arXiv subjects

Alexander Nikolaev

Publications and source records attributed to Alexander Nikolaev.

7 recordsLinked to original sources

arXiv2025

Jet Quenching in Holographic QCD as an Indicator of Phase Transitions in Anisotropic Regimes

In this paper, we employ the gauge/gravity duality to study jet quenching (JQ) phenomena in the quark-gluon plasma. For this purpose, we implement holographic QCD models constructed from an Einstein-Maxwell-dilaton gravity at finite temperature and finite chemical potential for light and heavy quarks. The models capture both the confinement and deconfinement phases of QCD and the first-order phase transitions. We calculate the JQ parameter in different models and compare them with the experimental data obtained in heavy-ions studies. In particular, we investigate how JQ, as a function of temperature $T$, chemical potential $\mu$, and magnetic field $c_B$, serves as a probe for identifying first-order phase transitions within the $(T,\mu,c_B)$ parameter space of holographic QCD. Particular attention is paid to the dependence of JQ on the parameter $\nu$, which characterizes longitudinal versus transverse anisotropy relative to the heavy-ion collision axis. By analyzing the dependence of the JQ parameters on these thermodynamic variables, we map critical regions associated with phase boundaries. We compare our findings to earlier studies of the running coupling constant's behavior within the gauge-gravity duality framework. This approach provides new insights into the interplay between non-perturbative dynamics and phase structure in strongly coupled systems.

hep-th↗

arXiv2025

Holographic QCD Running Coupling for Heavy Quarks in Strong Magnetic Field

We investigate the influence of a magnetic field on the running coupling constant for a heavy-quark model in a bottom-up holographic approach. To achieve this, we employ a magnetized Einstein-Maxwell-dilaton background that captures the essential features of heavy quark dynamics. Similar to the light-quark model, the running coupling $\alpha$ for heavy quarks decreases in the presence of a strong external magnetic field at fixed temperature and chemical potential. The key distinction between the light and heavy quark models lies in the locations of their respective phase transitions. However, near the 1st order phase transitions, the behavior of $\alpha$ is analogous for both cases: $\alpha$ exhibits jumps that depend on temperature, chemical potential, and magnetic field strength.

hep-th↗

arXiv2024

Holographic QCD Running Coupling for Light Quarks in Strong Magnetic Field

We consider running coupling constant in holographic model with external magnetic field supported by Einstein-dilaton-three-Maxwell action. We obtain a significant dependence of the running coupling constant $\alpha$ on chemical potential, temperature and magnetic field. We use the boundary condition that ensures the agreement with lattice calculations of string tension between quarks at zero chemical potential. The location of the 1st order phase transitions in $(\mu, T)$-plane does not depend on the dilaton boundary conditions. We observe that running coupling $\alpha$ decreases with increasing magnetic field for the fixed values of chemical potential and temperature. At the 1st order phase transitions the functions $\alpha$ undergo jumps depending on temperature, chemical potential and magnetic field.

hep-th↗

arXiv2024

Holographic RG flows in a 3d gauged supergravity at finite temperature

In this paper we consider finite-temperature holographic RG flows in $D=3$ $\mathcal{N}=(2,0)$ gauged truncated supergravity coupled to a sigma model with a hyperbolic target space. In the context of the holographic duality, fixed points (CFTs) at finite temperature are described by AdS black holes. We come from the gravity EOM to a 3d autonomous dynamical system, which critical points can be related to fixed points of dual field theories. Near-horizon black hole solutions correspond to infinite points of this system. We use Poincar\'e transformations to project the system on $\mathbf{R}^3$ into the 3d unit cylinder such that the infinite points are mapped onto the boundary of the cylinder. We explore numerically the space of solutions. We show that the exact RG flow at zero temperature is the separatrix for asymptotically AdS black hole solutions if the potential has one extremum, while for the potential with three extrema the separatrices are RG flows between AdS fixed points. We find near-horizon analytical solutions for asymptotically AdS black holes using the dynamical equations. We also present a method for constructing full analytical solutions.

hep-th↗

arXiv2024

Relaxed Clique Percolation and Disinformation-Resilient Domains for Social Commerce Networks

Must we trace and block all fake content in a social commerce network so that genuine users may enjoy fake-free information? Such efforts largely fail, because, as we get better at spam detection, spammers use the same advances for anti-detection. As a fundamentally new approach, we show that an online platform can aggregate and route user-generated content in a smart personalized way, which fosters and relies on "collective social responsibility". We introduce the notion of information aggregation domain, or simply, domain: composed for a given "central" node (user account), a domain is a connected set of nodes whose user-generated content is eligible to be used to meet the central node's information needs. Admitting malicious information sources - "bad citizen" nodes - into "good citizen" nodes' domains puts the good citizens at risk for disinformation attacks. We show how a platform can limit this risk by exploiting the social link structure between its nodes without the need to know which nodes are good or bad citizens. We introduce Relaxed Clique Percolation (RCP), a class of policies to compose personalized disinformation-resilient domains. Then, we define "RCP cores" and show how they can be used to efficiently compose resilient domains for all network nodes at once. Finally, we analyze the properties of RCP domains found in real-world social networks including Slashdot, Facebook, Flickr, and Yelp, to affirm that in practice, RCP domains turn out to be large and spatially diverse.

cs.SI↗

arXiv2020

Adversarial Balancing-based Representation Learning for Causal Effect Inference with Observational Data

Learning causal effects from observational data greatly benefits a variety of domains such as health care, education and sociology. For instance, one could estimate the impact of a new drug on specific individuals to assist the clinic plan and improve the survival rate. In this paper, we focus on studying the problem of estimating Conditional Average Treatment Effect (CATE) from observational data. The challenges for this problem are two-fold: on the one hand, we have to derive a causal estimator to estimate the causal quantity from observational data, where there exists confounding bias; on the other hand, we have to deal with the identification of CATE when the distribution of covariates in treatment and control groups are imbalanced. To overcome these challenges, we propose a neural network framework called Adversarial Balancing-based representation learning for Causal Effect Inference (ABCEI), based on the recent advances in representation learning. To ensure the identification of CATE, ABCEI uses adversarial learning to balance the distributions of covariates in treatment and control groups in the latent representation space, without any assumption on the form of the treatment selection/assignment function. In addition, during the representation learning and balancing process, highly predictive information from the original covariate space might be lost. ABCEI can tackle this information loss problem by preserving useful information for predicting causal effects under the regularization of a mutual information estimator. The experimental results show that ABCEI is robust against treatment selection bias, and matches/outperforms the state-of-the-art approaches. Our experiments show promising results on several datasets, representing different health care domains among others.

cs.LG↗

arXiv2019

Gluon propagators in QC$_2$D at high baryon density

We study the transverse and longitudinal gluon propagators in the Landau-gauge lattice QCD with gauge group $SU(2)$ at nonzero quark chemical potential and zero temperature. We show that both propagators demonstrate substantial dependence on the quark chemical potential. This observation contradicts to earlier findings by other groups.

hep-lat↗