arXiv subjects

Barak Bringoltz

Publications and source records attributed to Barak Bringoltz.

At least 19 recordsLinked to original sources

arXiv2025

Learning the Language of NVMe Streams for Ransomware Detection

We apply language modeling techniques to detect ransomware activity in NVMe command sequences. We design and train two types of transformer-based models: the Command-Level Transformer (CLT) performs in-context token classification to determine whether individual commands are initiated by ransomware, and the Patch-Level Transformer (PLT) predicts the volume of data accessed by ransomware within a patch of commands. We present both model designs and the corresponding tokenization and embedding schemes and show that they improve over state-of-the-art tabular methods by up to 24% in missed-detection rate, 66% in data loss prevention, and 84% in identifying data accessed by ransomware.

cs.LG↗

arXiv2012

Large-N reduction with adjoint Wilson fermions

We analyze the large-N behavior of SU(N) lattice gauge theories with adjoint fermions by studying volume-reduced models, as pioneered by Eguchi and Kawai. We perform simulations on a single-site lattice for Nf = 1 and Nf = 2 Wilson Dirac fermions with values of N up to 53. We show for both values of Nf that in the large-N limit there is a finite region, containing both light and heavy fermions, of unbroken center symmetry where the theory exhibits volume independence. Using large-N reduction we attempt to calculate physical quantities such as the string tension and meson masses.

hep-lat↗

arXiv2012

Large-N reduction in QCD with two adjoint Dirac fermions

We use lattice simulations to study the single-site version of SU(N) lattice gauge theory with two flavors of Wilson-Dirac fermions in the adjoint representation, a theory whose large volume correspondent is expected to be conformal or nearly conformal. Working with N as large as 53, we map out the phase diagram in the plane of bare `t Hooft coupling, g^2 N, and of the lattice quark mass, a*m, and look for the region where the Z_N^4 center symmetry of the theory is intact. In this region one expects the large-N equivalence of the single site and infinite volume theories to be valid. As for the N_f=1 case (see Phys. Rev. D80: 065031), we find that the center-symmetric region is large and includes both light fermion masses and masses at the cutoff scale. We study the N-dependence of the width of this region and find strong evidence that it remains of finite width as N goes to infinity. Simulating with couplings as small as g^2 N = 0.005, we find that the width shrinks slowly with decreasing g^2 N, at a rate consistent with analytic arguments. Within the center-symmetric region our results for the phase structure, when extrapolated to infinite N, apply also for the large volume theory, which is minimal walking technicolor with N=infinity. We find a first-order transition as a function of a*m for all values of b, which we argue favors that the theory is confining in the infrared. Finally, we measure the eigenvalue densities of the Wilson-Dirac operator and its hermitian version, and use large Wilson loops to study the utility of reduction for extracting physical observables.

hep-lat↗

arXiv2011

Large-N reduction with two adjoint Dirac fermions

We study the single site SU(N) lattice gauge theory with N_f=2 adjoint Wilson fermions for values of N up to 53. We determine the phase diagram of the theory as a function of the hopping parameter kappa and the inverse 't Hooft coupling b, searching for the region in which the Z_N^4 center symmetry is unbroken. In this region the theory is equivalent to the infinite volume theory when N goes to infinity. We find a region of values of kappa on both sides of kappa_c for which the symmetry is unbroken, including both light physical quarks and masses ~O(1/a). This is surrounded by a region with a complicated sequence of partially broken phases. We calculate Wilson loop expectation values and find that using N <= 53 it is possible to extract the heavy-quark potential at small distances (1-3 links) but not at longer distances. For this, larger values of N, or lattices with more sites, are needed.

hep-lat↗

arXiv2011

Closed flux tubes and their string description in D=2+1 SU(N) gauge theories

We carry out lattice calculations of the spectrum of confining flux tubes that wind around a spatial torus of variable length l, in 2+1 dimensions. We compare the energies of the lowest c.30 states to the free string Nambu-Goto model and to recent results on the universal properties of effective string actions. Our most useful calculations are in SU(6) at a small lattice spacing, which we check is very close to the large-N continuum limit. We find that the energies, En(l), are remarkably close to the predictions of the free string Nambu-Goto model, even well below the critical length at which the expansion of the Nambu-Goto energy in powers of 1/l diverges and the series needs to be resummed. Our analysis of the ground state supports the universality of the O(1/l) and the O(1/l^3) corrections to l.sigma, and we find that the deviations from Nambu-Goto at small l prefer a leading correction that is O(1/l^7), consistent with theoretical expectations. We find that the low-lying states that contain a single phonon excitation are also consistent with the leading O(1/l^7) correction dominating down to the smallest values of l. By contrast our analysis of the other light excited states clearly shows that for these states the corrections at smaller l resum to a much smaller effective power. Finally, and in contrast to our recent calculations in D=3+1, we find no evidence for the presence of any non-stringy states that could indicate the excitation of massive flux tube modes.

