is a weakly coupled gauge theory, which however has all the relevant crucial elements allowing us to study difficult and nontrivial questions which are known to be present in real strongly coupled QCD. Essentially, we want to understand the physics of long range order in form of coherent low dimensional vacuum configurations observed in Monte Carlo lattice simulations. Apparently precisely such kind of configurations are responsible for sufficiently strong intensity of asymmetries observed in heavy ion collisions.

hep-ph↗

arXiv2012

Contact Term, its Holographic Description in QCD and Dark Energy

In this work we study the well known contact term, which is the key element in resolving the so-called $U(1)_A$ problem in QCD. We study this term using the dual Holographic Description. We argue that in the dual picture the contact term is saturated by the D2 branes which can be interpreted as the tunnelling events in Minkowski space-time. We quote a number of direct lattice results supporting this identification. We also argue that the contact term receives a Casimir -like correction $\sim (\Lqcd R)^{-1}$ rather than naively expected $\exp(-\Lqcd R)$ when the Minkowski space-time ${\cal R}_{3,1}$ is replaced by a large but finite manifold with a size $R$. Such a behaviour is consistent with other QFT-based computations when power like corrections are due to nontrivial properties of topological sectors of the theory. In holographic description such a behaviour is due to massless Ramond-Ramond (RR) field living in the bulk of multidimensional space when power like corrections is a natural outcome of massless RR field. In many respects the phenomenon is similar to the Aharonov -Casher effect when the "modular electric field" can penetrate into a superconductor where the electric field is exponentially screened. The role of "modular operator" from Aharonov -Casher effect is played by large gauge transformation operator $\cal{T}$ in 4d QCD, resulting the transparency of the system to topologically nontrivial pure gauge configurations. We discuss some profound consequences of our findings. In particular, we speculate that a slow variation of the contact term in expanding universe might be the main source of the observed Dark Energy.

hep-ph↗

arXiv2012

Local P Violation Effects and Thermalization in QCD: Views from Quantum Field Theory and Holography

We argue that the local violation of P and CP invariance in heavy ion collisions and the universal thermal aspects observed in high energy collisions are in fact two sides of the same coin, and both are related to quantum anomalies of QCD. We argue that the low energy relations representing the quantum anomalies of QCD are saturated by coherent low dimensional vacuum configurations as observed in Monte Carlo lattice studies. The thermal spectrum and approximate universality of the temperature with no dependence on energy of colliding particles in this framework is due to the fact that the emission results from the distortion of these low dimensional vacuum sheets rather than from the colliding particles themselves. The emergence of the long- range correlations of P odd domains (a feature which is apparently required for explanation of the asymmetry observed at RHIC and LHC) is also a result of the same distortion of the QCD vacuum configurations. We formulate the corresponding physics using the effective low energy effective Lagrangian. We also formulate the same physics in terms of the dual holographic picture when low-dimensional sheets of topological charge embedded in 4d space, as observed in Monte Carlo simulations, are identified with D2 branes. Finally, we argue that study of these long range correlations in heavy ion collisions could serve as a perfect test of a proposal that the observed dark energy in present epoch is a result of a tiny deviation of the QCD vacuum energy in expanding universe from its conventional value in Minkowski spacetime.

hep-ph↗

arXiv2011

Entropy, Contact Interaction with Horizon and Dark Energy

We present some arguments suggesting that the mismatch between Bekenstein- Hawking entropy and the entropy of entanglement for vector fields is due to the same gauge configurations which saturate the contact term in topological susceptibility in QCD. In both cases the extra term with a "wrong sign" is due to distinct topological sectors in gauge theories. This extra term has non-dispersive nature, can not be restored from conventional spectral function through dispersion relations, and can not be associated with any physical propagating degrees of freedom. We make few comments on some profound consequences of our findings. In particular, we speculate that the source of the observed dark energy may also be related to the same type of gauge configurations which are responsible for the mismatch between black hole entropy and the entropy of entanglement in the presence of causal horizon.

hep-th↗

arXiv2011

The Parity Odd Universe, Dark Energy and QCD

Cosmological observations on the largest scales exhibit a solid record of unexpected anomalies and alignments, apparently pointing towards a large scale violation of statistical isotropy. These include a variety of CMB measurements, as well as alignments of quasar polarisation vectors. In this paper we explore the possibility that several of the aforementioned large scale correlations are in fact not independent, and can be understood in a coherent way within the framework of a parity odd local Universe, and ultimately related to the nature of Dark Energy and its interactions with light.

astro-ph.CO↗

arXiv2011

P and CP Violation and New Thermalization Scenario in Heavy Ion Collisions

The violation of local P and CP invariance in QCD, as it is observed at RHIC, has been a subject of intense discussions for the last couple of years.Separately, a new thermalization scenario for heavy ion collisions through the event horizon as a manifestation of the Unruh effect, has been also suggested. In this paper we argue that these two, naively unrelated phenomena, are actually two sides of the same coin as they are deeply rooted into the same fundamental physics related to some very nontrivial topological features of QCD. We formulate the universality conjecture for P and CP odd effects in heavy ion collisions analogous to the universal thermal behaviour observed in all other high energy interactions.

