1. PhysOrg: This site is the ideal place to get your daily physics news fix.
2. Physics Today News Picks: Check in with this blog regularly to read about the latest news articles that relate to the world of physics.
3. The X-Journals: Bookmark this blog to follow some of the amazing new technologies that are emerging in fields like computer science and physics that will shape the world of tomorrow.
4. The Physics ArXiv Blog: On this blog you’ll find a collection of the best content from the online forum called the Physics arXiv on which scientists post early versions of their latest ideas.
5. FQXi Community: Here you can read a collection of entries on blogs in the FQXi Community, or the Foundational Questions Institute.

Vật lý lượng tử và Vật lý hạt
Hơn một trăm năm sau khi nền móng Vật lý lượng tử được Planck, Einstein, Dirac, Schrodinger, Heisenberg, và Feynman, xây dựng lên, thế giới lượng tử vẫn còn quá nhiều điều khó hiểu và khó tiếp cận. Vật lý hạt, ở một thái cực khác , được xây dựng một cách rất hệ thống tiêu biểu phải kể đến Mô hình chuẩn cũng như một lọat khám phá mới từ những hệ thống phòng thí nghiệm đa quốc gia, với vốn đầu tư hàng tỷ đô la. Không phải bàn cãi, đây chính là hai lĩnh vực được đầu tư nhiều tiền bạc và chất xám nhất hiện nay. Thông tin từ các blog sẽ giúp các bạn tiếp cận với những hướng phát triển và làm sáng tỏ những khúc mắc liên quan đến hai trụ cột này.

1. Cohaerence: Here you can track the latest research developments in research in quantum mechanics and information science.
2. Michael Nielson: Michael Nielsen is one of the pioneers of quantum computation, and you can read more about his personal and professional interests on this blog.
3. Life on the Lattice: On this site, Georg von Hippel shares his thoughts on science issues including particle physics and quantum chromodynamics.
4. Quantum Diaries: Make sure to bookmark this site if you’re interested in quantum and particle physics, as it contains posts about the work of numerous physicists around the world.
5. Shtetl-Optimized: The author of this blog is an Assistant Professor of Electrical Engineering and Computer Science at MIT and writes frequently about quantum computing.
6. The Quantum Pontiff: Here you’ll find interesting posts on quantum computing, mathematics and computer science from Professor Dave Bacon.
7. Information Processing: Steve Hsu, Professor of physics at the University of Oregon, shares his thoughts, news items and research interests on quantum field theory here.
8. atdotde: Ever wanted to know more about string theory? Read about that and more on Robert Helling’s blog.
9. Cycle Quark: This blogger spent many years working as a particle physicist but on this site posts about a host of science and technology issues.
10. Particle Physics at Discovery’s Horizon: This site is a great place to learn more about the large Hadron Collider near Geneva, Switzerland and the discoveries being made there.
11. A Quantum Diaries Survivor: If you want to get an expert opinion on the field of particle physics, check out this blog, written by an experimental particle physicist working with the CMS experiment at CERN and the CDF experiment at Fermilab.
12. Resonaances: Visit this blog to read posts on particle theory and the work being done at CERN and other locations around the world.

Vật lý thiên văn
Vật lý thiên văn cũng là một mảng có nhiều nhà nghiên cứu nhất, vũ trụ và bao điều bí ẩn vẫn luôn thu hút sự tò mò và khám phá của con người. Những bài báo được tham khảo nhiều nhất năm vừa qua đều liên quan đến lĩnh vực vật lý thiên văn, điều đó chứng tỏ sự quan tâm của giới khoa học đến lĩnh vực thú vị này.

1. Cosmic Variance: Check out this Discovery News blog to read more about everything space related, from shuttle launches to telescopes.
2. Bad Astronomy: Often cited as one of the best blogs of it’s kind, this site offers loads of information on debunking bad science as well as posting interesting tidbits about space exploration and discoveries.
3. Leaves on the Line: Andrew Jaffe, astrophysicist at Imperial College London, posts on everything from art to science on this blog.
4. Asymptotia: Clifford V. Johnson, a professor at the Department of Physics and Astronomy, at the University of Southern California maintains this blog that posts quite a bit about science, but a little bit about everything else as well.
5. The AstroDyke: This blogger divides her posts between astrophysics, science and queer life, giving a balance between social and professional interests.
6. Tom’s Astronomy Blog: If you simply love everything to do with astronomy and the science of space, then you’ll appreciate the news and views offered on this blog.
7. The e-Astronomer: Written by a Professor of Astronomy at the University of Edinburgh, this blog posts on social and scientific issues as well as providing access to the professor’s own musings as well.
8. Dynamics of Cats: Blogger Steinn Sigurðsson is an astrophysicist at Penn State, and posts lots of snippets related to astronomy.
9. In the Dark: Here you’ll find a blog by Peter Coles, Professor of Theoretical Astrophysics in the School of Physics and Astronomy at Cardiff University, with posts on both his personal and professional life.
10. Cosmic Log: This MSNBC blog is a good source of information on the latest discoveries in the fields of physics, astronomy and more.
11. When in Doubt, Do: Here you’ll find a blog written by cosmologist, talking about physics, his career and more.