hep-lat↗

arXiv2010

Closed flux tubes and their string description in D=3+1 SU(N) gauge theories

We calculate the energy spectrum of a confining flux tube that is closed around a spatial torus, as a function of its length l. We do so for various SU(N) gauge theories in 3+1 dimensions, and for various values of spin, parity and longitudinal momentum. We are able to present usefully accurate results for about 20 of the lightest such states, for a range of l that begins close to the (finite volume) deconfining phase transition, and extends up to l.sqrt(K)~6 (where K is the string tension). We find that most of these low-lying states are well described by the spectrum of the Nambu-Goto free string theory in flat space-time. Remarkably, this is so not only at the larger values of l, where the gap between the ground state energy and the low-lying excitations becomes small compared to the mass gap, but also down to much shorter lengths where these excitation energies become large compared to sqrt(K), the flux-tube no longer `looks' anything like a thin string, and an expansion of the effective string action in powers of 1/l no longer converges. All this is for flux in the fundamental representation. We also calculate the k=2 (anti)symmetric ground states and these show larger corrections at small l. So far all this closely resembles our earlier findings in 2+1 dimensions. However, and in contrast to the situation in D=2+1, we also find that there are some states, with J,P=0,- quantum numbers, that show large deviations from the Nambu-Goto spectrum. We investigate the possibility that (some of) these states may encode the massive modes associated with the internal structure of the flux tube, and we discuss how the precocious free string behaviour of most states constrains the effective string action, on which much interesting theoretical progress has recently been made.

hep-lat↗

arXiv2010

Large-N spacetime reduction and the sign and silver-blaze problems of dense QCD

We study the spacetime-reduced (Eguchi-Kawai) version of large-N QCD with nonzero chemical potential. We explore a method to suppress the sign fluctuations of the Dirac determinant in the hadronic phase; the method employs a re-summation of gauge configurations that are related to each other by center transformations. We numerically test this method in two dimensions, and find that it successfully solves the silver-blaze problem. We analyze the system further, and measure its free energy F, the average phase theta of its Dirac determinant, and its chiral condensate . We show that F and are independent of mu in the hadronic phase but that, as chiral perturbation theory predicts, the quenched chiral condensate drops from its mu=0 value when mu~(pion mass)/2. Finally, we find that the distribution of theta qualitatively agrees with further, more recent, predictions from chiral perturbation theory.

hep-lat↗

arXiv2010

Partial breakdown of center symmetry in large-N QCD with adjoint Wilson fermions

We study the one-loop potential of large-N QCD with adjoint Dirac fermions. Space-time is a discretization of R^3 x S^1 where the compact direction consists of a single lattice site. We use Wilson fermions with different values of the quark mass m and set the lattice spacings in the compact and non-compact directions to be a_t and a_s respectively. Extending the results of JHEP 0906:091,2009, we prove that if the ratio xi = a_s/a_t obeys 0 > 1, while for large masses K ~ O(1). Despite certain UV sensitivities of the lattice one-loop potential, this phase structure is similar to the one obtained in the continuum works of Kovtun-Unsal-Yaffe, Myers-Ogilvie, and Hollowood-Myers. We explain the physical origin of the cascade of transitions and its relation to the embedding of space-time into color space.

hep-lat↗

arXiv2009

The spectrum of closed loops of fundamental flux in D = 3+1 SU(N) gauge theories

We study the spectrum of closed flux tubes in four dimensional SU(N) gauge theories. We do so by calculating the energies of the low lying states with the variational technique (whose basis consists of about ~700 operators). We study states of different values of angular momentum, transversal parity, longitudinal parity, and longitudinal momentum, and compare the results with effective string theories (ESTs) such as the Nambu-Goto (NG) model. Most of our states agree very well with the Nambu-Goto predictions and since most of our flux-tubes' lengths are outside the radius of convergence of the ESTs, then for some states it is only the NG that predicts the spectrum well. This strongly suggests that the ESTs can be re-summed. Nonetheless, there are a few states (all with negative parity and in the same representation of the lattice rotation group) that exhibit large deviations from the NG predictions; these deviations might provide clues to the nature of the effective string theory describing the large-N QCD string.

