arXiv subjects

Matti Jarvinen

Publications and source records attributed to Matti Jarvinen.

At least 37 records · Page 2Linked to original sources

arXiv2017

Holographic QCD in the Veneziano limit at finite Magnetic Field and Chemical Potential

We investigate the phase diagram of QCD-like gauge theories at strong coupling at finite magnetic field $B$, temperature $T$ and baryon chemical potential $μ$ using the improved holographic QCD model including the full backreaction of the quarks in the plasma. In addition to the phase diagram we study the behavior of the quark condensate as a function of $T$, $B$ and $μ$ and discuss the fate of (inverse) magnetic catalysis at finite $μ$. In particular we observe that inverse magnetic catalysis exists only for small values of the baryon chemical potential. The speed of sound in this holographic quark-gluon plasma exhibits interesting dependence on the thermodynamic parameters.

hep-th↗

arXiv2017

Holographic sliding stripes

Holographic models provide unique laboratories to investigate non-linear physics of transport in inhomogeneous systems. We provide a detailed account of both DC and AC conductivities in a defect CFT with spontaneous stripe order. The spatial symmetry is broken at large chemical potential and the resulting ground state is a combination of a spin and charge density wave. An infinitesimal applied electric field across the stripes will cause the stripes to slide over the underlying density of smeared impurities, a phenomenon which can be associated with the Goldstone mode for the spontaneously broken translation symmetry. We show that the presence of a spatially modulated background magnetization current thwarts the expression of some DC conductivities in terms of horizon data.

hep-th↗

arXiv2016

Theta angle in holographic QCD

V-QCD is a class of effective holographic models for QCD which fully includes the backreaction of quarks to gluon dynamics. The physics of the theta-angle and the axial anomaly can be consistently included in these models. We analyze their phase diagrams over ranges of values of the quark mass, N_f/N_c, and theta, computing observables such as the topological susceptibility and the meson masses. At small quark mass, where effective chiral Lagrangians are reliable, they agree with the predictions of V-QCD.

hep-ph↗

arXiv2015

Massive holographic QCD in the Veneziano limit

QCD at finite, flavor independent quark mass is analyzed by using bottom-up holography in the Veneziano limit, where the backreaction of quarks to the gluon dynamics is fully included. The dependence on the quark mass of observables such as the bound state masses, the chiral condensate, the S-parameter, and the critical temperatures is studied. Many of the results are argued to be universal, i.e., independent of the details of the holographic model, and compared to explicit computations in the V-QCD models. The effect of adding four-fermion operators in QCD is also discussed.

hep-ph↗

arXiv2015

Recent progress in backreacted bottom-up holographic QCD

Recent progress in constructing holographic models for QCD is discussed, concentrating on the bottom-up models which implement holographically the renormalization group flow of QCD. The dynamics of gluons can be modeled by using a string-inspired model termed improved holographic QCD, and flavor can be added by introducing space filling branes in this model. The flavor fully backreacts to the glue in the Veneziano limit, giving rise to a class of models which are called V-QCD. The phase diagrams and spectra of V-QCD are in good agreement with results for QCD obtained by other methods.

hep-ph↗

arXiv2015

Holography and the conformal window in the Veneziano limit

We discuss holographic QCD in the Veneziano limit (the V-QCD models), concentrating on phenomena near the "conformal" phase transition taking place at a critical value of the ratio x = N_f/N_c. In particular, we review the results for the S-parameter, the technidilaton, and the masses of the mesons.

hep-ph↗

arXiv2015

Late time behavior of non-conformal plasmas

We determine analytically the dependence of the approach to thermal equilibrium of strongly coupled plasmas on the breaking of scale invariance. The theories we consider are the holographic duals to Einstein gravity coupled to a scalar with an exponential potential. The coefficient in the exponent, $X$, is the parameter that controls the deviation from the conformally invariant case. For these models we obtain analytic solutions for the plasma expansion in the late-time limit, under the assumption of boost-invariance, and we determine the scaling behaviour of the energy density, pressure, and temperature as a function of time. We find that the temperature decays as a function of proper time as $T\sim τ^{-s/4}$ with $s$ determined in terms of the non-conformality parameter $X$ as $s=4(1-4X^2)/3$. This agrees with the result of Janik and Peschanski, $s=4/3$, for the conformal plasmas and generalizes it to non-conformal plasmas with $X\neq 0$. We also consider more realistic potentials where the exponential is supplemented by power-law terms. Even though in this case we cannot have exact solutions, we are able under certain assumptions to determine the scaling of the energy, that receives logarithmic corrections.