Giáo sư và sinh viên
Blog và các bài viết ở đó thường gắn liền với những đặc điểm cá nhân, những ghi nhận riêng tư. Rất nhiều các giáo sư và sinh viên đã mở blog để chia sẻ những hiểu biết của mình, những trải nghiệm liên quan đến quá trình học tập, nghiên cứu và ứng dụng Vật lý.

1. Uncertain Principles: Check out this blog to read more about physics, politics and pop culture and all the places they intersect written by Professor Chad Orzel.
2. Dot Physics: If you’re not a physics expert but want to start learning about the topic, this blog can be a great place to start, with posts on some of the basics of physics, related so even non-experts can understand.
3. Watered Down Physics: Alan Reifman is a professor of Human Development and Family Studies at Texas Tech, but in this blog, he posts on a range of physics and mathematical topics.
4. Ted Bunn’s Blog: Check out this link for a blog by an assistant professor in the physics department of the University of Richmond, with posts on a range of topics but focusing largely on cosmology.
5. Life as a Physicist: This blog is maintained by a particle physicist and professor at the University of Washington in Seattle.
6. Imaginary Potential: This blog is a collection of posts from grad students and post docs at colleges like MIT, Yale, and UCSD.
7. Soul Physics: This blog isn’t written by a physicist but instead Bryan Roberts, a PhD student in History and Philosophy of Science at the University of Pittsburgh, but it contains some great thoughts on the history and deeper issues behind the science.
8. metadatta: Get information gathered by this student on recent research in condensed matter physics, biological physics, or statistical physics as well as other topics.

Các nhà vật lý
Nhiều nhà toán học, vật lý tên tuổi, đã từng nhận giải thưởng Fields hay Nobel đều đã mở blog để làm nơi giao lưu với đồng nghiệp và sinh viên khắp nơi trên thế giới, cùng chia sẻ niềm vui khám phá về bộ môn Vật lý cũng như các bộ môn khoa học cơ bản.

1. Physics and Physicists: Get a take on the world of physics and physicists from a physicist on this blog.
2. the reference frame: Here you can read about Czech physicist Lubos Motl’s take on physics and a number of other political, academic and social topics.
3. Backreaction: Check out this blog to pick the brains of two theoretical physicists.
4. Swans on Tea: On this site you’ll find posts on physics, the latest technology, and more from a physicist at the US Naval Observatory.
5. The n-Category Cafe: This group blog brings together posts from both mathematicians and physicists.
6. Peculiar Velocity: Learn more about the work, interests and musings of Ben Lillie, physicist and writer, on this blog.

Vật lý vui
Vật lý không chỉ là nhưng công thức, những hình vẽ hay những lời giải khô khan, nó là cả nụ cười và niềm vui qua quá trình đọc, tìm hiểu và khám phá những điều kỳ thú, mới mẻ.

1. Cocktail Party Physics: This blog is a great place to find science information, news and commentary with a fun, funky twist.
2. Physics Buzz: Here you’ll find fascinating physics news and a fun take on many physics related topics.
3. Talk Like a Physicist: This blog aims to take an informational and sometimes amusing approach to talking about physics topics.
4. Strange Paths: Take a look at this blog to gain a better understanding of some of the amazing and often beautiful ways that the world works in often invisible ways. While it’s not always easy to understand, there are a lot of pictures to look at if you get lost.

Vật lý và thế giới xung quanh
Còn rất nhiều lĩnh vực và chủ đề liên quan trực tiếp lẫn gián tiếp đến bộ môn Vật lý. Các blog sau đây cũng đóng góp không nhỏ vào bức tranh blog Vật lý năm vừa qua.

1. Physiology physics woven fine: Take a look at this blog to learn more about the field of biophysics.
2. Not Even Wrong: Those hoping to better understand the mathematical side of physics should check out this blog.
3. Nanoscale Views: This blogger wanted to give condensed matter and nanoscale physics some love too, so he started this blog full of information and news items on the subject.
4. incoherently scattered ponderings: This experimental condensed matter physicist shares thoughts on science, social and career-related issues here.

