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Sep 18, 2013
09/13

by
Tomas Brauner

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We study the relativistic BCS-BEC crossover within a class of Nambu-Jona-Lasinio type models, including arbitrary Lorentz-scalar pairing channels. Using the mean-field approximation we investigate spectral properties of the collective bosonic excitations in the superfluid phase, with particular attention to the Nambu--Goldstone bosons of the broken symmetry. This is a first step towards a systematic improvement of the mean-field approximation by including the fluctuation effects. The general...

Source: http://arxiv.org/abs/0803.2422v2

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Sep 21, 2013
09/13

by
Tomas Brauner

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We analyze the effects of finite chemical potential on spontaneous breaking of internal symmetries within the class of relativistic field theories described by the linear sigma model. Special attention is paid to the emergence of ``abnormal'' Goldstone bosons with quadratic dispersion relation. We show that their presence is tightly connected to nonzero density of the Noether charges, and formulate a general counting rule. The general results are demonstrated on an SU(3)xU(1) invariant model...

Source: http://arxiv.org/abs/hep-ph/0508011v2

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Sep 21, 2013
09/13

by
Tomas Brauner

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I report the results of a series of works on the phase diagram of theories with a different number of colors and/or quarks in a different representation than in QCD. Similarities as well as differences as compared to the real world are pointed out, focusing in particular on the interplay of confinement and chiral symmetry breaking. It will be argued that recent lattice data may provide us with a clue to understand deconfinement in cold dense quark matter.

Source: http://arxiv.org/abs/1011.1111v1

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Sep 22, 2013
09/13

by
Tomas Brauner

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Spontaneous symmetry breaking is a general principle, that constitutes the underlying concept of a vast number of physical phenomena ranging from ferromagnetism and superconductivity in condensed matter physics to the Higgs mechanism in the standard model of elementary particles. I focus on manifestations of spontaneously broken symmetries in systems that are not Lorentz invariant, which include both, nonrelativistic systems as well as relativistic systems at nonzero density, providing a...

Source: http://arxiv.org/abs/1001.5212v2

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60

Sep 18, 2013
09/13

by
Tomas Brauner

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This is the introduction to the PhD thesis, defended in June 2006. In the original form it was appended with the reprints of the author's published papers, and is to be regarded as their summary. Full details may be found in the quoted papers.

Source: http://arxiv.org/abs/hep-ph/0606300v1

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Sep 20, 2013
09/13

by
Tomas Brauner

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We construct the chiral perturbation theory for two-color QCD with two quark flavors as an effective theory on the SO(6)/SO(5) coset space. This formulation turns out to be particularly useful for extracting the physical content of the theory when finite baryon and isospin chemical potentials are introduced, and Bose--Einstein condensation sets on.

Source: http://arxiv.org/abs/hep-ph/0601010v1

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Sep 23, 2013
09/13

by
Tomas Brauner

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We investigate spin-one color superconductivity of a single quark flavor using the Ginzburg-Landau theory. First we examine the classic analysis of Bailin and Love and show that by restricting to the so-called inert states, it misses the true ground state in a part of the phase diagram. This suggests the use of the more general, noninert states in particular within three-flavor quark matter where the color neutrality constraint imposes stress on the spin-one pairing and may disfavor the...

Source: http://arxiv.org/abs/0810.3481v2

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Sep 22, 2013
09/13

by
Tomas Brauner

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We investigate the thermodynamics of a pion gas within the O(N) model in the 1/N expansion. Using the auxiliary field technique, we compute the effective potential up to the next-to-leading order (NLO) and show that it can be renormalized in a temperature-independent manner. The crucial step for the consistency of the calculation turns out to be the elimination of the auxiliary field prior to renormalization. Subsequently, we solve the NLO gap equation for the chiral condensate as a function of...

Source: http://arxiv.org/abs/0812.0404v1

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Sep 20, 2013
09/13

by
Tomas Brauner

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We investigate spontaneous symmetry breaking within the linear sigma model with the SU(2)xU(1) internal symmetry at finite chemical potential, which was suggested as a model for kaon condensation in the CFL phase of dense quark matter. One-loop corrections to the scalar field effective potential as well as its propagator are calculated. Particular attention is paid to the type-II Goldstone boson that appears in the Bose--Einstein condensed phase. Furthermore, we show that the type-I Goldstone...

