## 1 Introduction
### Motivation  
Several studies have found that an increase in field-line resonances can lead to changes in cardiovascular function [18; 21; 23; 34]. Given the recent findings, that human HRV exhibits a much slower wave rhythm than had been previously identified, which can also synchronize to changes in the spectral power of field-line resonant frequencies, this study extends previous studies in several ways. Firstly, the previous studies used groups that located in one geographical area. Here we recruited groups located in five countries with a large geographical separation in order to determine if the HRV synchronization to the field-line resonances occurs globally, and determine if there are differing field-line resonant frequencies in different locations.  
Furthermore, one of the recent studies demonstrated that participant's psychological state and quality of social interactions between group members is related to the degree of HRV synchronization with the magnetic field activity and other participants in the group [11]. Another research study hypothesized that an individual in a state of physiological or HRV coherence is more likely to be coupled to and have a higher degree of synchronization with Earth's magnetic field [28]. In order to test this assumption, this study also inspected the potential effects of a heart-focused meditation technique called the Heart Lock-In (HLI), which has been shown to increase the coherence in one's heart rhythms as well as increase the synchronization of heart rhythms between participants in a group setting [35].  
A newly developed and validated methodology utilizing near-optimal chaotic attractor embedding techniques was used in order to enhance the assessment of physiological synchronization and identify individuals' response patterns [11]. Consequently, we were able to identify specific patterns of synchronization between HRV and local magnetic field activity, and assess potential effects of participants being in a state of HRV coherence on synchronization to each other and with the earth's magnetic field in diverse groups of people located in different countries around the planet.  
The main objective of this paper is to determine if the results reported in [11; 23] could be replicated on a global scale, and to determine if the participants' degree of synchronization with each other and local magnetic field could be increased by using a technique known to increase heart rhythm coherence.  
This paper is organized as follows. The overview and the details of HRV and local magnetic field data acquisition and filtering are presented in Sections 2.1-2.3 and 2.5. The steps as well as the observed effects of the used Heart Lock-In meditation technique are given in Section 2.4. The procedure used for the evaluation of synchronization between participants' HRV and local magnetic field is presented in Section 2.6. The main idea of this procedure is based on the fact that the data signal can be used to reconstruct the underlying chaotic dynamical system corresponding to the observed phenomena (for example, heart rate variability or local magnetic field spectral power, etc.). In order for such reconstruction to be meaningful and to preserve the properties of the underlying dynamical system, the optimal reconstruction parameters should be selected. The comparison of such optimal parameters corresponding to two data signals allows to assess the synchronization between these signals. Sections 2.7 and 2.8 overview the details of the analysis of synchronization between participants' HRV and Earth's magnetic field. The results of this analysis are given Section 3. The summary of the obtained results as well as possible limitations and suggestions for the future studies are presented in Sections 4 and 5.