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2001, Journal of High Energy Physics
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13 pages
1 file
We study soliton solutions in scalar field theory with a variety of unbounded potentials. A subset of these potentials have Gaussian lump solutions and their fluctuation spectrum is governed by the harmonic oscillator problem. These lumps are unstable with one tachyonic mode. Soliton solutions in several other classes of potentials are stable and are of kink type. The problem of the stability of these solutions is related to a supersymmetric quantum mechanics problem. The fluctuation spectrum is not equispaced and does not contain any tachyonic mode. The lowest energy mode is the massless Goldstone mode which restores broken translation invariance.
Physics Letters B, 2001
We study soliton solutions in supersymmetric scalar field theory with a class of potentials. We study both bosonic and fermionic zero-modes around the soliton solution. We study two possible couplings of gauge fields to these models. While the Born-Infeld like coupling has one normalizable mode (the zero mode), the other kind of coupling has no normalizable modes. We show that quantum mechanical problem which determines the spectrum of fluctuation modes of the scalar, fermion and the gauge field is identical. We also show that only the lowest lying mode, i.e., the zero mode, is normalizable and the rest of the spectrum is continuous. *
Symmetry
This paper presents our study of the presence of the unstable critical point in spontaneous symmetry breaking (SSB) in the framework of Ginzburg–Landau (G-L) free energy. Through a 3D Ising spin lattice simulation, we found a zone of hysteresis where the unstable critical point continued to exist, despite the system having entered the broken symmetry phase. Within the hysteresis zone, the presence of the kink–antikink SSB solitons expands and, therefore, these can be observed. In scalar field theories, such as Higgs fields, the mass of this soliton inside the hysteresis zone could behave as a tachyon mass, namely as an imaginary quantity. Due to the fact that groups Ζ(2) and SU(2) belong to the same universality class, one expects that, in future experiments of ultra-relativistic nuclear collisions, in addition to the expected bosons condensations, structures of tachyon fields could appear.
Physical Review D, 2001
We discuss the tachyon condensation in a single unstable D-brane in the framework of boundary state formulation. The boundary state in the background of the tachyon condensation and the NS B-field is explicitly constructed. We show in both commutative theory and noncommutative theory that the unstable D-branes behaves like an extended object and eventually reduces to the lower dimensional D-branes as the system approaches the infrared fixed point. We clarify the relationship between the commutative field theoretical description of the tachyon condensation and the noncommutative one.
Journal of High Energy Physics, 2009
Recently, Hellerman and Schnabl considered the dynamics of unstable D-branes in the background of a linear dilaton. Remarkably, they were able to construct light-like tachyon solutions which interpolate smoothly between the perturbative and nonperturbative vacua, without undergoing the wild oscillations that plague time-like solutions. In their analysis, however, the full structure of the initial value problem for the nonlocal dynamical equations was not considered. In this paper, therefore, we reexamine the nonlinear dynamics of lightlike tachyon condensation using a combination of numerical and analytical techniques. We find that for the p-adic string the monotonic behaviour obtained previously relied on a special choice of initial conditions near the unstable maximum. For generic initial conditions the wild oscillations come back to haunt us. Interestingly, we find an "island of stability" in initial condition space that leads to sensible evolution at late times. For the string field theory case, on the other hand, we find that the evolution is completely stable for generic choices of initial data. This provides an explicit example of a string theoretic system that admits infinitely many initial data but is nevertheless nonperturbatively stable. Qualitatively similar dynamics are obtained in nonlocal cosmologies where the Hubble damping plays a role very analogous to the dilaton gradient.
Journal- Korean Physical Society
We consider condensation of localized closed string tachyons by examining the recent proposal of Harvey, Kutasov, Martinec, and Moore. We first observe that the g cl defined by HKMM does not reflect the space-time supersymmetry when the model has the SUSY. Especially for C 2 /Z N models, g cl defined by them is highly peaked along the supersymmetric points in the space of orbifolds, which is unsatisfactory property of the c-function of the RG-flow. We give the modified definition of the g cl in type II cases such that it has a valley along the supersymmetric points in the orbifold moduli space. New definition predicts that the processes suggested by Adams, Polchinski and Silverstein and was argued to be forbidden by HKMM are in fact allowed.