Source: http://arxiv.org/abs/hep-ph/0607102v2

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Sep 19, 2013
09/13

by
Tomas Brauner

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We investigate spontaneous symmetry breaking in Lorentz-noninvariant theories. Our general discussion includes relativistic systems at finite density as well as intrinsically nonrelativistic systems. The main result of the paper is a direct proof that nonzero density of a non-Abelian charge in the ground state implies the existence of a Goldstone boson with nonlinear (typically, quadratic) dispersion law. We show that the Goldstone boson dispersion relation may in general be extracted from the...

Source: http://arxiv.org/abs/hep-ph/0701110v2

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Sep 21, 2013
09/13

by
Tomas Brauner; Jiri Hosek

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We argue in favor of dynamical mass generation in an SU(2)xU(1) electroweak model with two complex scalar doublets with ordinary masses. The masses of leptons and quarks are generated by ultraviolet-finite non-perturbative solutions of the Schwinger-Dyson equations for full fermion propagators with self-consistently modified scalar boson exchanges. The W and Z boson masses are expressed in terms of spontaneously generated fermion proper self-energies in the form of sum rules. The model predicts...

Source: http://arxiv.org/abs/hep-ph/0407339v1

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3.0

Jun 29, 2018
06/18

by
Tomas Brauner; Naoki Yamamoto

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The Chiral Soliton Lattice (CSL) is a state with a periodic array of topological solitons that spontaneously breaks parity and translational symmetries. Such a state is known to appear in chiral magnets. We show that CSL also appears as a ground state of quantum chromodynamics at nonzero chemical potential in a magnetic field. By analyzing the fluctuations of the CSL, we furthermore demonstrate that in strong but achievable magnetic fields, charged pions undergo Bose-Einstein condensation. Our...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology, Condensed Matter, Strongly...

Source: http://arxiv.org/abs/1609.05213

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6.0

Jun 30, 2018
06/18

by
Tomas Brauner; Sergej Moroz

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We classify effective actions for Nambu-Goldstone (NG) bosons assuming absence of anomalies. Special attention is paid to Lagrangians invariant only up to a surface term, shown to be in a one-to-one correspondence with Chern-Simons (CS) theories for unbroken symmetry. Without making specific assumptions on spacetime symmetry, we give explicit expressions for these Lagrangians, generalizing the Berry and Hopf terms in ferromagnets. Globally well-defined matrix expressions are derived for...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology, Statistical Mechanics, Condensed...

Source: http://arxiv.org/abs/1405.2670

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Sep 18, 2013
09/13

by
Tomas Brauner; Jiri Hosek

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We consider a model with global Abelian chiral symmetry of two massless fermion fields interacting with a complex massive scalar field. We argue that the Schwinger-Dyson equations for the fermion and boson propagators admit ultraviolet-finite chiral-symmetry-breaking solutions provided the Yukawa couplings are large enough. The fermions acquire masses and the elementary excitations of the complex scalar field are the two real spin-zero particles with different masses. As a necessary consequence...

Source: http://arxiv.org/abs/hep-ph/0505231v1

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5.0

Jun 30, 2018
06/18

by
Tomas Brauner; Saurabh Kadam

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The ground state of quantum chromodynamics in sufficiently strong external magnetic fields and at moderate baryon chemical potential is a chiral soliton lattice (CSL) of neutral pions. We investigate the interplay between the CSL structure and dynamical electromagnetic fields. Our main result is that in presence of the CSL background, the two physical photon polarizations and the neutral pion mix, giving rise to two gapped excitations and one gapless mode with a nonrelativistic dispersion...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1701.06793

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Sep 23, 2013
09/13

by
Haruki Watanabe; Tomas Brauner

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The low-energy physics of systems with spontaneous symmetry breaking is governed by the associated Nambu-Goldstone (NG) bosons. While NG bosons in Lorentz-invariant systems are well understood, the precise characterization of their number and dispersion relations in a general quantum many-body system is still an open problem. An inequality relating the number of NG bosons and their dispersion relations to the number of broken symmetry generators was found by Nielsen and Chadha. In this paper,...