I’ve often been asked the question: how do you become a physicist? Let me first say that physicists, from a fairly early age, are fascinated by the universe and its fantastic wonders. We want to be part of the romantic, exciting adventure to tease apart its mysteries and understand the nature of physical reality.

That’s the driving force behind our lives. We are more interested in black holes and the origin of the universe than with making tons of money and driving flashy cars. We also realize that physics forms the foundation for biology, chemistry, geology, etc. and the wealth of modern civilization. We realize that physicists pioneered the pivotal discoveries of the 20th century which revolutionized the world (e.g. the transistor, the laser, splitting the atom, TV and radio, MRI and PET scans, quantum theory and relativity, unraveling the DNA molecule was done by physicists.

But people often ask the question: do I have to be an Einstein to become a physicist? The answer is NO. Sure, physicists have to be proficient in mathematics, but the main thing is to have that curiosity and drive. One of the greatest physicists of all time, Michael Faraday, started out as a penniless, uneducated apprentice, but he was persistent and creative and then went on to revolutionize modern civilization with electric motors and dynamos. Much of the worlds gross domestic product depends on his work.

Einstein also said that behind every great theory there is a simple physical picture that even lay people can understand. In fact, he said, if a theory does not have a simple underlying picture, then the theory is probably worthless. The important thing is the physical picture; math is nothing but bookkeeping.

Steps to becoming a Physicist:

1) in high school, read popular books on physics and try to make contact with real physicists, if possible. (Role models are extremely important. If you cannot talk to a real physicist, read biographies of the giants of physics, to understand their motivation, their career path, the milestones in their career.) A role model can help you lay out a career path that is realistic and practical. The wheel has already been invented, so take advantage of a role model. Doing a science fair project is another way to plunge into the wonderful world of physics. Unfortunately, well-meaning teachers and counselors, not understanding physics, will probably give you a lot of useless advice, or may try to discourage you. Sometimes you have to ignore their advice.

Don’t get discouraged about the math, because you will have to wait until you learn calculus to understand most physics. (After all, Newton invented calculus in order to solve a physics problem: the orbit of the moon and planets in the solar system.)

Get good grades in all subjects and good SAT scores (i.e. don’t get too narrowly focused on physics) so you can be admitted to a top school, such as Harvard, Princeton, Stanford, MIT, Cal Tech. (Going to a top liberal arts college is sometimes an advantage over going to an engineering school, since it’s easier to switch majors if you have a career change.)

2) next, study four years of college. Students usually have to declare their majors in their sophomore (2nd) year in college; physics majors should begin to think about doing (a) experimental physics or (b) theoretical physics and choosing a specific field.

The standard four year curriculum:

a) first year physics, including mechanics and electricity and magnetism (caution: many universities make this course unnecessarily difficult, to weed out weaker engineers and physicists, so don’t be discouraged if you don’t ace this course! Many future physicists do poorly in this first year course because it is made deliberately difficult.).

Also, take first (or second) year calculus.

b) second year physics – intermediate mechanics and EM theory.

Also, second year calculus, including differential equations and surface and volume integrals.

c) third year physics – a selection from: optics, thermodynamics, statistical mechanics, beginning atomic and nuclear theory

d) four year physics – elementary quantum mechanics

Within physics, there are many sub-disciplines you can choose from. For example, there is solid state, condensed matter, low temperature, and laser physics, which have immediate applications in electronics and optics. My own field embraces elementary particle physics as well as general relativity. Other branches include nuclear physics, astrophysics, geophysics, biophysics, etc.

Often you can apply for industrial jobs right after college. But for the higher paying jobs, it’s good to get a higher degree.

3) so then there is graduate school. If your goal is to teach physics at the high school or junior college level, then obtaining a Masters degree usually involves two years of advanced course work but no original research. There is a shortage of physics teachers at the junior college and high school level.

If you want to become a research physicist or professor, you must get a Ph.D., which usually involves 4 to 5 years (sometimes more), and involves publishing original research. (This is not as daunting as it may seem, since usually this means finding a thesis advisor, who will simply assign you a research problem or include you in their experimental work.) Funding a Ph.D. is also not as hard as it seems, since a professor will usually have a grant or funding from the department to support you at a rate of about $12,000 per year or more. Compared to English or history graduate students, physics graduate students have a very cushy life.