hep-th↗

arXiv2014

Gravity dual of spin and charge density waves

At high enough charge density, the homogeneous state of the D3-D7' model is unstable to fluctuations at nonzero momentum. We investigate the end point of this instability, finding a spatially modulated ground state, which is a charge and spin density wave. We analyze the phase structure of the model as a function of chemical potential and magnetic field and find the phase transition from the homogeneous state to be first order, with a second-order critical point at zero magnetic field.

hep-th↗

arXiv2014

Constraints on Majorana Dark Matter from a Fourth Lepton Family

We study the possibility of dark matter in the form of heavy neutrinos from a fourth lepton family with helicity suppressed couplings such that dark matter is produced thermally via annihilations in the early Universe. We present all possible constraints for this scenario coming from LHC and collider physics, underground direct detectors, neutrino telescopes, and indirect astrophysical searches. Although we embed the WIMP candidate within a model of composite dynamics, the majority of our results are model independent and applicable to all models where heavy neutrinos with suppressed couplings account for the dark matter abundance.

hep-ph↗

arXiv2013

Moduli space of supersymmetric QCD in the Veneziano limit

We study the moduli space of 4d N=1 supersymmetric QCD in the Veneziano limit using Hilbert series. In this limit, the numbers of colours and flavours are taken to be large with their ratio fixed. It is shown that the Hilbert series, which is a partition function of an ensemble of gauge invariant quantities parametrising the moduli space, can also be realised as a partition function of a system of interacting Coulomb gas in two dimensions. In the electrostatic equilibrium, exact and asymptotic analyses reveal that such a system exhibits two possible phases. Physical quantities, such as charge densities, free energies, and Hilbert series, associated with each phase, are computed explicitly and discussed in detail. We then demonstrate the existence of the third order phase transition in this system.

hep-th↗

arXiv2013

The discontinuities of conformal transitions and mass spectra of V-QCD

Zero temperature spectra of mesons and glueballs are analyzed in a class of holographic bottom-up models for QCD in the Veneziano limit, N_c -> infinity, N_f -> infinity, with x = N_f/N_c fixed (V-QCD). The backreaction of flavor on color is fully included. It is found that spectra are discrete and gapped (modulo the pions) in the QCD regime, for x below the critical value x_c where the conformal transition takes place. The masses uniformly converge to zero in the walking region x -> x_c^- due to Miransky scaling. All the ratios of masses asymptote to non-zero constants as x -> x_c^- and therefore there is no "dilaton" in the spectrum. The S-parameter is computed and found to be of O(1) in units of N_f N_c in the walking regime, while it is always an increasing function of x. This indicates the presence of a subtle discontinuity of correlation functions across the conformal transition at x = x_c.

hep-ph↗

arXiv2013

The spectrum of (h)QCD in the Veneziano limit

In this note we report on the analysis of the zero temperature spectra of glueballs and mesons for holographic QCD in the Veneziano limit. We work within a holographic bottom-up model named V-QCD which takes into account the full backreaction of the flavor degrees of freedom. By studying the fluctuations of this model we compute spectra of mesons and glueballs as a function of x=N_f/N_c. The spectra are discrete and gapped (modulo the pions) in the QCD regime, where x is below the critical value x_c at which the conformal transition takes place. The masses uniformly converge to zero in the walking region x -> x_c following Miransky scaling. Moreover, all the ratios of masses asymptote to finite constants as x -> x_c. Therefore there is no "dilaton" in the spectrum. Finally, we compute the S-parameter, which is found to be of O(1) in the walking regime.