Journal of High Energy Physics, 2013
The stabilisation of the dilaton and volume in tree-level flux compactifications leads to model independent and thus very powerful existence and stability criteria for dS solutions. In this paper we show that the sizes of cycles wrapped by orientifold planes are scalars whose scalings in the potential are not entirely model independent, but enough to entail strong stability constraints. For all known dS solutions arising from massive IIA supergravity flux compactifications on SU(3)-structure manifolds the tachyons are exactly within the subspace spanned by the dilaton, the total volume and the volumes of the orientifold cycles. We illustrate this in detail for the well-studied case of the O6 plane compactification on SU(2) × SU(2)/Z 2 × Z 2. For that example we uncover another novel structure in the tachyon spectrum: the dS solutions have a singular, but supersymmetric, Minkowski limit, in which the tachyon exactly aligns with the sgoldstino.
… and Quantum Gravity, 2010
Scripta Cypria III Pyrgos/Mavroraki Copper Metallurgy I, 2024
Cyprus' copper wealth and high-quality minerals led to its identification as the Roman term cuprum (Kypros). However, evidence of copper processing is scarce before the Chalcolithic- Early Bronze age, therefore, the documentation presented in Scripta Cypria III sheds new light on the beginning of Cypriot metallurgy, which was a fundamental element in the evolution of maritime trade on the island. Other contemporary metallurgical sites in the Mediterranean, including Cyprus, are equally rich in copper but do not have the level of productive continuity of Pyrgos/Mavroraki, as according to the 14C the Pre-Ceramic Neolithic site continued to be inhabited until the end of the Middle Bronze age, when it was destroyed by an earthquake. The materials that identify Pyrgos/Mavroraki as a copper worker community represent all the production phases, from copper extraction to the finishing of the artefacts, in a 4000-year time span of technology evolution. Alongside the few copper objects that survived to the earthquake, complete processing plants, infrastructure, stone tools, slags and processing waste of various kinds have been found in different occupancy levels that were not continuously used in metallurgy. Alongside the working points, the fragments of crucibles and moulds, nozzles, bellows supports, and a vast lithic apparatus, including shaped anvils and mining tools for extracting minerals that shed new light on the ancient techniques have been found. Currently Pyrgos/Mavroraki seems to be the only settlement directly insisting on rocks containing copper oxides and sulphides which suggests a continuity of human habitation from the Preceramic Neolithic to the Middle Bronze Age. However, the slags of Pyrgos/Mavroraki offer many additional data about the Mediterranean copper production from the Chalcolithic until the Middle Bronze age, encompassing the most important period of the birth and evolution of metallurgy.The presence of slags until the bedrock made it necessary to carry out 14C dating of the charcoal taken from within the slags which gave four different calibrated datations: 8631-8291 BC, 4229-3960 BC, 2201-1948 BC, and 1937-1738 BC, demonstrating the ininterrupted activity of the site in copper processing. The results of the recent 14C investigations carried out by the CEDAD of Lecce for the ISPC-CNR, published in Scripta Cipria III, trace the extraction of copper in Cyprus to the end of the 5th and beginning of the 4th millennium BC, placing the island among the first copper producers in the Mediterranean. The 13 different datings carried out by the CEDAD of Lecce, added to those carried out in 2003 at the Chemistry laboratory of the Sapienza University of Rome, directed by Prof. Gilberto Calderoni, also testify that the site of Pyrgos / Mavroraki, investigated by the Italian Mission of the Italian National Council for Researches (CNR) since 1998, has had a continuous production of copper and bronze artefacts from the beginning of the Chalcolithic period (4200 BC) to the Middle Bronze Age II (around 1750 BC) when the site was abandoned after a devastating earthquake. The dating method is based on coal samples taken from furnaces and slag in pristine environment. A slag contained coal dated 8631-8291 BC, i.e. to the Preceramic Neolithic present in the first habitation layers of the Pyrgos/Mavroraki site, evidenced by the remains of houses, tools and artefacts. According to the theory of U. Fornhammar and H. Hammarström recently tested and published (https://exarc.net/ark:/88735/10619) the slag could be the tangible demonstration of the involuntary path towards the discovery of the metal, carried out by the inhabitants of the first village of Pyrgos positioned above a terrace with outcrops of carbonates of copper, while they roasted limestone blocks to obtain plastering mortar. The existence of this ancient copper mining and processing site in Cyprus is of historical significance, as it testify that the island has been perfectly capable of cultivating its deposits of minerals and extracting the metals since the beginning of the Chalcolithic period.