After a Ph.D: Three sources of jobs

a) government

b) industry

c) the university

Government work may involve setting standards at the National Institute for Standards and Technology (the old National Bureau of Standards), which is important for all physics research. Government jobs pay well, but you will never become wealthy being a government physicist. But government work may also involve working in the weapons industry, which I highly discourage. (Not only for ethical reasons, but because that area is being downsized rapidly.)

Industrial work has its ebbs and flows. But lasers and semi-conductor and computer research will be the engines of the 21st century, and there will be jobs in these fields. One rewarding feature of this work is the realization that you are building the scientific architecture that will enrich all our lives. There is no job security at this level, but the pay can be quite good (especially for those in management positions – it’s easier for a scientist to become a business manager than for a business major to learn science.) In fact, some of the wealthiest billionaires in the electronics industry and Silicon Valley came from physics/engineering backgrounds and then switched to management or set up their own corporation.

But I personally think a university position is the best, because then you can work on any problem you want. But jobs at the university are scarce; this may mean taking several two-year “post-doctorate” positions at various colleges before landing a teaching position as an assistant professor without tenure (tenure means you have a permanent position). Then you have 5-7 more years in which to establish a name for yourself as an assistant professor.

If you get tenure, then you have a permanent position and are promoted to associate professor and eventually full professor. The pay may average between $40,000 to $100,000, but there are also severe obstacles to this path.

In the 1960s, because of Sputnik, a tremendous number of university jobs opened up. The number of professors soared exponentially. But this could not last forever. By the mid 1970s, job expansion began inevitably to slow down, forcing many of my friends out of work. So the number of faculty positions leveled off in the 1980s.

Then, many people predicted that, with the retirement of the Sputnik-generation, new jobs at the universities would open up in the 90s. Exactly the opposite took place. First, Congress passed legislation against age-discrimination, so professors could stay on as long as they like. Many physicists in their seventies decided to stay on, making it difficult to find jobs for young people. Second, after the cancellation of the SSC and the end of the Cold War, universities and government began to slowly downsize the funding for physics. As a result, the average age of a physicist increases 8 months per year, meaning that there is very little new hiring.

As I said, physicists do not become scientists for the money, so I don’t want to downplay the financial problems that you may face. In fact, many superstring theorists who could not get faculty jobs went to Wall Street (where they were incorrectly called “rocket scientists”). This may mean leaving the field. However, for the diehards who wish to do physics in spite of a bad job market, you may plan to have a “fall-back” job to pay the bills (e.g. programming) while you conduct research on your own time.

But this dismal situation cannot last. Within ten years, the Sputnik-generation will finally retire, hopefully opening up new jobs for young, talented physicists. The funding for physics may never rival that of the Cold War, but physics will remain an indispensable part of creating the wealth of the 21st century. There are not many of us (about 30,000 or so are members of the American Physical Society) but we form the vanguard of the future. It also helps to join the APS and receive Physics Today magazine, which has an excellent back page which lists the various job openings around the country.

source: mkaku

GRE Math Section

In the GRE Math section, questions can be classified into the following categories :

GRE Math – Arithmetic
Questions involve

• Arithmetic operations
• Powers
• Operations on radical expressions
• Estimation
• Percent
• Absolute value
• Properties of numbers (e.g. divisibility, prime numbers, odd and even integers)
• Factoring

GRE Math – Algebra
Questions involve

• Rules of exponents
• Factoring and simplifying algebraic expressions
• Understanding concepts of relations and functions
• Solving first and second degree equations and inequalities
• Solving simultaneous equations
• Setting up equations to solve word problems
• Applying basic algebra skills to solve problems

GRE Math- Geometry
Questions involve properties of

• Parallel lines
• Circles and their inscribed central angles
• Triangles
• Rectangles
• Other polygons
• Area
• Perimeter
• Volume
• Pythagoras theorem
• Angle measure in degrees
• Simple coordinate geometry (including slopes, intercepts, and inequalities)

GRE Math – Data Analysis
Questions involve

• Elementary probability
• Basic descriptive statistics
• Mean
• Median
• Mode
• Range
• Standard deviation
• Percentiles
• Interpretation of data in graphs and tables
• Line graphs
• Bar graphs
• Circle graphs
• Frequency distributions

• GRE Math – Quantitative Comparisons
• GRE Math – Problem Solving
• GRE Math – Data Interpretation

GRE Math – Quantitative Comparisons :-

Quantitative comparison in GRE Math measures your ability to:

• Determine the relative sizes of two quantities
• Perceive that not enough information is provided to make such a decision

GRE Math – Quantitative comparison Strategies :

• Convert algebraic expressions to a standard form in order to compare them.
• Avoid performing needless calculations, such as trying to decide how much larger or smaller one quantity is than the other.
• Don’t assume that all variables represent positive integers – be aware of negative numbers, fractions, and zero as possible numbers.
• Geometric figures aren’t always drawn to scale, so don’t make assumptions simply based on the appearance of a figure shown.