Source: http://arxiv.org/abs/1109.6327v2

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49

Sep 23, 2013
09/13

by
Hiroaki Abuki; Tomas Brauner

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We investigate the 1/N expansion proposed recently as a strategy to include quantum fluctuation effects in the nonrelativistic, attractive Fermi gas at and near unitarity. We extend the previous results by calculating the next-to-leading order corrections to the critical temperature along the whole BCS-BEC crossover. We demonstrate explicitly that the extrapolation from the mean-field approximation, based on the $1/N$ expansion, provides a useful approximation scheme only on the BCS side of the...

Source: http://arxiv.org/abs/0810.0400v2

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Sep 24, 2013
09/13

by
Haruki Watanabe; Tomáš Brauner

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Unbroken continuous translational invariance is often taken as a basic assumption in discussions of spontaneous symmetry breaking (SSB), which singles out SSB of translational invariance itself as an exceptional case. We present a framework which allows us to treat translational invariance on the same footing as other symmetries. It is shown that existing theorems on SSB can be straightforwardly extended to this general case. As a concrete application, we analyze the Nambu-Goldstone modes in a...

Source: http://arxiv.org/abs/1112.3890v2

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Jul 20, 2013
07/13

by
Hiroaki Abuki; Tomáš Brauner

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We revisit the issue of color neutrality in effective model descriptions of dense quark matter based on global color symmetry. While the equilibrium thermodynamics of such models is now well understood, we examine the collective modes, focusing on the fluctuations of the order parameter. We point out that the constraint of color neutrality must be carefully generalized in order to obtain physically consistent and well-defined results. Particularly important is that the collective modes...

Source: http://arxiv.org/abs/1203.1705v1

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8.0

Jun 30, 2018
06/18

by
Tomáš Brauner; Haruki Watanabe

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It has been long known that when spacetime symmetry is spontaneously broken, some of the broken generators may not give rise to independent gapless, Nambu-Goldstone excitations. We provide two complementary viewpoints of this phenomenon. On the one hand, we show that the corresponding field degrees of freedom have the same symmetry transformation properties as massive, matter fields. The "inverse Higgs constraints", sometimes employed to eliminate these modes from the theory, are...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology, Statistical Mechanics, Condensed...

Source: http://arxiv.org/abs/1401.5596

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51

Sep 22, 2013
09/13

by
Jens O. Andersen; Tomas Brauner

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We investigate the properties of cold dense quark matter composed of two colors and two flavors of light quarks. In particular, we perform the first model calculation of the full phase diagram at nonzero baryon and isospin density, thus matching the model-independent predictions of chiral perturbation theory at low density to the conjectured phase structure at high density. We confirm the presence of the Fulde-Ferrell (FF) phase in the phase diagram and study its dependence on the tunable...

Source: http://arxiv.org/abs/1001.5168v2

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5.0

Jun 29, 2018
06/18

by
Tomas Brauner; Xu-Guang Huang

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We revisit the suggestion that charged rho-mesons undergo Bose-Einstein condensation in isospin-rich nuclear matter. Using a simple version of the Nambu-Jona-Lasinio (NJL) model, we conclude that rho-meson condensation is either avoided or postponed to isospin chemical potentials much higher than the rho-meson mass as a consequence of the repulsive interaction with the preformed pion condensate. In order to support our numerical results, we work out a linear sigma model for pions and...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology, Nuclear Theory

Source: http://arxiv.org/abs/1610.00426

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132

Jul 20, 2013
07/13

by
Jens O. Andersen; Tomas Brauner

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We study relativistic Bose-Einstein condensation at finite density and temperature using the linear sigma model in the one-particle-irreducible 1/N-expansion. We derive the effective potential to next-to-leading (NLO) order and show that it can be renormalized in a temperature-independent manner. As a particular application, we study the thermodynamics of the pion gas in the chiral limit as well as with explicit symmetry breaking. At nonzero temperature we solve the NLO gap equation and show...