nucl-th↗

arXiv2010

The Gauge Fields and Ghosts in Rindler Space

We consider 2d Maxwell system defined on the Rindler space with metric ds^2=\exp(2aξ)\cdot(dη^2-dξ^2) with the goal to study the dynamics of the ghosts. We find an extra contribution to the vacuum energy in comparison with Minkowski space time with metric ds^2= dt^2-dx^2. This extra contribution can be traced to the unphysical degrees of freedom (in Minkowski space). The technical reason for this effect to occur is the property of Bogolubov's coefficients which mix the positive and negative frequencies modes. The corresponding mixture can not be avoided because the projections to positive -frequency modes with respect to Minkowski time t and positive -frequency modes with respect to the Rindler observer's proper time ηare not equivalent. The exact cancellation of unphysical degrees of freedom which is maintained in Minkowski space can not hold in the Rindler space. In BRST approach this effect manifests itself as the presence of BRST charge density in L and R parts. An inertial observer in Minkowski vacuum |0> observes a universe with no net BRST charge only as a result of cancellation between the two. However, the Rindler observers who do not ever have access to the entire space time would see a net BRST charge. In this respect the effect resembles the Unruh effect. The effect is infrared (IR) in nature, and sensitive to the horizon and/or boundaries. We interpret the extra energy as the formation of the "ghost condensate" when the ghost degrees of freedom can not propagate, but nevertheless do contribute to the vacuum energy. Exact computations in this simple 2d model support the claim made in [1] that the ghost contribution might be responsible for the observed dark energy in 4d FLRW universe.

gr-qc↗

arXiv2010

The Electrosphere of Macroscopic "Quark Nuclei": A Source for Diffuse MeV Emissions from Dark Matter

Using a Thomas-Fermi model, we calculate the structure of the electrosphere of the quark antimatter nuggets postulated to comprise much of the dark matter. This provides a single self-consistent density profile from ultrarelativistic densities to the nonrelativistic Boltzmann regime that use to present microscopically justified calculations of several properties of the nuggets, including their net charge, and the ratio of MeV to 511 keV emissions from electron annihilation. We find that the calculated parameters agree with previous phenomenological estimates based on the observational supposition that the nuggets are a source of several unexplained diffuse emissions from the Galaxy. As no phenomenological parameters are required to describe these observations, the calculation provides another nontrivial verification of the dark-matter proposal. The structure of the electrosphere is quite general and will also be valid at the surface of strange-quark stars, should they exist.

astro-ph.GA↗

arXiv2010

Large-Scale Magnetic Fields, Dark Energy and QCD

Cosmological magnetic fields are being observed with ever increasing correlation lengths, possibly reaching the size of superclusters, therefore disfavouring the conventional picture of generation through primordial seeds later amplified by galaxy-bound dynamo mechanisms. In this paper we put forward a fundamentally different approach that links such large-scale magnetic fields to the cosmological vacuum energy. In our scenario the dark energy is due to the Veneziano ghost (which solves the $U(1)_A$ problem in QCD). The Veneziano ghost couples through the triangle anomaly to the electromagnetic field with a constant which is unambiguously fixed in the standard model. While this interaction does not produce any physical effects in Minkowski space, it triggers the generation of a magnetic field in an expanding universe at every epoch. The induced energy of the magnetic field is thus proportional to cosmological vacuum energy: $ρ_{EM}\simeq B^2 \simeq (\fracα{4π})^2 ρ_{DE}$, $ρ_{DE}$ hence acting as a source for the magnetic energy $ρ_{EM}$. The corresponding numerical estimate leads to a magnitude in the nG range. There are two unique and distinctive predictions of our proposal: an uninterrupted active generation of Hubble size correlated magnetic fields throughout the evolution of the universe; the presence of parity violation on the enormous scales $1/H$, which apparently has been already observed in CMB. These predictions are entirely rooted into the standard model of particle physics.

astro-ph.CO↗

arXiv2010

The cosmological constant from the QCD Veneziano ghost

We suggest that the solution to the cosmological vacuum energy puzzle is linked to the infrared sector of the effective theory of gravity interacting with standard model fields, with QCD fields specifically. We work in the framework of low energy quantum gravity as an effective field theory. In particular, we compute the vacuum energy in terms of QCD parameters and the Hubble constant $H$ such that the vacuum energy is $ε_{vac} \sim H \cdot m_q\la\bar{q}q\ra /m_{η'} \sim (3.6\cdot 10^{-3} \text{eV})^4$, which is amazingly close to the observed value today. The QCD ghost (responsible for the solution of the $U(1)_A$ problem) plays a crucial rôle in the computation of the vacuum energy, because the ghost's properties at very large but finite distances slightly deviate (as $\sim H / \Lqcd $) from their infinite volume Minkowski values. Another important prediction of this framework states that the vacuum energy owes its existence to the asymmetry of the cosmos. Indeed, this effect is a direct consequence of the embedding of our Universe on a non-trivial manifold such as a torus with (slightly) different linear sizes. Such a violation of cosmological isotropy is apparently indeed supported by WMAP, and will be confirmed (or ruled out) by future PLANCK data.