GRE Math – Quantitative comparison GRE Sample question :

7x² = 21

Column A    Column B

x               2

A. The quantity in Column A is greater
B. The quantity in Column B is greater
C. The two quantities are equal
D. The relationship cannot be determined from the information given

Answer: B

Problem solving questions in GRE Math section test your:

• Knowledge of maths involving percentages, simultaneous equations, polygons, probability, etc.
• Ability to read, understand, and solve problems quickly and accurately

Each of the questions GRE Math problem solving is followed by five answer choices. You have to select the best of the answer options given.
GRE Math – Problem solving Strategies :

• Determine what is given and what is being asked
• Scan options to decide the level of approximation required
• Avoid long computations
• Scan all options before answering a question

GRE Math – Problem solving GRE Sample question :

In the fig shown, if CP=BP and x=120, then y=

A. 30
B. 45
C. 60
D. 75
E. 90

Answer: C

This is the toughest section in GRE Math. Many have poor Math scores because of the high difficulty of Data intreptation GRE questions. Practice with lots of tough DI questions to do get a good GRE Math score. Data interpretation in GRE Math section measures your ability to:

• Read and interpret data
• Perform statistical calculations on the data provided

The data interpretation questions in GRE Math usually appear in sets and are based on data presented in tables or graphs.
GRE Math – Data Interpretation Strategies :

• Look carefully at the data and understand how it’s presented
• Try to make visual comparisons and estimate products and quotients rather than perform computations.
• For graphs, pay attention to the scales as well as read any accompanying notes
• Answer questions only on the basis of data given.

GRE Math – Data Interpretation GRE Sample question :

In which of the following years did the number of graduate student applications increase the most from that of the previous year?

A. 1985
B. 1986
C. 1988
D. 1990
E. 1991

Answer: B

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“Hãy sợ hãi khi người khác đang tham lam và hãy tham lam khi người khác sợ hãi”. – Warren Buffet

Looking beyond the LHC

Earlier this year more than 100 experimentalists, theorists and machine physicists gathered at a CERN Theory Institute to investigate the impact of early LHC data on the field of particle physics, with particular focus on future accelerators and experiments.

Résumé

Du LHC à un futur collisionneur

Plus de cent physiciens – expérimentateurs, théoriciens ou physiciens des accélérateurs – ont participé à un séminaire au CERN pour étudier l’incidence des premières données du LHC sur la préparation des futurs accélérateurs et expériences. Le but était de donner à la communauté de la physique des particules des outils pour fixer des priorités entre les options. Des résultats inédits dans les premières données du LHC ouvriront des perspectives stimulantes, qui devront être explorées par une nouvelle grande machine. Afin de tirer parti au mieux des possibilités, la communauté de la physique des particules devra s’unir et motiver par des arguments solides la construction d’une telle machine. Le séminaire était l’occasion d’en discuter dès à présent, avant qu’on ne dispose des premiers résultats du LHC.

Fig. 1.

The LHC at CERN is about to start the direct exploration of physics at the tera-electron-volt energy scale. Early ground-breaking discoveries may be possible, with profound implications for our understanding of the fundamental forces and constituents of the universe, and for the future of the field of particle physics as a whole. These first results at the LHC will set the agenda for further possible colliders, which will be needed to study physics at the tera-electron-volt scale in closer detail.

Once the first inverse femtobarns of experimental data from the LHC have been analysed, the worldwide particle-physics community will need to converge on a strategy for shaping the field over the years to come. Given that the size and complexity of possible accelerator experiments will require a long construction time, the decision of when and how to go ahead with a future major facility needs to be undertaken in a timely fashion. Several projects for future colliders are currently being developed and soon it may be necessary to set priorities between these options, informed by whatever the LHC reveals at the tera-electron-volt scale

The CERN Theory Institute “From the LHC to a Future Collider” reviewed the physics goals, capabilities and possible results coming from the LHC and studied how these relate to possible future collider programmes. Participants discussed recent physics developments and the near-term capabilities of the Tevatron, the LHC and other experiments, as well as the most effective ways to prepare for providing scientific input to plans for the future direction of the field. To achieve these goals, the programme of the institute centred on a number of questions. What have we learnt from data collected up to this point? What may we expect to know about the emerging new physics during the initial phase of LHC operation? What do we need to know from the LHC to plan future accelerators? What scientific strategies will be needed to advance from the planned LHC running to a future collider facility? To answer the last two questions, the participants looked at what to expect from the LHC with a specific early luminosity, namely 10 fb^–1, for different scenarios for physics at the tera-electron-volt scale and investigated which strategy for future colliders would be appropriate in each of these scenarios. Figure 1 looks further ahead and indicates a possible luminosity profile for the LHC and its sensitivity to new physics scenarios to come.