Source: http://arxiv.org/abs/0804.4604v2

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40

Sep 18, 2013
09/13

by
Petr Benes; Tomas Brauner; Jiri Hosek

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We consider a model with anomaly-free Abelian gauge axial-vector symmetry, which is intended to mimic the standard electroweak gauge chiral SU(2)_L x U(1)_Y theory. Within this model we demonstrate: (1) Strong Yukawa interactions between massless fermion fields and a massive scalar field carrying the axial charge generate dynamically the fermion and boson proper self-energies, which are ultraviolet-finite and chirally noninvariant. (2) Solutions of the underlying Schwinger-Dyson equations found...

Source: http://arxiv.org/abs/hep-ph/0605147v3

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Sep 23, 2013
09/13

by
Haruki Watanabe; Tomáš Brauner; Hitoshi Murayama

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Nicolis and Piazza have recently pointed out the existence of Nambu-Goldstone-like excitations in relativistic systems at finite density, whose gap is exactly determined by the chemical potential and the symmetry algebra. We show that the phenomenon is much more general than anticipated and demonstrate the presence of such modes in a number of systems from (anti)ferromagnets in magnetic field to superfluid phases of quantum chromodynamics. Furthermore, we prove a counting rule for these massive...

Source: http://arxiv.org/abs/1303.1527v2

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Sep 18, 2013
09/13

by
Petr Benes; Tomas Brauner; Adam Smetana

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We present a new mechanism for electroweak symmetry breaking (EWSB) based on a strong Yukawa dynamics. We consider an SU(2)_L x U(1)_Y gauge invariant model endowed with the usual Standard model fermion multiplets and with two massive scalar doublets. We show that, unlike in the Standard model, EWSB is possible even with vanishing vacuum expectation values of the scalars. Such EWSB is achieved dynamically by means of the (presumably strong) Yukawa couplings and manifests itself by the emergence...

Source: http://arxiv.org/abs/0806.2565v3

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Sep 22, 2013
09/13

by
Hiroaki Abuki; Tomas Brauner; Harmen J. Warringa

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We argue that using an equilibrated gas of neutrinos it is possible to probe the phase diagram of QCD for finite isospin and small baryon chemical potentials. We discuss this region of the phase diagram in detail and demonstrate that for large enough neutrino densities a Bose-Einstein condensate of positively charged pions arises. Moreover, we show that for nonzero neutrino density the degeneracy in the lifetimes and masses of the charged pions is lifted.

Source: http://arxiv.org/abs/0901.2477v2

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Sep 19, 2013
09/13

by
Tomas Brauner; Jin-yi Pang; Qun Wang

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Spin-one color superconductor is a viable candidate phase of dense matter in the interiors of compact stars. Its low-energy excitations will influence the transport properties of such matter and thus have impact on late-stage evolution of neutron stars. It also provides a good example of spontaneous symmetry breaking with rich breaking patterns. In this contribution, we reanalyze the phase diagram of a spin-one color superconductor and point out that a part of it is occupied by noninert states,...

Source: http://arxiv.org/abs/0909.4201v1

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Jul 19, 2013
07/13

by
Tian Zhang; Tomas Brauner; Dirk H. Rischke

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We investigate the properties of hot and/or dense matter in QCD-like theories with quarks in a (pseudo)real representation of the gauge group using the Nambu-Jona-Lasinio model. The gauge dynamics is modeled using a simple lattice spin model with nearest-neighbor interactions. We first keep our discussion as general as possible, and only later focus on theories with adjoint quarks of two or three colors. Calculating the phase diagram in the plane of temperature and quark chemical potential, it...

Source: http://arxiv.org/abs/1005.2928v2

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Sep 19, 2013
09/13

by
Jin-yi Pang; Tomas Brauner; Qun Wang

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We investigate the collective excitations in spin-one color superconductors. We classify the Nambu--Goldstone modes by the pattern of spontaneous symmetry breaking, and then use the Ginzburg--Landau theory to derive their dispersion relations. These soft modes play an important role for the low-energy dynamics of the system such as the transport phenomena and hence are relevant for late-stage evolution of neutron stars. In the case of the color-spin-locking phase, we use a functional technique...