hep-lat↗

arXiv2009

Non-perturbative volume-reduction of large-N QCD with adjoint fermions

We use nonperturbative lattice techniques to study the volume-reduced "Eguchi-Kawai" version of four-dimensional large-N QCD with a single adjoint Dirac fermion. We explore the phase diagram of this single-site theory in the space of quark mass and gauge coupling using Wilson fermions for a number of colors in the range 8 <= N <= 15. Our evidence suggests that these values of N are large enough to determine the nature of the phase diagram for N-->oo. We identify the region in the parameter space where the (Z_N)^4 center-symmetry is intact. According to previous theoretical work using the orbifolding paradigm, and assuming that translation invariance is not spontaneously broken in the infinite-volume theory, in this region volume reduction holds: the single-site and infinite-volume theories become equivalent when N-->oo. We find strong evidence that this region includes both light and heavy quarks (with masses that are at the cutoff scale), and our results are consistent with this region extending towards the continuum limit. We also compare the action density and the eigenvalue density of the overlap Dirac operator in the fundamental representation with those obtained in large-N pure-gauge theory.

hep-lat↗

arXiv2009

Volume independence of large-N QCD with adjoint fermions

It has been proposed that four-dimensional QCD with fermions in the adjoint representation exhibits volume-independence in the large-N limit. If correct, this would mean that results for physical quantities could be obtained from the single-site version of the model. A necessary condition for volume-independence is that the (Z_N)^4 center-symmetry of the single-site theory is unbroken. We explore the phase diagram of the theory with a single Dirac fermion using Wilson fermions for a number of colors in the range N=8-15, and identify the region in the parameter space of quark mass and gauge coupling where the symmetry appears to be unbroken. Our evidence suggests that this region includes both light and heavy quarks, and our results are consistent with this region extending to the continuum limit.

hep-lat↗

arXiv2009

Solving two-dimensional large-N QCD with a nonzero density of baryons and arbitrary quark mass

We solve two-dimensional large-N QCD in the presence of a nonzero baryon number B, and for arbitrary quark mass m and volume L. We fully treat the dynamics of the gluonic zero modes and check how this affects results from previous studies of the B=0 and B=1 systems. For a finite density of baryons, and for any m>0, we find that the ground state contains a baryon crystal with expectation values for psi-bar gamma_mu psi that have a helix-like spatial structure. We study how these evolve with B and see that the volume integral of psi-bar psi strongly changes with the baryon density. We compare this emerging crystal structure with the sine-Gordon crystal, which is expected to be a good approximation for light quarks, and find that it is a very good approximation for surprisingly heavy quarks. We also calculate the way the ground state energy E changes as a function of the baryon number B, and find that for sufficiently large densities the function E(B) is well described by the equation of state for free massless quarks, thus suggesting a quark-Hadron continuity. From dE(B)/dB we calculate the quark chemical potential mu as a function of B and see that the baryons repel each other. The way mu depends on B also allows us to translate our findings to the grand-canonical ensemble. The resulting phase structure along the mu-axis contains a phase transition that occurs at a value of mu equal to the baryon mass divided in N, and that separates a mu-independent phase with intact translation symmetry from a mu-dependent phase with spontaneously broken translation symmetry. Finally, our calculations confirm the presence of a partial large-N Eguchi-Kawai volume independence, as described in Phys.Rev.D79:105021, that arises only if one treats the gluonic zero modes correctly.

hep-lat↗

arXiv2009

Volume dependence of two-dimensional large-N QCD with a nonzero density of baryons

We take a first step towards the solution of QCD in 1+1 dimensions at nonzero density. We regularize the theory in the UV by using a lattice and in the IR by putting the theory in a box of spatial size L. After fixing to axial gauge we use the coherent states approach to obtain the large-N classical Hamiltonian H that describes color neutral quark-antiquark pairs interacting with spatial Polyakov loops in the background of baryons. Minimizing H we get a regularized form of the `t Hooft equation that depends on the expectation values of the Polyakov loops. Analyzing the L-dependence of this equation we show how volume independence, a la Eguchi and Kawai, emerges in the large-N limit, and how it depends on the expectation values of the Polyakov loops. We describe how this independence relies on the realization of translation symmetry, in particular when the ground state contains a baryon crystal. Finally, we remark on the implications of our results on studying baryon density in large-N QCD within single-site lattice theories, and on some general lessons concerning the way four-dimensional large-N QCD behaves in the presence of baryons.

hep-lat↗

arXiv2009

Large-N volume reduction of lattice QCD with adjoint Wilson fermions at weak-coupling