Present and future

The institute’s efforts were organized into four broad working groups on signatures that might appear in the early LHC data. Their key considerations were the scientific benefits of various upgrades of the LHC compared with the feasibility and timing of other possible future colliders. Hence, the programme also included a series of presentations on present and future projects, one on each possible accelerator followed by a talk on the strong physics points. These included the Tevatron at Fermilab, the (s)LHC, the International Linear Collider (ILC), the LHeC, the Compact Linear Collider (CLIC) concept and a muon collider.

Working Group 1, which was charged with studying scenarios for the production of a Higgs boson, assessed the implications of the detection of a state with properties that are compatible with a Higgs boson, whether Standard Model (SM)-like or not. If nature has chosen an SM-like Higgs, then ATLAS and CMS are well placed to discover it with 10 fb^–1 (assuming √s = 14 TeV, otherwise more luminosity may be needed) and measure its mass. However, measuring other characteristics (such as decay width, spin, CP properties, branching ratios, couplings) with an accuracy better than 20–30% would require another facility.

The ILC would provide e⁺e^– collisions with an energy of √s = 500 GeV (with an upgrade path to √s = 1 TeV). It would allow precise measurements of all of the quantum numbers and many couplings of the Higgs boson, in addition to precise determinations of its mass and width – thereby giving an almost complete profile of the particle. CLIC would allow e⁺e^–collisions at higher energies, with √s = 1–3 TeV, and if the Higgs boson is relatively light it could give access to more of the rare decay modes. CLIC could also measure the Higgs self-couplings over a large range of the Higgs mass and study directly any resonance up to 2.5 TeV in mass in WW scattering.

Working Group 2 considered scenarios in which the first 10 fb^–1of LHC data fail to reveal a state with properties that are compatible with a Higgs boson. It reviewed complementary physics scenarios such as gauge boson self-couplings, longitudinal vector-boson scattering, exotic Higgs scenarios and scenarios with invisible Higgs decays. Two generic scenarios need to be considered in this context: those in which a Higgs exists but is difficult to see and those in which no Higgs exists at all. With higher LHC luminosity – for instance with the sLHC, an upgrade that gives 10 times more luminosity – it should be possible in many scenarios to determine whether or not a Higgs boson exists by improving the sensitivity to the production and decays of Higgs-like particles or vector resonances, for example, or by measuring WW scattering. The ILC would enable precision measurements of even the most difficult-to-see Higgs bosons, as would CLIC. The latter would be also good for producing heavy resonances.

Working Group 3 reviewed missing-energy signatures at the LHC, using supersymmetry as a representative model. The signals studied included events with leptons and jets, with the view of measuring the masses, spins and quantum numbers of any new particles produced. Studies of the LHC capabilities at √s = 14 TeV show that with 1 fb^–1 of LHC luminosity, signals of missing energy with one or more additional leptons would give sensitivity to a large range of supersymmetric mass scales. In all of the missing-energy scenarios studied, early LHC data would provide important input for the technical and theoretical requirements for future linear-collider physics. These include the detector capabilities where, for example, the resolution of mass degeneracies could require exceptionally good energy resolution for jets, running scenarios, required threshold scans and upgrade options – for a γγ collider, for instance, and/or an e⁺e^– collider operating in “GigaZ” mode at the Z mass. The link with dark matter was also explored in this group.

CLIC test facility, CTF3

Working Group 4 studied examples of phenomena that do not involve a missing-energy signature, such as the production of a new Z’ boson, other leptonic resonances, the impact of new physics on observables in the flavour sector, gravity signatures at the tera-electron-volt scale and other exotic signatures of new physics. The sLHC luminosity upgrade has the capability to provide additional crucial information on new physics discovered during early LHC running, as well as to increase the search sensitivity. On the other hand, a future linear collider – with its clean environment, known initial state and polarized beams – is unparalleled in terms of its abilities to conduct ultraprecise measurements of new and SM phenomena, provided that the new-physics scale is within reach of the machine. For example, in the case of a Z’, high-precision measurements at a future linear collider would provide a mass reach that is more than 10 times higher than the centre-of-mass energy of the linear collider itself. Attention was also given to the possibility of injecting a high-energy electron beam onto the LHC proton beam to provide an electron–proton collider, the LHeC (CERN Courier April 2009 p22). Certain phenomena such as the properties of leptoquarks could be studied particularly well with such a collider; for other scenarios, such as new heavy gauge-boson scattering, the LHeC can contribute crucial information on the couplings, which are not accessible with the LHC alone.