gr-qc↗

arXiv2010

The QCD nature of Dark Energy

The origin of the observed dark energy could be explained entirely within the standard model, with no new fields required. We show how the low-energy sector of the chiral QCD Lagrangian, once embedded in a non-trivial spacetime, gives rise to a cosmological vacuum energy density which can be can be presented entirely in terms of QCD parameters and the Hubble constant $H$ as $ρ_Λ\simeq H \cdot m_q\la\bar{q}q\ra /m_{η'} \sim (4.3\cdot 10^{-3} \text{eV})^4$. In this work we focus on the dynamics of the ghost fields that are essential ingredients of the aforementioned Lagrangian. In particular, we argue that the Veneziano ghost, being unphysical in the usual Minkowski QFT, becomes a physical degree of freedom if the universe is expanding. As an immediate consequence, all relevant effects are naturally very small as they are proportional to the rate of expansion $H/ \Lqcd \sim 10^{-41}$. The co-existence of these two drastically different scales ($\Lqcd \sim 100 $ MeV and $H \sim 10^{-33}$ eV) is a direct consequence of the auxiliary conditions on the physical Hilbert space that are necessary to keep the theory unitary. The exact cancellation taking place in Minkowski space due to this auxiliary condition is slightly violated when the system is upgraded to an expanding background. Nevertheless, this "tiny" effect is in fact the driving force accelerating the universe today. We also derive the time dependent equation of state $w(t)$ for the dark energy component which tracks the dynamics of the Veneziano ghost in a FLRW universe. Finally, we comment on how the same physical phenomena can be recovered in Witten's approach to the U(1) problem when the ghost degree of freedom is not even present in the system.

astro-ph.CO↗

arXiv2009

Cosmological constant, violation of cosmological isotropy and CMB

We suggest that the solution to the cosmological vacuum energy puzzle does not require any new field beyond the standard model, but rather can be explained as a result of the interaction of the infrared sector of the effective theory of gravity with standard model fields. The cosmological constant in this framework can be presented in terms of QCD parameters and the Hubble constant $H$ as follows, $ε_{vac} \sim H \cdot m_q\la\bar{q}q\ra /m_{η'} \sim (4.3\cdot 10^{-3} \text{eV})^4$, which is amazingly close to the observed value today. In this work we explain how this proposal can be tested by analyzing CMB data. In particular, knowing the value of the observed cosmological constant fixes univocally the smallest size of the spatially flat, constant time 3d hypersurface which, for instance in the case of an effective 1-torus, is predicted to be around 74 Gpc. We also comment on another important prediction of this framework which is a violation of cosmological isotropy. Such anisotropy is indeed apparently observed by WMAP, and will be confirmed (or ruled out) by future PLANCK data.

astro-ph.CO↗

arXiv2009

The cosmological constant from the ghost. A toy model

We suggest that the solution to the cosmological vacuum energy puzzle is linked to the infrared sector of the effective theory of gravity interacting with standard model fields. We propose a specific solvable two dimensional model where our proposal can be explicitly tested. We analyse the 2d Schwinger model on a 2-torus and in curved 2d space, mostly exploiting the properties of its topological susceptibility, its links with the non-trivial topology or deviations from spacetime flatness, and its relations to the real 4d world. The Kogut-Susskind ghost (which is a direct analogue of the Veneziano ghost in 4d) on a 2-torus and in curved 2d space plays a crucial role in the computation of the vacuum energy. The departure from Minkowski flatness, which is defined as the cosmological constant in our framework, is found to scale as 1/L, where L is the linear size of the torus. Therefore, in spite of the fact that the physical sector of 2d QED is represented by a single massive scalar particle, the deviation from Minkowski space is linear in L rather than exponentially suppressed as one could naively expect.

hep-th↗

arXiv2009

Deconfinement Phase Transition in Hot and Dense QCD at Large N

We conjecture that the confinement- deconfinement phase transition in QCD at large number of colors $N$ and $N_f\ll N$ at $T\neq 0$ and $μ\neq 0$ is triggered by the drastic change in $θ$ behavior. The conjecture is motivated by the holographic model of QCD where confinement -deconfinement phase transition indeed happens precisely at $T=T_c$ where $θ$ dependence experiences a sudden change in behavior. The conjecture is also supported by quantum field theory arguments when the instanton calculations (which trigger the $θ$ dependence) are under complete theoretical control for $T>T_c$, suddenly break down immediately below $T<T_c$ with sharp changes in the $θ$ dependence. Finally, the conjecture is supported by a number of numerical lattice results. We employ this conjecture to study confinement -deconfinement phase transition of hot and dense QCD in large $N$ limit by analyzing the $θ$ dependence. We estimate the critical values for $T_c$ and $μ_c$ where the phase transition happens by approaching the critical values from the hot and/or dense regions where the instanton calculations are under complete theoretical control. We also describe some defects of various codimensions within a holographic model of QCD by focusing on their role around the phase transition point.

hep-ph↗