hep-ph↗

arXiv2013

Towards a Born term for hadrons

We study bound states of abelian gauge theory in D=1+1 dimensions using an equal-time, Poincare-covariant framework. The normalization of the linear confining potential is determined by a boundary condition in the solution of Gauss' law for the instantaneous A^0 field. As in the case of the Dirac equation, the norm of the relativistic fermion-antifermion (f\bar{f}) wave functions gives inclusive particle densities. However, while the Dirac spectrum is known to be continuous, we find that regular f\bar{f} solutions exist only for discrete bound state masses. The f\bar{f} wave functions are consistent with the parton picture when the kinetic energy of the fermions is large compared to the binding potential. We verify that the electromagnetic form factors of the bound states are gauge invariant and calculate the parton distributions from the transition form factors in the Bjorken limit. For relativistic states we find a large sea contribution at low Bjorken x. Since the potential is independent of the gauge coupling the bound states may serve as "Born terms" in a perturbative expansion, in analogy to the usual plane wave in and out states.

hep-ph↗

arXiv2013

Fluctuations and instabilities of a holographic metal

We analyze the quasinormal modes of the D2-D8' model of 2+1-dimensional, strongly-coupled, charged fermions in a background magnetic field and at nonzero density. The model is known to include a quantum Hall phase with integer filling fraction. As expected, we find a hydrodynamical diffusion mode at small momentum and the nonzero-temperature holographic zero sound, which becomes massive above a critical magnetic field. We confirm the previously-known thermodynamic instability. In addition, we discover an instability at low temperature, large mass, and in a charge density and magnetic field range near the quantum Hall phase to an inhomogeneous striped phase.

hep-th↗

arXiv2012

New results for the SQCD Hilbert series

We derive new explicit results for the Hilbert series of N=1 supersymmetric QCD with U(N_c) and SU(N_c) color symmetry. We use two methods which have previously been applied to similar computational problems in the analysis of decay of unstable D-branes: expansions using Schur polynomials, and the log-gas approach related to random matrix theory.

hep-th↗

arXiv2012

V-QCD: Spectra, the dilaton and the S-parameter

Zero temperature spectra of mesons and glueballs are analyzed in a class of holographic bottom-up models for QCD (named V-QCD), as a function of x = N_f/N_c with the full back-reaction included. It is found that spectra are discrete and gapped (modulo the pions) in the QCD regime, for x below the critical value x_c where the conformal transition takes place. The masses uniformly converge to zero in the walking region x -> x_c due to Miransky scaling. The ratio of masses all asymptote to non-zero constants as x -> x_c and therefore there is no "dilaton" in the spectrum. The S-parameter is computed and found to be of O(1) in the walking regime.

hep-ph↗

arXiv2012

Boosting equal time bound states

We present an explicit and exact boost of a relativistic bound state defined at equal time of the constituents in the Born approximation (lowest order in hbar). To this end, we construct the Poincaré generators of QED and QCD in D=1+1 dimensions, using Gauss' law to express A^0 in terms of the fermion fields in A^1=0 gauge. We determine the fermion-antifermion bound states in the Born approximation as eigenstates of the time and space translation generators P^0 and P^1. The boost operator is combined with a gauge transformation so as to maintain the gauge condition A^1=0 in the new frame. We verify that the boosted state remains an eigenstate of P^0 and P^1 with appropriately transformed eigenvalues and determine the transformation law of the equal-time, relativistic wave function. The shape of the wave function is independent of the CM momentum when expressed in terms of a variable, which is quadratically related to the distance x between the fermions. As a consequence, the Lorentz contraction of the wave function is proportional to 1/(E-V(x)) and thus depends on x via the linear potential V(x).

hep-ph↗

arXiv2012

Fluctuations of a holographic quantum Hall fluid

We analyze the neutral spectrum of the holographic quantum Hall fluid described by the D2-D8' model. As expected for a quantum Hall state, we find the system to be stable and gapped and that, at least over much of the parameter space, the lowest excitation mode is a magneto-roton. In addition, we find magneto-rotons in higher modes as well. We show that these magneto-rotons are direct consequences of level crossings between vector and scalar modes.

hep-th↗