The physics capabilities of the sLHC, the ILC and CLIC are relatively well understood but will need refinement in the light of initial LHC running. In cases where the exploration of new physics might be challenging at the early LHC, synergy with a linear collider could be beneficial. In particular, a staged approach to linear-collider energies could prove promising.

The purpose of this CERN Theory Institute was to provide the particle-physics community with some tools for setting priorities among the future options at the appropriate time. Novel results from the early LHC data will open exciting prospects for particle physics, to be continued by a new major facility. In order to seize this opportunity, the particle-physics community will need to unite behind convincing and scientifically solid motivations for such a facility. The institute provided a framework for discussions now, before the actual LHC results start to come in, on how this could be achieved. In this context, the workshop report was also mentioned and made available to the European Strategy Session of the CERN Council meetings in September 2009. We now look forward to the first multi-tera-electron-volt collisions in the LHC, as well as to the harvest of new physics that these results will provide.

• For more about the institute, seehttp://indico.cern.ch/conferenceDisplay.py?confId=40437. The institute summary is available athttp://arxiv.org/abs/0909.3240.

About the author

Albert De Roeck, John Ellis, CERN, and Sven Heinemeyer, ICFA (CSIC Santander), for the organizers of the CERN Theory Institute

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Bài này tôi viết nhân dịp thành tựu của Hòa Thượng Thích Học Toán được báo Time đưa vào 1 trong 10 sự kiện khoa học quan trọng nhất của năm 2009.  Tôi thực ra không biết gì lắm về chương trình Langlands, hay quan hệ của nó với Vật lý, nhưng sự kiện này làm tôi quyết định mạnh dạn viết ra những gì mình biết, ở trình độ khoa học thường thức thôi, coi như một món quà nhỏ gửi tặng Hòa Thượng. Bạn đọc sẽ thấy đoạn cuối hơi bị “cụt”. Đầu đề bài viết đáng lẽ phải khiêm tốn hơn, nhưng thôi cứ để thế để lôi kéo bạn đọc gần xa.

Trước hết, chúng ta nhắc lại một số thức phổ thông về tương tác điện từ.

Chắc ai cũng nhớ định luật Coulomb: hai điện tích  và  tương tác với nhau bằng lực

Nếu  va  cùng dấu thì đây là lực đẩy, còn nếu  và  ngược dấu thì nó là lực hút. Ta sẽ viết công thức này theo một cách khác. Do công (tức là năng lượng) = lực  quãng đường, thế năng giữa hai hạt đó bằng:

Bây giờ giả sử ta giam hai hạt có điện tích  ở trong một cái hộp có kích thước mỗi chiều là .

Theo công thức trên thế năng của hai hạt là khoảng . Động năng thì là bao nhiêu? Theo lý thuyết lượng tử, khi một hạt bị giam vào một cái hộp như vậy, thì nó không thể nào đứng yên. Nguyên lý bất định của Heisenberg cho biết là xung lượng  của hạt này phải lớn hơn , trong đó  là hằng số Planck: .

Một hạt có xung lượng thì phải có năng lượng. Theo quan điểm của thuyết tương đối thì năng lượng và xung lượng được hợp nhất thành một vectơ 4 chiều: , trong đó  là tốc độ ánh sáng.  Không gian này là không gian Minkowski, ở đó độ dài của véctơ đó là  (chú ý dấu trừ!). Một hạt có khối lượng là thì độ dài của véctơ này là :

Giả sử kích thước của hộp  rất nhỏ, khi đó  lớn hơn nhiều , và .

Như vậy nếu ta có hai hạt bị giam vào một hộp kích thước , động năng của chúng ít nhất sẽ là , và thế năng là . Tỷ lệ (thế năng)/(động năng) bằng , không phụ thuộc và kích thước của hộp. Thay thế giá trị của , ,  trong tự nhiên vào, con số này bằng 1/137 (chính xác hơn là 1/137.036)  Thế năng nhỏ hơn động năng khoảng 100 lần. Đây là một hằng số cơ bản của tự nhiên, vì lý do lịch sử, nó được gọi là “hằng số cấu trúc tinh tế”. Hầu như tất cả mọi thứ quanh ta (kể cả hóa học, sinh vật học) đều phụ thuộc vào hằng số này. Ví dụ ta có khoảng 100 nguyên tố hóa học trong bảng tuần hoàn chính là do nghịch đảo của hằng số này bằng khoảng 100.