Source: http://arxiv.org/abs/1010.1986v1

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Jun 27, 2018
06/18

by
Jens O. Andersen; Tomas Brauner; William R. Naylor

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Ab initio numerical simulations of the thermodynamics of dense quark matter remain a challenge. Apart from the infamous sign problem, lattice methods have to deal with finite volume and discretization effects as well as with the necessity to introduce sources for symmetry-breaking order parameters. We study these artifacts in the Polyakov-loop-extended Nambu-Jona-Lasinio model, and compare its predictions to existing lattice data for cold and dense two-color matter with two flavors of Wilson...

Topics: High Energy Physics - Phenomenology, High Energy Physics - Lattice

Source: http://arxiv.org/abs/1505.05925

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Jun 30, 2018
06/18

by
Tomas Brauner; Solomon Endlich; Alexander Monin; Riccardo Penco

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We extend the notion of general coordinate invariance to many-body, not necessarily relativistic, systems. As an application, we investigate nonrelativistic general covariance in Galilei-invariant systems. The peculiar transformation rules for the background metric and gauge fields, first introduced by Son and Wingate in 2005 and refined in subsequent works, follow naturally from our framework. Our approach makes it clear that Galilei or Poincare symmetry is by no means a necessary prerequisite...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology, Strongly Correlated Electrons,...

Source: http://arxiv.org/abs/1407.7730

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Sep 24, 2013
09/13

by
Tian Zhang; Tomáš Brauner; Aleksi Kurkela; Aleksi Vuorinen

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We study the thermodynamics of two-color QCD at high temperature and/or density using a dimensionally reduced superrenormalizable effective theory, formulated in terms of a coarse grained Wilson line. In the absence of quarks, the theory is required to respect the Z(2) center symmetry, while the effects of quarks of arbitrary masses and chemical potentials are introduced via soft Z(2) breaking operators. Perturbative matching of the effective theory parameters to the full theory is carried out...

Source: http://arxiv.org/abs/1112.2983v2

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Sep 23, 2013
09/13

by
Tomas Brauner; Olli Taanila; Anders Tranberg; Aleksi Vuorinen

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We analyze the temperature dependence of CP violation effects in the Standard Model by determining the effective action of its bosonic fields, obtained after integrating out the fermions from the theory and performing a covariant gradient expansion. We find non-vanishing CP violating terms starting at the sixth order of the expansion, albeit only in the C odd/P even sector, with coefficients that depend on quark masses, CKM matrix elements, temperature and the magnitude of the Higgs field. The...

Source: http://arxiv.org/abs/1110.6818v2

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3.0

Jun 30, 2018
06/18

by
Jens O. Andersen; Tomas Brauner; Christoph P. Hofmann; Aleksi Vuorinen

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The low-energy and low-momentum dynamics of systems with a spontaneously broken continuous symmetry is dominated by the ensuing Nambu-Goldstone bosons. It can be conveniently encoded in a model-independent effective field theory whose structure is fixed by symmetry up to a set of effective coupling constants. We construct the most general effective Lagrangian for the Nambu-Goldstone bosons of spontaneously broken global internal symmetry up to the fourth order in derivatives. Rotational...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology, Strongly Correlated Electrons,...

Source: http://arxiv.org/abs/1406.3439

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6.0

Jun 29, 2018
06/18

by
Tomáš Brauner; Tuomas V. I. Tenkanen; Anders Tranberg; Aleksi Vuorinen; David J. Weir

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We derive an effective dimensionally reduced theory for the Standard Model augmented by a real singlet scalar. We treat the singlet as a superheavy field and integrate it out, leaving an effective theory involving only the Higgs and $\mathrm{SU}(2)_\mathrm{L} \times \mathrm{U}(1)_Y$ gauge fields, identical to the one studied previously for the Standard Model. This opens up the possibility of efficiently computing the order and strength of the electroweak phase transition, numerically and...

Topic: High Energy Physics - Phenomenology

Source: http://arxiv.org/abs/1609.06230