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1.
We study refined and motivic wall-crossing formulas in N=2{{\mathcal N}=2} supersymmetric gauge theories with SU(2) gauge group and N
f
< 4 matter hypermultiplets in the fundamental representation. Such gauge theories provide an excellent testing ground for
the conjecture that “refined = motivic.” 相似文献
2.
We analyze the dependence of heavy quark free energies on the baryon chemical potential μ b in 2-flavor QCD by performing a 6th order Taylor expansion in the chemical potential which circumvents the sign problem.
The bare quark mass at
corresponds to a pion mass of about 770 MeV and is thus not in the range of physical quark masses but the quark mass dependence
is known to be small above Tc. At Nτ = 4 the lattices are coarse, however, we are using improved (p4 staggered) fermions. The Taylor expansion coefficients of
color singlet and color averaged free energies are calculated and from this the expansion coefficients for the corresponding
screening masses are determined. We find that for small μ b the free energies of a static quark-antiquark pair decrease in a medium with a net excess of quarks and that screening is
well described by a screening mass which increases with increasing μ b. The μ b-dependent corrections to the screening masses are well described by perturbation theory for T ≳ 2 Tc. In particular, we find for all temperatures above Tc that the expansion coefficients for singlet and color averaged screening masses differ by a factor 2.
PACS. 11.15.Ha, 11.10.Wx, 12.38Gc, 12.38.Mh 相似文献
3.
We study SU(2) lattice gauge theory with four species ( Nf = 4) of light dynamical fermions by microcanonical simulation methods. Relatively large lattices, long runs and small quark masses are considered. On a 8 3 × 16 lattice is measured and good evidence for asymptotic freedom with fermion feedback is found. The scaling window begins at β = 4/ g2 ≈ 1.85. On a 12 3 × 6 lattice SU(2) thermodynamics is studied systematically. The chiral symmetry restoration transition is found at β = 1.925 ± .025. The crossover from hadronic matter to the quark-gluon plasma is abrupt. 相似文献
4.
From the overlap lattice quark propagator calculated in the Landau gauge,we determine the quark chiral condensate by fitting operator product expansion formulas to the lattice data.The quark propagators are computed on domain wall fermion configurations generated by the RBC-UKQCD Collaborations with N_f = 2 + 1flavors.Three ensembles with different light sea quark masses are used at one lattice spacing 1/a = 1.75(4) Ge V.We obtain ψψ (2 GeV)MS =(-304(15)(20) MeV)~3in the SU(2) chiral limit. 相似文献
5.
Results are presented from a numerical study of lattice QCD with gauge group SU(2) and two flavors of Wilson fermion at non-zero quark chemical potential μ ≫ T. Studies of the equation of state, the superfluid condensate, and the Polyakov line all suggest that in addition to the low-density
phase of Bose-condensed diquark baryons, there is a deconfined phase at higher quark density in which quarks form a degenerate
system, whose Fermi surface is only mildly disrupted by Cooper pair condensation. 相似文献
6.
We study SU(2) lattice gauge theory with two flavors of Wilson fermion at non-zero chemical potential μ and low temperature on a 8 3×16 system. We identify three régimes along the μ-axis. For μ≲m π/2 the system remains in the vacuum phase and all physical observables considered remain essentially unchanged. The intermediate régime is characterised by a non-zero diquark condensate and an associated increase in the baryon density, consistent with what is expected for Bose–Einstein condensation of tightly bound diquarks. We also observe screening of the static quark potential here. In the high-density deconfined régime we find a non-zero Polyakov loop and a strong modification of the gluon propagator, including significant screening in the magnetic sector in the static limit, which must have a non-perturbative origin. The behaviour of thermodynamic observables and the superfluid order parameter are consistent with a Fermi surface disrupted by a BCS diquark condensate. The energy per baryon as a function of μ exhibits a minimum in the deconfined régime, implying that macroscopic objects such as stars formed in this theory are largely composed of quark matter. 相似文献
7.
The running coupling and the Kugo-Ojima parameter of unquenched lattice Landau gauge are simulated and compared with the continuum
theory. Although the running coupling measured by the ghost and gluon dressing function is infrared suppressed, the running
coupling has a maximum of α 0 ∼ 2 − 2.5 at around q = 0.5 GeV irrespective of the fermion actions (Wilson fermions and Kogut-Susskind (KS) fermions). The Kugo-Ojima parameter
c which saturated to about 0.8 in quenched simulations becomes consistent with 1 in the MILC configurations produced with the
use of the Asqtad action, after averaging the dependence on polarization directions caused by the asymmetry of the lattice.