We study the large-N volume reduction of QCD with adjoint quarks regularized on the lattice. Specifically, we use Wilson fermions, and while our d-dimensional lattice has (d-1) infinite dimensions, the remaining direction is reduced to a point. We perform a weak-coupling one-loop calculation of the free energy as a function of the holonomy in the reduced direction, and map the regimes in the bare lattice parameter space where the holonomy averages to zero and a Z_N-center symmetric configuration is the ground state. For d=4 and N_f=1/2,1 and 2 Dirac flavors we see that the center symmetry is intact in a generous regime of the phase diagram that includes the chiral point. Thus we see that large-N volume independence of lattice QCD with adjoint Wilson quarks works at weak coupling. Interestingly, we find that this is true even if the quark mass is quite large, and this opens a path to study the volume reduced large-N pure gauge theory. Finally, we analyze in detail the UV sensitivity of the one-loop potential and show that treating the reduced theory as a (d-1)-dimensional effective field theory requires the introduction of certain relevant operators that are a subset of those suggested by Unsal and Yaffe to stabilize the center symmetry. This means that different regularizations of the volume-reduced theory can be compared only if one includes these terms in the action.

hep-lat↗

arXiv2009

On the spectrum of closed k=2 flux tubes in D=2+1 SU(N) gauge theories

We calculate the energy spectrum of a k=2 flux tube that is closed around a spatial torus, as a function of its length l. We do so for SU(4) and SU(5) gauge theories in 2 space dimensions. We find that to a very good approximation the eigenstates belong to the irreducible representations of the SU(N) group rather than just to its center, Z_N. We obtain convincing evidence that the low-lying states are, for l not too small, very close to those of the Nambu-Goto free string theory (in flat space-time). The correction terms appear to be typically of O(1) in appropriate units, much as one would expect if the bosonic string model were an effective string theory for the dynamics of these flux tubes. This is in marked contrast to the case of fundamental flux tubes where such corrections have been found to be unnaturally small. Moreover we find that these corrections appear to be particularly small when the `phonons' along the string have the same momentum, and large when their momentum is opposite. This provides information about the detailed nature of the interactions in the effective string theory. We have searched for, but not found, extra states that would arise from the excitation of the massive modes presumably associated with the non-trivial structure of the flux tube.

hep-lat↗

arXiv2008

Breakdown of large-N reduction in the quenched Eguchi-Kawai model

We study the validity of the large-N equivalence between four-dimensional SU(N) lattice gauge theory and its momentum quenched version -- the Quenched Eguchi-Kawai (QEK) model. We have found strong evidence that this equivalence does not hold in the weak-coupling regime (and thus in the continuum limit). This is based on weak-coupling analytic arguments and Monto-Carlo simulations at intermediate couplings with 20 <= N <= 200. Since detailed expositions of our arguments, methods and results have already appeared in Phys. Rev. D78:034507 (2008) and Phys. Rev. D78:074503 (2008), we attempt here to give a more intuitive explanation of our results. The breakdown of reduction that we find is due to a dynamically generated correlation between different Euclidean components of the gauge fields.

hep-lat↗

arXiv2008

Applying the Wang-Landau Algorithm to Lattice Gauge Theory

We implement the Wang-Landau algorithm in the context of SU(N) lattice gauge theories. We study the quenched, reduced version of the lattice theory and calculate its density of states for N=20,30,40,50. We introduce a variant of the original algorithm in which the weight function used in the update does not asymptote to a fixed function, but rather continues to have small fluctuations which enhance tunneling. We formulate a method to evaluate the errors in the density of states, and use the result to calculate the dependence of the average action density and the specific heat on the `t Hooft coupling lambda. This allows us to locate the coupling lambda_t at which a strongly first order transition occurs in the system. For N=20 and 30 we compare our results to those obtained using Ferrenberg-Swendsen multi-histogram reweighting and find agreement with errors of 0.2 % or less. Extrapolating our results to N=oo we find 1/lambda_t = 0.3148(2). We remark on the significance of this result for the validity of quenched large-$N$ reduction of SU(N) lattice gauge theories.

hep-lat↗

arXiv2008

Spectrum of closed k-strings in D=2+1

We calculate the excitation spectrumof closed k-strings in 2+1 dimensional SU(N) gauge theories for N = 4, 5 and k = 2. Our results demonstrate that the low-lying spectrum of the k = 2 string falls into sectors that belong to nearly pure antisymmetric and symmetric representations, showing that k-strings know not only about the centre of the group, but also about the full group. We also observe that the lightest states in each irreducible representation are consistent with what one would expect from an effective string theory that belongs to the same bosonic universality class (Nambu-Goto) as the fundamental string. We find that the corrections compared to the free string theory are of O(1), in striking contrast to the very small correction observed for the fundamental string. We also observe unbound w = 2 states.

hep-lat↗