Tuy thế trong tự nhiên có một điểm rất lạ mà không ai giải thích được: đó là điện tích của tất cả các hạt đều bằng một số nguyên nhân cho điện tích cơ bản. Điện tích cơ bản là 1/3 điện tích electron. Các hạt quark có thể có điện tích 2 lần hay 1 lần điện tích cơ bản nhưng không có hạt nào có điện tích, ví dụ, bằng 1/4 hay  lần điện tích của electron.

Tại sao lại như vậy?

Năm 1931 Paul Dirac đưa ra một lời giải thích hết sức đặc sắc. Ông ta giả thiết thế giới không những chỉ có điện tích, mà có cả “từ tích”. Từ tích, hay còn gọi là đơn cực từ, là nguồn của từ trường. Bình thường một nam châm bao giờ cũng có cực bắc và cực nam.

Ta cứ tưởng tượng có thể tách hai cực của nam châm ra khỏi nhau, thì hai phần đó là hai đơn cực từ. Đơn cực từ chỉ mang một cực, hoặc là bắc, hoặc là nam, cũng như điện tích có thể dương, có thể âm.

Ta sẽ bàn việc đơn cực từ có tồn tại thật trong vũ trụ không sau đây một chút.

Hai đơn cực từ cũng tương tác với nhau giống như định luât Coulomb, nhưng ta thay điện tích bằng từ tích: . Nhưng Dỉrac tìm ra là khi ta lấy một cặp bất kỳ bao gồm một điện tích  và một từ tích , cơ học lượng tử đòi hỏi tích của  và  phải là một số nguyên lần :

Như vậy chỉ cần trong vũ trụ có một từ tích có giá trị bằng , thì tất cả các điện tích phải là bội của . Điều này giải thích tại sao các điện tích phải là bội của một điện tích cơ bản. Ngược lại, nếu  là điện tích nhỏ nhất trong thiên nhiên, thì tất cả các từ tích phải là bội của .

Lời giải thích này của Dỉrac hết sức thông minh, nhưng cho đến nay ta vẫn chưa tìm thấy từ tích nào trong vũ trụ. Cũng có thể chúng rất nặng, nên các máy gia tốc chưa tạo ra được chúng.

Nhưng trên giấy các nhà vật lý lý thuyết có thể “sáng tạo” ra những thế giới mới trong đó có cả điện tích lẫn từ tích. Một trong những thế giới này gọi là “N=4 supersymmetric Yang-Mills theory” (N=4 SYM), một lý thuyết trường có nhiều tính chất lý thú. Một trong những tính chất này được các nhà vật lý gọi là “đối ngẫu”: người ta nghĩ rằng N=4 SYM với điện tích cơ bản  và từ tích cơ bản bằng có thể biến đổi thành N=4 SYM với điện tích cơ bản , từ tích cơ bản , bằng một phép đổi biến.  Đối ngẫu này trong vật lý được gọi là đối ngẫu điện từ, hay đối ngẫu Montonen-Olive, hay đối ngẫu S. Nó là một giả thuyết chưa ai chứng minh được chặt chẽ, mặc dù có nhiều lý do để ta tin nó là đúng.

Theo lời kể của Edward Witten thì năm 2004, sau khi nghe Ben-Zvi, ông ta đã hiểu rằng đối ngẫu Montonen-Olive này có liên quan đến đối ngẫu Langlands hình học.  Sau đó Kapustin và Witten viết một bài báo dài hơn 200 trang giải thích sự liên quan này. Tất cả những điều này tôi chỉ biết rất lờ mờ thôi, nhưng có vẻ chương trình Langlands có liên hệ mật thiết với một số tính chất cơ bản, và còn phần nào bí hiểm, của một số lý thuyết trường. Kapustin và Witten viết: “the geometric Langlands program for complex surfaces… can be understood as a chapter in quantum field theory.”

Xin cáo lỗi các bạn vì trình độ còn kém nên không thể giải thích công trình của Kapustin và Witten chi tiết hơn được. Hy vọng đến một lúc nào đó tôi sẽ hiểu tốt hơn.  Có thể trong tương lai công trình của Hòa Thượng sẽ nằm trong cơ sở của các sách giáo khoa vật lý!

Một lần nữa xin chúc mừng Hòa Thượng Thích Học Toán!

Đàm Thanh Sơn.