Results in Chemistry, 2024
Biogas is obtained from the breakdown of biomass by microorganisms and bacteria in the absence of oxygen. Biogas is considered a renewable source of energy, similar to solar energy and wind energy. Biogas can be produced from biomass or bio-waste; thus, it is environmentally friendly. Biogas is obtained in a suspended monoxide decomposition process by anaerobic bacteria or in a fermentation process of decomposable materials such as agricultural manure, sewage, municipal waste, green waste (gardens and parks), plant material and agricultural products. Biogas is a renewable natural energy source that leaves effective effects on nature and industries. This gas is produced from the decomposition of organic materials, including animal manure, food waste and sewage. Fertilizers and waste produce biogas through anaerobic digestion (ie without the presence of oxygen). Biogas is a mixture of gases generated by decaying biodegradable material without the presence of oxygen. Its main contents are 50–70 % of methane (CH4) by volume, 30–50 % of carbon dioxide (CO2), and traces of other gases, like hydrogen sulfide (H2S) and water vapor (H2O). CO2, H2S, and water vapor content in biogas may affect the performance and life of the energy conversion devices; consequently, their removal before end-use is essential for improving the quality of biogas. This combination is an ideal option for making renewable energy. The most important advantages of biogas (production of energy, reduction of the amount of discarded waste, reduction of pathogens, conversion of waste containing organic matter into high quality fertilizer, protection of vegetation, soil, water, increasing productivity in the field of livestock and agriculture) and It is also one of the disadvantages of biogas (incomplete and small technologies, containing impurities, the effect of temperature on biogas production, unsuitable for urban and dense areas, not affordable). For economical use of biogas, the fermentation process can be carried out under controlled conditions in a relatively simple device called a digestion reservoir. This review summarizes the current state-of-the-art and presents future perspectives related to the anaerobic digestion process for biogas production. Moreover, a historical retrospective of biogas sector from the early years of its development till its recent advancements give an outlook of the opportunities that are opening up for process optimization.
American Journal of Comparative Law, 2021
This Article investigates how contemporary laws of war rationalize civilian deaths. I concentrate on two specific legal constructions in warfare: the definition of civilian/combatant and the principle of distinction. (The categories of civilian and combatant should be understood as dialogically constitutive and not entirely distinct. In addition, the category of "civilian" is a modern one and premodern legal sources often do not use one term to refer to noncombatants.) I focus on two significant parties in contemporary warfare: al-Qāʿidah (aka Al-Qaeda) and the U.S. military. Al-Qāʿidah diverges from orthodox Islamic law on these two legal issues, while remaining within the Islamic legal tradition. To scrutinize the nature of this divergence, I compare al-Qāʿidah's legal reasoning to the legal reasoning of the U.S. military. I demonstrate that the U.S. military diverges from orthodox international law in ways that parallel how al-Qāʿidah diverges from orthodox Islamic law. Specifically, both the U.S. military and al-Qāʿidah elide orthodox categories of civilians and expand the category of combatant, primarily by rendering civilians as probable combatants. Based on this comparative analysis, I argue that the legal reasoning of al-Qāʿidah (and other militant Islamist groups) is as secular as it is Islamic; I call this fusion secularislamized law.
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