The presence of the correction factor 1 + c
1/ q
2 in the running coupling depends on the lattice size and the sea quark mass. In the large lattice size and small sea quark
mass, c
1 is confirmed of the order of a few GeV. The MILC configuration of a = 0.09 fm suggests also the presence of dimension-4 condensates with a sign opposite to the dimension-2 condensates. The
gluon propagator, the ghost propagator, and the running coupling are compared with recent pQCD results including an anomalous
dimension of fields up to the four-loop level. 相似文献
8.
The studies of superconductivity, dual superconductivity and color superconductivity have been undertaken through the breaking
of supersymmetric gauge theories which automatically incorporate the condensation of monopoles and dyons leading to confining
and superconducting phases. Constructing the total effective Lagrangian of N=2 SU(2) gauge theory with N
f
=2 quark multiplets and quark chemical potential at classical and quantum levels, it has been demonstrated that baryon number
symmetry is spontaneously broken as a consequence of the SU(2) strong gauge dynamics and the color superconductivity dynamically takes space at the non-SUSY vacuum. 相似文献
9.
Let f(ϕ) be a positive continuous function on 0 ≤ϕ≤Θ, where Θ≤ 2 π, and let ξ be the number of two-dimensional lattice points in
the domain Π
R
( f) between the curves r=( R+ c
1/ R) f(ϕ) and r=( R+ c
2/ R) f(ϕ), where c
1< c
2 are fixed. Randomizing the function f according to a probability law P, and the parameter R according to the uniform distribution μ
L
on the interval [ a
1
L, a
2
L], Sinai showed that the distribution of ξ under P×μ
L
converges to a mixture of the Poisson distributions as L→∞. Later Major showed that for P-almost all f, the distribution of ξ under μ
L
converges to a Poisson distribution as L→∞. In this note, we shall give shorter and more transparent proofs to these interesting theorems, at the same time extending
the class of P and strengthening the statement of Sinai.
Received: 15 June 1999 / Accepted: 11 February 2000 相似文献
10.
The strange form factors of the nucleon are studied in a two-component model consisting of a three-quark intrinsic structure
surrounded by a meson cloud. A comparison with the available experimental world data from the SAMPLE, PVA4, HAPPEX and G0
Collaborations shows a good overall agreement. It is shown that the strangeness contribution to the electric and magnetic
form factors is of the order of a few percent. In particular, the strange quark contribution to the charge radius is small
〈 r
2
s〉 E = 0.005 fm^2 and to the magnetic moment it is positive μ s = 0.315 μ N . 相似文献
11.
We examine the predictions of gauge theories with colour excitation for the process pp → μ
+
μ
−
X. Relative to the predictions of quark parton model (with three colours) we find enhancements as large as a factor 3 – 4 for
the cross-section M
3
d
2
σ/dMdy| y=0 in the region 0·03 ≲ M/√ s ≲ 0·2 at √ s=62 GeV, M being the invariant mass and y the rapidity of the muon pair. We study the sensitivity of this result to the colour gluon mass and the underlying parametrisation
of the quark and gluon distribution functions. 相似文献
12.
Several lattice collaborations performing simulations with 2+1 light dynamical quarks have experienced difficulties in fitting their data with standard N
f = 3 chiral expansions at next-to-leading order, yielding low values of the quark condensate and/ or the decay constant in the N
f = 3 chiral limit. A reordering of these expansions seems required to analyse these data in a consistent way. We discuss such a reordering, known as Resummed Chiral Perturbation Theory, in the case of pseudoscalar masses and decay constants, pion and kaon electromagnetic form factors and K
ℓ3 form factors. We show that it provides a good fit of the recent results of two lattice collaborations (PACS-CS and RBC/UKQCD). We describe the emerging picture for the pattern of chiral symmetry breaking, marked by a strong dependence of the observables on the strange quark mass and thus a significant difference between chiral symmetry breaking in the N
f = 2 and N
f =3 chiral limits. We discuss the consequences for the ratio of decay constants F
K
/F
π and the K ℓ3 form factor at vanishing momentum transfer. 相似文献
13.
A gauge model for the weak interactions of the leptons ( v
e, e, μ, ν μ) and the quarks ( q
p, q n, qλ, q
p′) is presented in which deviations from universality, such as the Cabibbo suppression, are explicitly and spontaneously generated.
The gauge group is, to begin with SU(4). There are three quartets of Higgs scalars with suitable vacuum expectation values,
sufficient and necessary to give masses to all gauge bosons. It turns out that this gauge group is too ‘large’ and fails to
account for many observed symmetries of weak interactions, especially electron-muon symmetry. This symmetry corresponds to
a discrete transformation R which is an element of SU(4). To accommodate it, the gauge group is restricted to the subgroup of SU(4) which commutes with R. There are now 7 gauge bosons, 4 charged and 3 neutral. One pair of charged bosons is necessarily heavier than the other
pair (denoted W
±) and two neutrals are necessarily heavier than the third ( W
0). The electron and the muon become massive while the neutrinos and the quark fields remain massless.
The dominant charged weak currents coupling to W
± have e-μ universality and Cabibbo universality for both of which R-symmetry is essential—the Cabibbo angle is a simple function of the vacuum expectation values. The same symmetry ensures e-μ symmetry and the absence of flavour-changing components in the neutral currents. The currents coupling to the heavier gauge
bosons break all these symmetries but these bosons can be made arbitrarily heavy and so are relevant only in the domain of
‘ultraweak’ interactions.
The Cabibbo angle ϑ
c itself is determined by minimising a very general class of Higgs potentials, leading to a numerical value ϑ
c = ± π/8, | tan ϑ
c | = √2 − 1 (an alternative solution | tan ϑ
c | = (√2+1) is rejected), independent of the parameters and of the precise form of the potential. This is the ‘bare’ ϑ
c; in low energy/momentum transfer processes, this value is renormalised by the structure of the hadrons. A model is given
for this renormalisation which reduces the renormalised value of | tan ϑ
c | to about 0.2–0.3 from the bare value 0.41. Recent data on highly inelastic neutrino interactions are shown to be not inconsistent
with | tan ϑ
c | = 0.4. 相似文献
14.
Deconfinement phase transition due to the disappearance of confining colorelectric field correlators is described using a
nonperturbative equation of state. The resulting transition temperature T
c
(μ) at any chemical potential μ is expressed in terms of the change of the gluon condensate Δ G
2 and absolute value of the Polyakov loop L
fund( T
c
), which is known from the lattice and analytic data, and is in good agreement with the lattice data for Δ G
2 ≈ 0.0035 GeV 4; e.g., T
c
(0) = 0.27, 0.19, and, 0.17 GeV for n
f
= 0, 2, and 3, respectively.
The text was submitted by the authors in English. 相似文献
15.
2-( p- N, N-dimethylaminostyryl)benzoxazole ( OS), 2-( p- N, N-dimethylaminostyryl)-benzothiazole ( SS) and 2-( p- N, N-dimethylaminostyryl)naphtiazole ( PS) were prepared and their absorption and fluorescence spectra were measured in various solvents at room temperature. On the basis of the solvatochromic behavior the ground state (μ g) and excited state (μ e) dipole moments of these pN,N-dimethylaminostyryl derivatives were evaluated. The dipole moments (μ g and μ e) were estimated from solvatochromic shifts of absorption and fluorescence spectra as function of the dielectric constant (ɛ) and refractive index ( n) of applied solvents. The absorption spectra only slightly are affected by the solvent polarity in contrast to the fluorescence spectra that are highly solvatochromic and display a large Stokes shift. The analysis of the solvatochromic behavior of the fluorescence spectra as function of Δ f (ɛ, n) revealed that the emission occurs from a high polarity excited state. The large dipole moment change along with the strongly red-shifted fluorescence, as the solvent polarity is increased, demonstrate the formation of an intramolecular charge transfer state (ICT). Compounds under the study were used as fluorescence probes for monitoring the kinetics of polymerization. The study on the changes in fluorescence intensity and spectroscopic shifts of studied compounds were carried out during thermally initiated polymerization of methyl methacrylate (MMA) and during photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-1,3-diol triacrylate (TMPTA). 相似文献
16.
A mathematical method is presented for solving the Schr?dinger equation for a system of identical body forces. The N-body forces are more easily introduced and treated within the hyperspherical harmonics. The problem of the N-body potential has been used at the level of both classical and quantum mechanics.
The hypercentral interacting potential is assumed to depend on the hyperradius x = (ξ 12 + ξ 22 + ⋯ + ξ N−12) 1/2 only, where ξ 1,ξ 2,…,ξ N−1 are Jacobi relative coordinates which are functions of N-particle relative positions r12, r23,…, rN1. The problem of the harmonic oscillator and the Coulomb-type potential has been widely studied in different contexts.
Using the N-body potential V( x) = ax2 + bx − ( c/ x) as an example, and assuming an ansatz for the eigenfunction, an exact analytical solution of the Schr?dinger equation for
an N-body system in three dimensions is obtained. This method is also applicable to some other types of potentials for N-identical interacting particles. 相似文献
17.
The changes in the action (and thus the vacuum conservation amplitudes) in the proper-time representation are found for an
accelerated mirror interacting with scalar and spinor vacuum fields in 1+1 space. They are shown to coincide to within a factor
of e
2 with changes in the action of electric and scalar charges accelerated in 3+1 space. This coincidence is attributed to the
fact that the Bose and Fermi pairs emitted by a mirror have the same spins 1 and 0 as do the photons and scalar quanta emitted
by charges. It is shown that the propagation of virtual pairs in 1+1 space can be described by the causal Green’s function
Δ f( z,μ) of the wave equation for 3+1 space. This is because the pairs can have any positive mass and their propagation function
is represented by an integral of the causal propagation function of a massive particle in 1+1 space over mass which coincides
with Δ f( z,μ). In this integral the lower limit μ is chosen small, but nonzero, to eliminate the infrared divergence. It is shown that the real and imaginary parts of the
change in the action are related by dispersion relations, in which a mass parameter serves as the dispersion variable. They
are a consequence of the same relations for Δ f( z, μ). Therefore, the emergence of a real part in the change in the action is a direct consequence of causality, according to
which Re Δ f( z,μ)≠0 only for timelike and lightlike intervals.
Zh. éksp. Teor. Fiz. 116, 1523–1538 (November 1999) 相似文献
18.
The mass spectrum of pure Yang–Mills theory in 3+1 dimensions is discussed for an arbitrary simple gauge algebra within a
quasigluon picture. The general structure of the low-lying gluelump and two-quasigluon glueball spectrum is shown to be common
to all algebras, while the lightest C=− three-quasigluon glueballs only exist when the gauge algebra is A
r≥2, that is, in particular,
\mathfrak su( N 3 3)\mathfrak{su}(N\geq3). Higher-lying C=− glueballs are shown to exist only for the A
r≥2, D odd−r≥4 and E 6 gauge algebras. The shape of the static energy between adjoint sources is also discussed assuming the Casimir scaling hypothesis
and a funnel form; it appears to be gauge-algebra dependent when at least three sources are considered. As a main result,
the present framework’s predictions are shown to be consistent with available lattice data in the particular case of an
\mathfrak su( N)\mathfrak{su}(N) gauge algebra within ’t Hooft’s large- N limit. 相似文献
19.
A field model for a quark and an antiquark binding is described. Quarks interact via a gauge unparticle (“ungluon”). The model
is formulated in terms of Lagrangian which features the source field S( x) which becomes a local pseudo-Goldstone field of conformal symmetry — the pseudodilaton mode and from which the gauge non-primary
unparticle field is derived by B
μ( x) ∼ ∂ μ
S( x). Because the conformal sector is strongly coupled, the mode S( x) may be one of new states accessible at high energies. We have carried out an analysis of the important quantity that enters
in the “ungluon” exchange pattern — the “ungluon” propagator. 相似文献
20.
Chiral symmetry breaking may exhibit significantly different patterns in two chiral limits: N f=2 massless flavours (m u=m d=0, m s physical) and N f=3 massless flavours (m u=m d=m s=0). Such a difference may arise due to vacuum fluctuations of ss̄ pairs related to the violation of the Zweig rule in the
scalar sector, and it could yield numerical competition between contributions counted as leading and next-to-leading order
in the chiral expansions of the observables. We recall and extend resummed chiral perturbation theory (ReχPT), a framework
that we introduced previously to deal with such instabilities: it requires a more careful definition of the relevant observables
and their one-loop chiral expansions. We analyse the amplitudes for low-energy ππ and πK scatterings within ReχPT, which we
match in subthreshold regions with dispersive representations obtained from the solutions of the Roy and Roy–Steiner equations.
Using a frequentist approach, we constrain the quark mass ratio as well as the quark condensate and the pseudoscalar decay
constant in the N f=3 chiral limit. The results mildly favour significant contributions of vacuum fluctuations suppressing the N f=3 quark condensate compared to its N f=2 counterpart. 相似文献
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